1984-07-27 10:28:48 +00:00
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.\" $Header$
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1984-06-29 11:21:50 +00:00
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.ds OF \\fBtest~off:~\\fR
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.ds ON \\fBtest~on:~~\\fR
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.ds AL \\fBtest~all:~\\fR
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.ll 72
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.wh 0 hd
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.wh 60 fo
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.de hd
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'sp 5
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..
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.de fo
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'bp
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..
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.tr ~
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. TITLE
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.de TL
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.sp 15
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.ce
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\\fB\\$1\\fR
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..
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. AUTHOR
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.de AU
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.sp 15
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.ce
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by
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.sp 2
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.ce
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\\$1
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..
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. DATE
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.de DA
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.sp 3
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.ce
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( Dated \\$1 )
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..
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. INSTITUTE
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.de VU
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.sp 3
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.ce 4
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Wiskundig Seminarium
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Vrije Universiteit
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De Boelelaan 1081
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Amsterdam
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..
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. PARAGRAPH
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.de PP
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.sp
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.ti +5
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..
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.nr CH 0 1
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. CHAPTER
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.de CH
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.nr SH 0 1
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.bp
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\\fB\\n+(CH.~\\$1\\fR
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.PP
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..
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. SUBCHAPTER
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.de SH
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.sp 3
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\\fB\\n(CH.\\n+(SH.~\\$1\\fR
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.PP
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..
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. INDENT START
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.de IS
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. INDENT END
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.de IE
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.in -5
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.sp
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. DOUBLE INDENT START
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.de DS
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.de DE
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. EQUATION START
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.de EQ
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.sp
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.nf
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. EQUATION END
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.de EN
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.fi
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.sp
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..
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. ITEM
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.de IT
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\\fBISO~\\$1:\\fR~\\
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..
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. IMPLEMENTATION 1
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.de I1
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.IS
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.ti -3
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1.~\\
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..
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. IMPLEMENTATION 2
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.de I2
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.ti -3
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2.~\\
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..
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.de CS
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.br
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~-~\\
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..
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.br
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.fi
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.TL "Amsterdam Compiler Kit-Pascal reference manual"
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.AU "Johan W. Stevenson"
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.DA "January 4, 1983"
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.VU
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.CH "Introduction"
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This document refers to the (March 1980) ISO standard proposal for Pascal [1].
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Ack-Pascal complies with the requirements of this proposal almost completely.
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The standard requires an accompanying document describing the
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implementation-defined and implementation-dependent features,
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the reaction on errors and the extensions to standard Pascal.
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These four items will be treated in the rest of this document,
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each in a separate chapter.
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The other chapters describe the deviations from the standard and
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the list of options recognized by the compiler.
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.PP
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The Ack-Pascal compiler produces code for an EM machine as defined in [2].
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It is up to the implementor of the EM machine to decide whether errors like
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integer overflow, undefined operand and range bound error are recognized or not.
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For these errors the reaction of some known implementations is given.
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.PP
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There does not (yet) exist a hardware EM machine.
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Therefore, EM programs must be interpreted, or translated into
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instructions for a target machine.
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For the following implementations the behavior is documented:
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.I1
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an interpreter running on a PDP-11.
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Normally the interpreter performs some tests to detect undefined
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integers, integer overflow, range errors, etc.
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However, an option of the interpreter is to skip these tests.
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Another option is to perform some extra tests
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to check for instance the number of actual parameter
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words against the number expected by
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the called procedure.
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We will refer to these modes of operation as 'test all', 'test on' and 'test off'.
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.I2
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a translator into PDP-11 instructions.
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.IE
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.CH "Implementation-defined features"
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For each implementation-defined feature mentioned in the ISO standard
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we give the section number, the quotation from that section and the definition.
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First we quote the definition of implementation-defined:
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.DS
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Those parts of the language which may differ between processors, but which
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will be defined for any particular processor.
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.DE
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.IT 6.1.7
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Each string-character shall denote an implementation-defined value of char-type.
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.IS
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All 7-bits ASCII characters except linefeed LF (10) are allowed.
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Note that an apostrophe ' must be doubled within a string.
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.IE
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.IT 6.4.2.2
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The values of type real shall be an implementation-defined subset
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of the real numbers denoted as specified by 6.1.5.
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.IS
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The format of reals is not defined in EM.
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Even the size of reals depends on the implementation.
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The compiler can be instructed, by the f-option, to use a different
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size for real values.
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The size of reals is preset by the calling program \fIack\fP
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[4] to
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the proper size.
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For each implementation of EM the following constants must be defined:
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epbase: the base for the exponent part
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epprec: the precision of the fraction
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epemin: the minimum exponent
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epemax: the maximum exponent
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.br
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These constants must be chosen so that zero and all numbers with
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exponent e in the range
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.EQ
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epemin <= e <= epemax
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.EN
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and fraction-parts of the form
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.EQ
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f = +_ f\d1\u.b\u-1\d + ... + f\depprec\u.b\u-epprec\d
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.EN
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where
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.EQ
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f\di\u = 0,...,epbase-1 and f\d1\u <> 0
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.EN
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are possible values for reals.
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All other values of type real are considered illegal.
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(See [3] for more information about these constants).
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.br
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For the known EM implementations these constants are:
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.I1
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epbase = 2
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.br
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epprec = 24
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.br
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epemin = -127
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.br
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epemax = +127
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.I2
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ditto
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.IE
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.IT 6.4.2.2
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The type char shall be the enumeration of a set of implementation-defined
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characters, some possibly without graphic representations.
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.IS
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The 7-bits ASCII character set is used, where LF (10) denotes the
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end-of-line marker on text-files.
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.IT 6.4.2.2
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The ordinal numbers of the character values shall be values of integer-type,
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that are implementation-defined, and that are determined by mapping
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the character values on to consecutive non-negative integer values
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starting at zero.
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.IS
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The normal ASCII ordering is used: ord('0')=48, ord('A')=65, ord('a')=97, etc.
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.IE
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.IT 6.4.3.4
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The largest and smallest values of integer-type
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permitted as numbers of a value
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of a set-type shall be implementation-defined.
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.IS
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The smallest value is 0. The largest value is default 15, but can be
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changed by using the i-option of the compiler up to a maximum
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of 32767.
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The compiler allocates as many bits for set-type variables as are necessary
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to store all possible values of the host-type of the base-type of the set,
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rounded up to the nearest multiple of 16.
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If 8 bits are sufficient then only
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8 bits are used if part of a packed structure.
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Thus, the variable s, declared by
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.EQ
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var s: set of '0'..'9';
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.EN
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will contain 128 bits, not 10 or 16.
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These 128 bits are stored in 16 bytes, both for packed and unpacked sets.
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If the host-type of the base-type is integer, then the
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number of bits depends on the i-option.
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The programmer may specify how many bits to allocate for these sets.
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The default is 16, the maximum is 32767.
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The effective number of bits is rounded up to the next multiple of 16, or up
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to 8 if the number of bits is less than or equal to 8.
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Note that the use of set-constructors for sets with more than 256 elements
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is far less efficient than for smaller sets.
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.IT 6.7.2.2
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The predefined constant maxint shall be of integer-type and shall denote
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an implementation-defined value, that satisfies the following conditions:
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.sp 1
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.in +5
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.ti -4
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(a)~All integral values in the closed interval from -maxint to +maxint
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shall be values in the integer-type.
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.ti -4
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(b)~Any monadic operation performed on an integer value in this interval
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shall be correctly performed according to the mathematical rules for
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integer arithmetic.
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.ti -4
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(c)~Any dyadic integer operation on two integer values in this same interval
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shall be correctly performed according to the mathematical rules for
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integer arithmetic, provided that the result is also in this interval.
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.ti -4
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(d)~Any relational operation on two integer values in this same interval
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shall be correctly performed according to the mathematical rules for
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integer arithmetic.
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.in -5
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.IS
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The representation of integers in EM is a \fIn\fP*8-bit word using
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two's complement arithmetic.
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Where \fIn\fP is called wordsize.
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The compiler can only generate code for EM with wordsize 2.
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Thus always:
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.EQ
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maxint = 32767
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.EN
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Because the number -32768 may be used to indicate 'undefined', the
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range of available integers depends on the EM implementation:
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.I1
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\*(ON-32767..+32767.
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.br
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\*(OF-32768..+32767.
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.I2
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-32768..+32767.
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.IE
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.IT 6.9.4.2
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The default TotalWidth values for integer, Boolean and real types
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shall be implementation-defined.
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.IS
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The defaults are:
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integer 6
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Boolean 5
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real 13
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.IT 6.9.4.5.1
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ExpDigits, the number of digits written in an exponent part of a real,
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shall be implementation-defined.
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.IS
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ExpDigits is defined as
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.EQ
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ceil(log10(log10(2 ** epemax)))
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.EN
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For the current implementations this evaluates to 2.
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.IT 6.9.4.5.1
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The character written as part of the representation of
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a real to indicate the beginning of the exponent part shall be
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implementation-defined, either 'E' or 'e'.
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.IS
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The exponent part starts with 'e'.
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.IT 6.9.4.6
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The case of the characters written as representation of the
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Boolean values shall be implementation-defined.
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.IS
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The representations of true and false are 'true' and 'false'.
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.IT 6.9.6
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The effect caused by the standard procedure page
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on a text file shall be implementation-defined.
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.IS
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The ASCII character form feed FF (12) is written.
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.IT 6.10
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The binding of the variables denoted by the program-parameters
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to entities external to the program shall be implementation-defined if
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the variable is of a file-type.
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.IS
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The program parameters must be files and all, except input and output,
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must be declared as such in the program block.
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.PP
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The program parameters input and output, if specified, will correspond
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with the UNIX streams 'standard input' and 'standard output'.
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.PP
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The other program parameters will be mapped to the argument strings
|
|
|
|
|
provided by the caller of this program.
|
|
|
|
|
The argument strings are supposed to be path names of the files to be
|
|
|
|
|
opened or created.
|
|
|
|
|
The order of the program parameters determines the mapping:
|
|
|
|
|
the first parameter is mapped onto the first argument string etc.
|
|
|
|
|
Note that input and output are ignored in this mapping.
|
|
|
|
|
.PP
|
|
|
|
|
The mapping is recalculated each time a program parameter
|
|
|
|
|
is opened for reading or writing by a call to the standard procedures
|
|
|
|
|
reset or rewrite.
|
|
|
|
|
This gives the programmer the opportunity to manipulate the list
|
|
|
|
|
of string arguments using the external procedures argc, argv and argshift
|
|
|
|
|
available in libpc [7].
|
|
|
|
|
.IT 6.10
|
|
|
|
|
The effect of an explicit use of reset or rewrite
|
|
|
|
|
on the standard textfiles input or output shall be implementation-defined.
|
|
|
|
|
.IS
|
|
|
|
|
The procedures reset and rewrite are no-ops
|
|
|
|
|
if applied to input or output.
|
|
|
|
|
.CH "Implementation-dependent features"
|
|
|
|
|
For each implementation-dependent feature mentioned in the ISO standard draft,
|
|
|
|
|
we give the section number, the quotation from that section and the way
|
|
|
|
|
this feature is treated by the Ack-Pascal system.
|
|
|
|
|
First we quote the definition of 'implementation-dependent':
|
|
|
|
|
.DS
|
|
|
|
|
Those parts of the language which may differ between processors,
|
|
|
|
|
and for which there need not be a definition for a particular processor.
|
|
|
|
|
.DE
|
|
|
|
|
.IT 5.1.1
|
|
|
|
|
The method for reporting errors or warnings shall be implementation-dependent.
|
|
|
|
|
.IS
|
|
|
|
|
The error handling is treated in a following chapter.
|
|
|
|
|
.IE
|
|
|
|
|
.IT 6.1.4
|
|
|
|
|
Other implementation-dependent directives may be defined.
|
|
|
|
|
.IS
|
|
|
|
|
Except for the required directive 'forward' the Ack-Pascal compiler recognizes
|
|
|
|
|
only one directive: 'extern'.
|
|
|
|
|
This directive tells the compiler that the procedure block of this
|
|
|
|
|
procedure will not be present in the current program.
|
|
|
|
|
The code for the body of this procedure must be included at a later
|
|
|
|
|
stage of the compilation process.
|
|
|
|
|
.PP
|
|
|
|
|
This feature allows one to build libraries containing often used routines.
|
|
|
|
|
These routines do not have to be included in all the programs using them.
|
|
|
|
|
Maintenance is much simpler if there is only one library module to be
|
|
|
|
|
changed instead of many Pascal programs.
|
|
|
|
|
.PP
|
|
|
|
|
Another advantage is that these library modules may be written in a different
|
|
|
|
|
language, for instance C or the EM assembly language.
|
|
|
|
|
This is useful if you want to use some specific EM instructions not generated
|
|
|
|
|
by the Pascal compiler. Examples are the system call routines and some
|
|
|
|
|
floating point conversion routines.
|
|
|
|
|
Another motive could be the optimization of some time-critical program parts.
|
|
|
|
|
.PP
|
|
|
|
|
The use of external routines, however, is dangerous.
|
|
|
|
|
The compiler normally checks for the correct number and type of parameters
|
|
|
|
|
when a procedure is called and for the result type of functions.
|
|
|
|
|
If an external routine is called these checks are not sufficient,
|
|
|
|
|
because the compiler can not check whether the procedure heading of the
|
|
|
|
|
external routine as given in the Pascal program matches the actual routine
|
|
|
|
|
implementation.
|
|
|
|
|
It should be the loader's task to check this.
|
|
|
|
|
However, the current loaders are not that smart.
|
|
|
|
|
Another solution is to check at run time, at least the number of words
|
|
|
|
|
for parameters. Some EM implementations check this:
|
|
|
|
|
.I1
|
|
|
|
|
\*(ALthe number of words passed as parameters is checked, but this will not catch all faulty cases.
|
|
|
|
|
.br
|
|
|
|
|
\*(ONnot checked.
|
|
|
|
|
.I2
|
|
|
|
|
not checked.
|
|
|
|
|
.IT 6.7.2.1
|
|
|
|
|
The order of evaluation of the operands of a dyadic operator
|
|
|
|
|
shall be implementation-dependent.
|
|
|
|
|
.IS
|
|
|
|
|
Operands are always evaluated, so the program part
|
|
|
|
|
.EQ
|
|
|
|
|
if (p<>nil) and (p^.value<>0) then
|
|
|
|
|
.EN
|
|
|
|
|
is probably incorrect.
|
|
|
|
|
.PP
|
|
|
|
|
The left-hand operand of a dyadic operator is almost always evaluated
|
|
|
|
|
before the right-hand side.
|
|
|
|
|
Some peculiar evaluations exist for the following cases:
|
|
|
|
|
.IS
|
|
|
|
|
.ti -3
|
|
|
|
|
1.~\
|
|
|
|
|
the modulo operation is performed by a library routine to
|
|
|
|
|
check for negative values of the right operand.
|
|
|
|
|
.IE
|
|
|
|
|
.sp
|
|
|
|
|
.ti -3
|
|
|
|
|
2.~\
|
|
|
|
|
the expression
|
|
|
|
|
.EQ
|
|
|
|
|
set1 <= set2
|
|
|
|
|
.EN
|
|
|
|
|
where set1 and set2 are compatible set types is evaluated in the
|
|
|
|
|
following steps:
|
|
|
|
|
.IS
|
|
|
|
|
.CS
|
|
|
|
|
evaluate set2
|
|
|
|
|
.CS
|
|
|
|
|
evaluate set1
|
|
|
|
|
.CS
|
|
|
|
|
compute set2+set1
|
|
|
|
|
.CS
|
|
|
|
|
test set2 and set2+set1 for equality
|
|
|
|
|
.IE
|
|
|
|
|
This is the only case where the right-hand side is computed first.
|
|
|
|
|
.sp
|
|
|
|
|
.ti -3
|
|
|
|
|
3.~\
|
|
|
|
|
the expression
|
|
|
|
|
.EQ
|
|
|
|
|
set1 >= set2
|
|
|
|
|
.EN
|
|
|
|
|
where set1 and set2 are compatible set types is evaluated in the following steps:
|
|
|
|
|
.IS
|
|
|
|
|
.CS
|
|
|
|
|
evaluate set1
|
|
|
|
|
.CS
|
|
|
|
|
evaluate set2
|
|
|
|
|
.CS
|
|
|
|
|
compute set1+set2
|
|
|
|
|
.CS
|
|
|
|
|
test set1 and set1+set2 for equality
|
|
|
|
|
.IE
|
|
|
|
|
.IT 6.7.3
|
|
|
|
|
The order of evaluation, accessing and binding
|
|
|
|
|
of the actual-parameters for functions
|
|
|
|
|
shall be implementation-dependent.
|
|
|
|
|
.IS
|
|
|
|
|
The order of evaluation is from right to left.
|
|
|
|
|
.IT 6.8.2.2
|
|
|
|
|
If access to the variable in an assignment-statement involves the indexing of an array
|
|
|
|
|
and/or a reference to a field within a variant of a record
|
|
|
|
|
and/or the de-referencing of a pointer-variable
|
|
|
|
|
and/or a reference to a buffer-variable,
|
|
|
|
|
the decision whether these actions precede or follow the evaluation
|
|
|
|
|
of the expression shall be implementation-dependent.
|
|
|
|
|
.IS
|
|
|
|
|
The expression is evaluated first.
|
|
|
|
|
.IT 6.8.2.3
|
|
|
|
|
The order of evaluation and binding of the actual-parameters for procedures
|
|
|
|
|
shall be implementation-dependent.
|
|
|
|
|
.IS
|
|
|
|
|
The same as for functions.
|
|
|
|
|
.IT 6.9.6
|
|
|
|
|
The effect of inspecting a text file to which the page
|
|
|
|
|
procedure was applied during generation is
|
|
|
|
|
implementation-dependent.
|
|
|
|
|
.IS
|
|
|
|
|
The formfeed character written by page is
|
|
|
|
|
treated like a normal character, with ordinal value 12.
|
|
|
|
|
.IT 6.10
|
|
|
|
|
The binding of the variables denoted by the program-parameters
|
|
|
|
|
to entities external to the program shall be implementation-dependent unless
|
|
|
|
|
the variable is of a file-type.
|
|
|
|
|
.IS
|
|
|
|
|
Only variables of a file-type are allowed as program parameters.
|
|
|
|
|
.IE
|
|
|
|
|
.CH "Error handling"
|
|
|
|
|
There are three classes of errors to be distinguished.
|
|
|
|
|
In the first class are the error messages generated by the compiler.
|
|
|
|
|
The second class consists of the occasional errors generated by the other
|
|
|
|
|
programs involved in the compilation process.
|
|
|
|
|
Errors of the third class are the errors as defined in the standard by:
|
|
|
|
|
.DS
|
|
|
|
|
An error is a violation by a program of the requirements of this standard
|
|
|
|
|
such that detection normally requires execution of the program.
|
|
|
|
|
.DE
|
|
|
|
|
.SH "Compiler errors"
|
|
|
|
|
The error messages (and the listing) are not generated by the compiler itself.
|
|
|
|
|
The compiler only detects errors and writes the errors in condensed form on
|
|
|
|
|
an intermediate file.
|
|
|
|
|
Each error in condensed form contains:
|
|
|
|
|
.IS
|
|
|
|
|
.CS
|
|
|
|
|
an optional error message parameter (identifier or number).
|
|
|
|
|
.CS
|
|
|
|
|
an error number
|
|
|
|
|
.CS
|
|
|
|
|
a line number
|
|
|
|
|
.CS
|
|
|
|
|
a column number.
|
|
|
|
|
.IE
|
|
|
|
|
Every time the compiler detects an error that does not have influence
|
|
|
|
|
on the code produced by the compiler or on the syntax decisions, a warning
|
|
|
|
|
messages is given.
|
|
|
|
|
If only warnings are generated, compilation proceeds and probably results
|
|
|
|
|
in a correctly compiled program.
|
|
|
|
|
.PP
|
|
|
|
|
The intermediate error file is read by the interface program
|
|
|
|
|
\fIack\fP [4],
|
|
|
|
|
that produces the error messages.
|
|
|
|
|
It uses an other file, the error message file,
|
|
|
|
|
to find an error script line.
|
|
|
|
|
Whenever this error script line contains the character '%', the error messages
|
|
|
|
|
parameter is substituted.
|
|
|
|
|
For negative error numbers the message constructed is prepended with 'Warning: '.
|
|
|
|
|
.PP
|
|
|
|
|
Sometimes the compiler produces several errors for the same file position
|
|
|
|
|
(line number, column number).
|
|
|
|
|
Only the first of these messages is given, because the others are probably
|
|
|
|
|
directly caused by the first one.
|
|
|
|
|
If the first one is a warning while one of its successors for that position
|
|
|
|
|
is a fatal message, then the warning is promoted to a fatal one.
|
|
|
|
|
However, parameterized messages are always given.
|
|
|
|
|
.PP
|
|
|
|
|
The error messages and listing come in three flavors, selected by flags
|
|
|
|
|
given to \fIack\fP [4]:
|
|
|
|
|
.in +10
|
|
|
|
|
.sp
|
|
|
|
|
.ti -8
|
|
|
|
|
default:no listing, one line per error giving the file name
|
|
|
|
|
of the Pascal source file, the line number and the error messages.
|
|
|
|
|
.sp
|
|
|
|
|
.ti -8
|
|
|
|
|
-e:~~~~~for each erroneous line a listing of the line and its predecessor.
|
|
|
|
|
The next line contains one or more characters '^' pointing to the
|
|
|
|
|
places where an error is detected.
|
|
|
|
|
For each error on that line a message follows.
|
|
|
|
|
.sp
|
|
|
|
|
.ti -8
|
|
|
|
|
-E:~~~~~same as for '-e', except that all source lines are listed,
|
|
|
|
|
even if the program is perfect.
|
|
|
|
|
.IE
|
|
|
|
|
.IE
|
|
|
|
|
.SH "Other errors detected at compilation time"
|
|
|
|
|
Two main categories: file system problems and table overflow.
|
|
|
|
|
Problems with the file system may be caused by protection (you may not read
|
|
|
|
|
or create files) or by space problems (no space left on device; out of inodes;
|
|
|
|
|
too many processes).
|
|
|
|
|
Table overflow problems are often caused by peculiar source programs:
|
|
|
|
|
very long procedures or functions, a lot of strings.
|
|
|
|
|
Table overflow problems can sometimes be cured
|
|
|
|
|
by giving a flag (-sl when producing e.out files) to \fIack\fP [4].
|
|
|
|
|
.PP
|
|
|
|
|
Extensive treatment of these errors is outside the scope of this manual.
|
|
|
|
|
.SH "Runtime errors"
|
|
|
|
|
Errors detected at run time cause an error message to be generated on the
|
|
|
|
|
diagnostic output stream (UNIX file descriptor 2).
|
|
|
|
|
The message consists of the name of the program followed by a message
|
|
|
|
|
describing the error, possibly followed by the source line number.
|
|
|
|
|
Unless the l-option is turned off, the compiler generates code to keep track
|
|
|
|
|
of which source line causes which EM instructions to be generated.
|
|
|
|
|
It depends on the EM implementation whether these LIN instructions
|
|
|
|
|
are skipped or executed:
|
|
|
|
|
.I1
|
|
|
|
|
LIN instructions are always executed. The old line number is saved and
|
|
|
|
|
restored whenever a procedure or function is called.
|
|
|
|
|
All error messages contain this line number, except when the l-option
|
|
|
|
|
was turned off.
|
|
|
|
|
.I2
|
|
|
|
|
same as above, but line numbers are not saved when procedures and functions
|
|
|
|
|
are called.
|
|
|
|
|
.IE
|
|
|
|
|
For each error mentioned in the standard we give the section number,
|
|
|
|
|
the quotation from that section and the way it is processed by the
|
|
|
|
|
Pascal-compiler or runtime system.
|
|
|
|
|
.PP
|
|
|
|
|
For detected errors the corresponding message
|
|
|
|
|
and trap number are given.
|
|
|
|
|
Trap numbers are useful for exception-handling routines.
|
|
|
|
|
Normally, each error causes the program to terminate.
|
|
|
|
|
By using exception-handling routines one can
|
|
|
|
|
ignore errors or perform alternate actions.
|
|
|
|
|
Only some of the errors can be ignored
|
|
|
|
|
by restarting the failing instruction.
|
|
|
|
|
These errors are marked as non-fatal,
|
|
|
|
|
all others as fatal.
|
|
|
|
|
A list of errors with trap number between 0 and 63
|
|
|
|
|
(EM errors) can be found in [2].
|
|
|
|
|
Errors with trap number between 64 and 127 (Pascal errors) are listed in [8].
|
|
|
|
|
.IT 6.4.3.3
|
|
|
|
|
It shall be an error if any field-identifier defined within a variant
|
|
|
|
|
is used in a field-designator unless the value of the tag-field
|
|
|
|
|
is associated with that variant.
|
|
|
|
|
.IS
|
|
|
|
|
This error is not detected.
|
|
|
|
|
Sometimes this feature is used to achieve easy type conversion.
|
|
|
|
|
However, using record variants this way is dangerous, error prone and not portable.
|
|
|
|
|
.IT 6.4.6
|
|
|
|
|
It shall be an error if a value of type T2 must be
|
|
|
|
|
assignment-compatible with type T1, while
|
|
|
|
|
T1 and T2 are compatible ordinal-types and the value of
|
|
|
|
|
type T2 is not in the closed interval specified by T1.
|
|
|
|
|
.IS
|
|
|
|
|
The compiler distinguishes between array-index expressions and the other
|
|
|
|
|
places where assignment-compatibility is required.
|
|
|
|
|
.PP
|
|
|
|
|
Array subscripting is done using the EM array instructions.
|
|
|
|
|
These instructions have three arguments: the array base address,
|
|
|
|
|
the index and the address of the array descriptor.
|
|
|
|
|
An array descriptor describes one dimension by three values:
|
|
|
|
|
the element size, the lower bound on the index and the number of elements
|
|
|
|
|
minus one.
|
|
|
|
|
It depends on the EM implementation whether these bounds are checked:
|
|
|
|
|
.I1
|
|
|
|
|
\*(ONchecked (array bound error, trap 0, non-fatal).
|
|
|
|
|
.br
|
|
|
|
|
\*(OFnot checked
|
|
|
|
|
.I2
|
|
|
|
|
not checked.
|
|
|
|
|
.IE
|
|
|
|
|
The other places where assignment-compatibility is required are:
|
|
|
|
|
.IS
|
|
|
|
|
.CS
|
|
|
|
|
assignment
|
|
|
|
|
.CS
|
|
|
|
|
value parameters
|
|
|
|
|
.CS
|
|
|
|
|
procedures read and readln
|
|
|
|
|
.CS
|
|
|
|
|
the final value of the for-statement
|
|
|
|
|
.IE
|
|
|
|
|
For these places the compiler generates an EM range check instruction, except
|
|
|
|
|
when the r-option is turned off, or when the range of values of T2
|
|
|
|
|
is enclosed in the range of T1.
|
|
|
|
|
If the expression consists of a single variable and if that variable
|
|
|
|
|
is of a subrange type,
|
|
|
|
|
then the subrange type itself is taken as T2, not its host-type.
|
|
|
|
|
Therefore, a range instruction is only generated if T1 is a subrange type
|
|
|
|
|
and if the expression is a constant, an expression with two or more
|
|
|
|
|
operands, or a single variable with a type not enclosed in T1.
|
|
|
|
|
If a constant is assigned, then the EM optimizer removes the range check
|
|
|
|
|
instruction, except when the value is out of bounds.
|
|
|
|
|
.PP
|
|
|
|
|
It depends on the EM implementation whether the range check instruction
|
|
|
|
|
is executed or skipped:
|
|
|
|
|
.I1
|
|
|
|
|
\*(ONchecked (range bound error, trap 1, non-fatal).
|
|
|
|
|
.br
|
|
|
|
|
\*(OFskipped
|
|
|
|
|
.I2
|
|
|
|
|
skipped
|
|
|
|
|
.IE
|
|
|
|
|
.IT 6.4.6
|
|
|
|
|
It shall be an error if a value of type T2 must be
|
|
|
|
|
assignment-compatible with type T1, while T1 and T2 are compatible
|
|
|
|
|
set-types and any member of the value of type T2
|
|
|
|
|
is not in the closed interval specified by the base-type
|
|
|
|
|
of the type T1.
|
|
|
|
|
.IS
|
|
|
|
|
This error is not detected.
|
|
|
|
|
.IT 6.5.4
|
|
|
|
|
It shall be an error if
|
|
|
|
|
the pointer-variable has a nil-value or is undefined at the time
|
|
|
|
|
it is de-referenced.
|
|
|
|
|
.IS
|
|
|
|
|
The EM definition does not specify the binary representation of pointer
|
|
|
|
|
values, so that it is not possible to choose an otherwise illegal
|
|
|
|
|
binary representation for the pointer value NIL.
|
|
|
|
|
Rather arbitrary the compiler uses the integer value zero to represent NIL.
|
|
|
|
|
For all current implementations this does not cause problems.
|
|
|
|
|
.PP
|
|
|
|
|
The size of pointers depends on the implementation and is
|
|
|
|
|
preset in the compiler by \fIack\fP [4].
|
|
|
|
|
The compiler can be instructed, by the p-option, to use
|
|
|
|
|
any size for pointer objects.
|
|
|
|
|
NIL is represented here by the appropriate number of zero words.
|
|
|
|
|
.PP
|
|
|
|
|
It depends on the EM implementation whether de-referencing of a pointer
|
|
|
|
|
with value NIL causes an error:
|
|
|
|
|
.I1
|
|
|
|
|
\*(ONfor every de-reference the pointer value is checked to be legal.
|
|
|
|
|
The value NIL is always illegal.
|
|
|
|
|
Objects addressed by a NIL pointer always cause an error, except
|
|
|
|
|
when they are part of some extraordinary sized structure
|
|
|
|
|
(bad pointer, trap 22, fatal).
|
|
|
|
|
.br
|
|
|
|
|
\*(OFde-referencing for fetching will not cause
|
|
|
|
|
an error to occur.
|
|
|
|
|
However, if the pointer value is used for a store operation,
|
|
|
|
|
a segmentation violation probably results (memory fault, trap 21, fatal).
|
|
|
|
|
(Note: this is only true if the interpreter is executed with coinciding
|
|
|
|
|
address spaces and protected text part. The interpreter must therefore
|
|
|
|
|
be loaded with the '-n' option of the UNIX loader [5]).
|
|
|
|
|
.I2
|
|
|
|
|
de-referencing for a fetch operation will not cause an error.
|
|
|
|
|
A store operation probably causes an error if the '-n' flag is
|
|
|
|
|
specified to \fIack\fP [4] or ld [5] while loading your program.
|
|
|
|
|
.IE
|
|
|
|
|
Some implementations of EM initialize all memory cells for newly
|
|
|
|
|
created variables with a constant that probably causes an error if that variable
|
|
|
|
|
is not initialized with a value of its own type before use.
|
|
|
|
|
For each implementation we give whether memory cells are initialized,
|
|
|
|
|
with what value, and whether this value causes an error if de-referenced.
|
|
|
|
|
.I1
|
|
|
|
|
each memory word is initialized with the bit representation 1000000000000000,
|
|
|
|
|
representing -32768 in 2's complement notation.
|
|
|
|
|
For most small and medium sized programs this value will cause a segmentation
|
|
|
|
|
violation (memory fault, trap 21, fatal).
|
|
|
|
|
.I2
|
|
|
|
|
no initialization.
|
|
|
|
|
Whenever a pointer is de-referenced, without being properly initialized,
|
|
|
|
|
a segmentation violation (memory fault, trap 21, fatal)
|
|
|
|
|
or 'bus error' are possible.
|
|
|
|
|
.IE
|
|
|
|
|
.IT 6.5.5
|
|
|
|
|
It shall be an error if the value of a file-variable f is altered
|
|
|
|
|
while the buffer-variable is an actual variable parameter, or
|
|
|
|
|
an element of the record-variable-list of a with-statement, or both.
|
|
|
|
|
.IS
|
|
|
|
|
This error is not detected
|
|
|
|
|
.IT 6.5.5
|
|
|
|
|
It shall be an error if the value of a file-variable f is altered
|
|
|
|
|
by an assignment-statement which contains the buffer-variable f^ in
|
|
|
|
|
its left-hand side.
|
|
|
|
|
.IS
|
|
|
|
|
This error is not detected.
|
|
|
|
|
.IT 6.6.5.2
|
|
|
|
|
It shall be an error if
|
|
|
|
|
the stated pre-assertion does not hold immediately
|
|
|
|
|
prior to any use of the file handling procedures
|
|
|
|
|
rewrite, put, reset and get.
|
|
|
|
|
.IS
|
|
|
|
|
For each of these four operations the pre-assertions
|
|
|
|
|
can be reformulated as:
|
|
|
|
|
.sp
|
|
|
|
|
rewrite(f):~no pre-assertion.
|
|
|
|
|
.br
|
|
|
|
|
put(f):~~~~~f is opened for writing and f^ is not undefined.
|
|
|
|
|
.br
|
|
|
|
|
reset(f):~~~f exists.
|
|
|
|
|
.br
|
|
|
|
|
get(f):~~~~~f is opened for reading and eof(f) is false.
|
|
|
|
|
.sp
|
|
|
|
|
The following errors are detected for these operations:
|
|
|
|
|
.sp
|
|
|
|
|
rewrite(f):
|
|
|
|
|
.in +10
|
|
|
|
|
.ti -5
|
|
|
|
|
more args expected, trap 64, fatal:
|
|
|
|
|
.br
|
|
|
|
|
f is a program-parameter and the corresponding
|
|
|
|
|
file name is not supplied by the caller of the program.
|
|
|
|
|
.ti -5
|
|
|
|
|
rewrite error, trap 101, fatal:
|
|
|
|
|
.br
|
|
|
|
|
the caller of the program lacks the necessary
|
|
|
|
|
access rights to create the file in the file system
|
|
|
|
|
or operating system problems like table overflow
|
|
|
|
|
prevent creation of the file.
|
|
|
|
|
.in -10
|
|
|
|
|
.sp
|
|
|
|
|
put(f):
|
|
|
|
|
.in +10
|
|
|
|
|
.ti -5
|
|
|
|
|
file not yet open, trap 72, fatal:
|
|
|
|
|
.br
|
|
|
|
|
reset or rewrite are never applied to the file.
|
|
|
|
|
The checks performed by the run time system are not foolproof.
|
|
|
|
|
.ti -5
|
|
|
|
|
not writable, trap 96, fatal:
|
|
|
|
|
.br
|
|
|
|
|
f is opened for reading.
|
|
|
|
|
.ti -5
|
|
|
|
|
write error, trap 104, fatal:
|
|
|
|
|
.br
|
|
|
|
|
probably caused by file system problems.
|
|
|
|
|
For instance, the file storage is exhausted.
|
|
|
|
|
Because IO is buffered to improve performance,
|
|
|
|
|
it might happen that this error occurs if the
|
|
|
|
|
file is closed.
|
|
|
|
|
Files are closed whenever they are rewritten or reset, or on
|
|
|
|
|
program termination.
|
|
|
|
|
.in -10
|
|
|
|
|
.sp
|
|
|
|
|
reset(f):
|
|
|
|
|
.in +10
|
|
|
|
|
.ti -5
|
|
|
|
|
more args expected, trap 64, fatal:
|
|
|
|
|
.br
|
|
|
|
|
same as for rewrite(f).
|
|
|
|
|
.ti -5
|
|
|
|
|
reset error, trap 100, fatal:
|
|
|
|
|
.br
|
|
|
|
|
f does not exist, or the caller has insufficient access rights, or
|
|
|
|
|
operating system tables are exhausted.
|
|
|
|
|
.in -10
|
|
|
|
|
.sp
|
|
|
|
|
get(f):
|
|
|
|
|
.in +10
|
|
|
|
|
.ti -5
|
|
|
|
|
file not yet open, trap 72, fatal:
|
|
|
|
|
.br
|
|
|
|
|
as for put(f).
|
|
|
|
|
.ti -5
|
|
|
|
|
not readable, trap 97, fatal:
|
|
|
|
|
.br
|
|
|
|
|
f is opened for writing.
|
|
|
|
|
.ti -5
|
|
|
|
|
end of file, trap 98, fatal:
|
|
|
|
|
.br
|
|
|
|
|
eof(f) is true just before the call to get(f).
|
|
|
|
|
.ti -5
|
|
|
|
|
read error, trap 103, fatal:
|
|
|
|
|
.br
|
|
|
|
|
unlikely to happen. Probably caused by hardware problems
|
|
|
|
|
or by errors elsewhere in your program that destroyed
|
|
|
|
|
the file information maintained by the run time system.
|
|
|
|
|
.ti -5
|
|
|
|
|
truncated, trap 99, fatal:
|
|
|
|
|
.br
|
|
|
|
|
the file is not properly formed by an integer
|
|
|
|
|
number of file elements.
|
|
|
|
|
For instance, the size of a file of integer is odd.
|
|
|
|
|
.ti -5
|
|
|
|
|
non-ASCII char read, trap 106, non-fatal:
|
|
|
|
|
.br
|
|
|
|
|
the character value of the next character-type
|
|
|
|
|
file element is out of range (0..127).
|
|
|
|
|
Only for text files.
|
|
|
|
|
.in -10
|
|
|
|
|
.IT 6.6.5.3
|
|
|
|
|
It shall be an error to change any variant-part of a variable
|
|
|
|
|
allocated by the form new(p,c1,...,cn) from the variant specified.
|
|
|
|
|
.IS
|
|
|
|
|
This error is not detected.
|
|
|
|
|
.IT 6.6.5.3
|
|
|
|
|
It shall be an error if a variable to be disposed had been allocated
|
|
|
|
|
using the form new(p,c1,...,cn) with more variants specified than
|
|
|
|
|
specified to dispose.
|
|
|
|
|
.IS
|
|
|
|
|
This error can cause more memory to be freed then was allocated.
|
|
|
|
|
Dispose causes a fatal trap 73 when memory already on the free
|
|
|
|
|
list is freed again.
|
|
|
|
|
.IT 6.6.5.3
|
|
|
|
|
It shall be an error if the variants of a variable to be disposed
|
|
|
|
|
are different from those specified by the case-constants to dispose.
|
|
|
|
|
.IS
|
|
|
|
|
This error is not detected.
|
|
|
|
|
.IT 6.6.5.3
|
|
|
|
|
It shall be an error if the value of the pointer parameter of dispose has
|
|
|
|
|
nil-value or is undefined.
|
|
|
|
|
.IS
|
|
|
|
|
The same comments apply as for de-referencing NIL or undefined pointers.
|
|
|
|
|
.IT 6.6.5.3
|
|
|
|
|
It shall be an error if a variable that is identified by the pointer parameter
|
|
|
|
|
of dispose (or a component thereof) is currently either an actual
|
|
|
|
|
variable parameter, or an element of the record-variable-list of a
|
|
|
|
|
with-statement, or both.
|
|
|
|
|
.IS
|
|
|
|
|
This error is not detected.
|
|
|
|
|
.IT 6.6.5.3
|
|
|
|
|
It shall be an error if a referenced-variable created using the second form
|
|
|
|
|
of new is used in its entirety
|
|
|
|
|
as an operand in an expression, or as the variable in an assignment-statement
|
|
|
|
|
or as an actual-parameter.
|
|
|
|
|
.IS
|
|
|
|
|
This error is not detected.
|
|
|
|
|
.IT 6.6.6.2
|
|
|
|
|
It shall be an error if the mathematical defined result of an
|
|
|
|
|
arithmetic function would fall outside the set of values
|
|
|
|
|
of the indicated result.
|
|
|
|
|
.IS
|
|
|
|
|
Except for the errors for undefined arguments,
|
|
|
|
|
the following errors may occur for the arithmetic functions:
|
|
|
|
|
.in +16
|
|
|
|
|
.ti -11
|
|
|
|
|
abs(x):~~~~none.
|
|
|
|
|
.ti -11
|
|
|
|
|
sqr(x):~~~~real underflow, trap 5, non-fatal;
|
|
|
|
|
.br
|
|
|
|
|
real overflow, trap 4, non-fatal
|
|
|
|
|
.ti -11
|
|
|
|
|
sin(x):~~~~real underflow, trap 5, non-fatal
|
|
|
|
|
.ti -11
|
|
|
|
|
cos(x):~~~~real underflow, trap 5, non-fatal
|
|
|
|
|
.ti -11
|
|
|
|
|
exp(x):~~~~error in exp, trap 65, non-fatal (if x>10000);
|
|
|
|
|
.br
|
|
|
|
|
real underflow, trap 5, non-fatal;
|
|
|
|
|
.br
|
|
|
|
|
real overflow, trap 4, non-fatal
|
|
|
|
|
.ti -11
|
|
|
|
|
ln(x):~~~~~error in ln, trap 66, non-fatal ( if x<=0)
|
|
|
|
|
.ti -11
|
|
|
|
|
sqrt(x):~~~error in sqrt, trap 67, non-fatal (if x<0)
|
|
|
|
|
.ti -11
|
|
|
|
|
arctan(x):~real underflow, trap 5, non-fatal;
|
|
|
|
|
.br
|
|
|
|
|
real overflow, trap 4, non-fatal
|
|
|
|
|
.in -16
|
|
|
|
|
.IE
|
|
|
|
|
.IT 6.6.6.2
|
|
|
|
|
It shall be an error if x in ln(x) is not greater than zero.
|
|
|
|
|
.IS
|
|
|
|
|
See above.
|
|
|
|
|
.IT 6.6.6.2
|
|
|
|
|
It shall be an error if x in sqrt(x) is negative.
|
|
|
|
|
.IS
|
|
|
|
|
See above.
|
|
|
|
|
.IT 6.6.6.2
|
|
|
|
|
It shall be an error if
|
|
|
|
|
the integer value of trunc(x) does not exist.
|
|
|
|
|
.IS
|
|
|
|
|
This error is detected (conversion error, trap 10, non-fatal).
|
|
|
|
|
.IT 6.6.6.2
|
|
|
|
|
It shall be an error if
|
|
|
|
|
the integer value of round(x) does not exist.
|
|
|
|
|
.IS
|
|
|
|
|
This error is detected (conversion error, trap 10, non-fatal).
|
|
|
|
|
.IT 6.6.6.2
|
|
|
|
|
It shall be an error if
|
|
|
|
|
the integer value of ord(x) does not exist.
|
|
|
|
|
.IS
|
|
|
|
|
This error can not occur, because the compiler will not allow
|
|
|
|
|
such ordinal types.
|
|
|
|
|
.IT 6.6.6.2
|
|
|
|
|
It shall be an error if
|
|
|
|
|
the character value of chr(x) does not exist.
|
|
|
|
|
.IS
|
|
|
|
|
Except when the r-option is turned off, the compiler generates an EM
|
|
|
|
|
range check instruction. The effect of this instruction depends on the
|
|
|
|
|
EM implementation as described before.
|
|
|
|
|
.IT 6.6.6.2
|
|
|
|
|
It shall be an error if the value of succ(x) does not exist.
|
|
|
|
|
.IS
|
|
|
|
|
Same comments as for chr(x).
|
|
|
|
|
.IT 6.6.6.2
|
|
|
|
|
It shall be an error if the value of pred(x) does not exist.
|
|
|
|
|
.IS
|
|
|
|
|
Same comments as for chr(x).
|
|
|
|
|
.IT 6.6.6.5
|
|
|
|
|
It shall be an error if
|
|
|
|
|
f in eof(f) is undefined.
|
|
|
|
|
.IS
|
|
|
|
|
This error is detected (file not yet open, trap 72, fatal).
|
|
|
|
|
.IT 6.6.6.5
|
|
|
|
|
It shall be an error if
|
|
|
|
|
f in eoln(f) is undefined, or if eof(f) is true at that time.
|
|
|
|
|
.IS
|
|
|
|
|
The following errors may occur:
|
|
|
|
|
.IS
|
|
|
|
|
file not yet open, trap 72, fatal;
|
|
|
|
|
.br
|
|
|
|
|
not readable, trap 97, fatal;
|
|
|
|
|
.br
|
|
|
|
|
end of file, trap 98, fatal.
|
|
|
|
|
.IE
|
|
|
|
|
.IT 6.7.1
|
|
|
|
|
It shall be an error if any variable or function used as an operand in an expression is
|
|
|
|
|
undefined at the time of its use.
|
|
|
|
|
.IS
|
|
|
|
|
Detection of undefined operands is only possible if there is at least one bit
|
|
|
|
|
representation that is not allowed as legal value.
|
|
|
|
|
The set of legal values depends on the type of the operand.
|
|
|
|
|
To detect undefined operands, all newly created variables must be assigned
|
|
|
|
|
a value illegal for the type of the created variable.
|
|
|
|
|
The compiler itself does not generate code to initialize newly created variables.
|
|
|
|
|
Instead, the compiler generates code to allocate some new memory cells.
|
|
|
|
|
It is up to the EM implementation to initialize these memory cells.
|
|
|
|
|
However, the EM machine does not know the types of the variables for which
|
|
|
|
|
memory cells are allocated.
|
|
|
|
|
Therefore, the best an EM implementation can do is to initialize with a value
|
|
|
|
|
that is illegal for the most common types of operands.
|
|
|
|
|
.PP
|
|
|
|
|
For all current EM implementations we will describe whether memory cells
|
|
|
|
|
are initialized, which value is used to initialize, for each operand type
|
|
|
|
|
whether that value is illegal, and for all operations on all operand
|
|
|
|
|
types whether that value is detected as undefined.
|
|
|
|
|
.I1
|
|
|
|
|
\*(ONnew memory words are initialized with -32768.
|
|
|
|
|
Assignment of this value is always allowed. Errors may occur
|
|
|
|
|
whenever undefined operands are used in operations.
|
|
|
|
|
.br
|
|
|
|
|
.ul
|
|
|
|
|
integer:
|
|
|
|
|
-32768 is illegal. All arithmetic operations (except unary +) cause
|
|
|
|
|
an error (undefined integer, trap 8, non-fatal).
|
|
|
|
|
Relational operations do not, except for IN when the left operand is undefined.
|
|
|
|
|
Printing of -32768 using write is allowed.
|
|
|
|
|
.br
|
|
|
|
|
.ul
|
|
|
|
|
real:
|
|
|
|
|
the bit representation of a real, caused by initializing the constituent
|
|
|
|
|
memory words with -32768, is illegal.
|
|
|
|
|
All arithmetic and relational operations (except unary +) cause an error
|
|
|
|
|
(real undefined, trap 9, non-fatal).
|
|
|
|
|
Printing causes the same error.
|
|
|
|
|
.br
|
|
|
|
|
.ul
|
|
|
|
|
char:
|
|
|
|
|
the value -32768 is illegal. For objects of type 'packed array[] of char'
|
|
|
|
|
half the characters will have the value chr(0), which is legal, and the
|
|
|
|
|
others will have the value chr(128), outside the valid ASCII range.
|
|
|
|
|
The relational operators, however, do not cause an error.
|
|
|
|
|
.br
|
|
|
|
|
.ul
|
|
|
|
|
Boolean:
|
|
|
|
|
the value -32768 is illegal. For objects of type 'packed array[] of boolean'
|
|
|
|
|
half the booleans will have the value false, while the others have the value v,
|
|
|
|
|
where ord(v) = 128, naturally illegal.
|
|
|
|
|
However, the Boolean and relational operations do not cause an error.
|
|
|
|
|
.br
|
|
|
|
|
.ul
|
|
|
|
|
set:
|
|
|
|
|
undefined operands of type set can not be distinguished from
|
|
|
|
|
properly initialized ones.
|
|
|
|
|
The set and relational operations, therefore, can never cause an error.
|
|
|
|
|
However, if one forgets to initialize a set of character, then spurious
|
|
|
|
|
characters like '/', '?', 'O', '_' and 'o' appear.
|
|
|
|
|
.sp
|
|
|
|
|
\*(OFnew memory cells are initialized with -32768.
|
|
|
|
|
The only cases where this value causes an error are when
|
|
|
|
|
an undefined operand of type real is used in an arithmetic or relational
|
|
|
|
|
operation (except unary +) or when an undefined real is used as an
|
|
|
|
|
argument to a standard function.
|
|
|
|
|
.I2
|
|
|
|
|
Newly created memory cells are not initialized and therefore
|
|
|
|
|
they have a random value.
|
|
|
|
|
.IT 6.7.1
|
|
|
|
|
It shall be an error if
|
|
|
|
|
the value of any member denoted by any member-designator of the
|
|
|
|
|
set-constructor is outside the implementation-defined limits.
|
|
|
|
|
.IS
|
|
|
|
|
This error is detected (set bound error, trap 2, non-fatal).
|
|
|
|
|
.IT 6.7.1
|
|
|
|
|
It shall be an error if
|
|
|
|
|
the possible types of an set-constructor do not permit it
|
|
|
|
|
to assume a suitable type.
|
|
|
|
|
.IS
|
|
|
|
|
The compiler allocates as many bits as are necessary to store all
|
|
|
|
|
elements of the host-type of the base-type of the set, not the
|
|
|
|
|
base-type itself.
|
|
|
|
|
Therefore, all possible errors can be detected at compile time.
|
|
|
|
|
.IT 6.7.2.2
|
|
|
|
|
It shall be an error if j is zero in 'i div j'.
|
|
|
|
|
.IS
|
|
|
|
|
It depends on the EM implementation whether this error is detected:
|
|
|
|
|
.I1
|
|
|
|
|
\*(ONdetected (divide by 0, trap 6, non-fatal).
|
|
|
|
|
.br
|
|
|
|
|
\*(OFnot detected.
|
|
|
|
|
.I2
|
|
|
|
|
not detected.
|
|
|
|
|
.IE
|
|
|
|
|
.IT 6.7.2.2
|
|
|
|
|
It shall be an error if
|
|
|
|
|
j is zero or negative in i MOD j.
|
|
|
|
|
.IS
|
|
|
|
|
This error is detected (only positive j in 'i mod j', trap 71, non-fatal).
|
|
|
|
|
.IT 6.7.2.2
|
|
|
|
|
It shall be an error if the result of any operation on integer
|
|
|
|
|
operands is not performed according to the mathematical
|
|
|
|
|
rules for integer arithmetic.
|
|
|
|
|
.IS
|
|
|
|
|
The reaction depends on the EM implementation:
|
|
|
|
|
.I1
|
|
|
|
|
\*(ONerror detected if
|
|
|
|
|
.EQ
|
|
|
|
|
(result >= 32768) or (result < -32768).
|
|
|
|
|
.EN
|
|
|
|
|
(integer overflow, trap 3, non-fatal).
|
|
|
|
|
Note that if the result is -32768 the use of this value in further operations
|
|
|
|
|
may cause an error.
|
|
|
|
|
.br
|
|
|
|
|
\*(OFnot detected.
|
|
|
|
|
.I2
|
|
|
|
|
not detected.
|
|
|
|
|
.IT 6.8.3.5
|
|
|
|
|
It shall be an error if none of the case-constants is equal to the value of the
|
|
|
|
|
case-index upon entry to the case-statement.
|
|
|
|
|
.IS
|
|
|
|
|
This error is detected (case error, trap 20, fatal).
|
|
|
|
|
.IT 6.8.3.9
|
|
|
|
|
It shall be an error if the final-value of a for-statement is not
|
|
|
|
|
assignment-compatible with the control-variable when the
|
|
|
|
|
initial-value is assigned to the control-variable.
|
|
|
|
|
.IS
|
|
|
|
|
It is detected if the control variable leaves
|
|
|
|
|
its allowed range of values while stepping
|
|
|
|
|
from initial to final value.
|
|
|
|
|
This is equivalent with the requirements if the
|
|
|
|
|
for-statement is not terminated before
|
|
|
|
|
the final value is reached.
|
|
|
|
|
.IT 6.9.2
|
|
|
|
|
It shall be an error if the sequence of characters read looking for an integer does not
|
|
|
|
|
form a signed-integer as specified in 6.1.5.
|
|
|
|
|
.IS
|
|
|
|
|
This error is detected (digit expected, trap 105, non-fatal).
|
|
|
|
|
.IT 6.9.2
|
|
|
|
|
It shall be an error if the sequence of characters read looking for a real does not
|
|
|
|
|
form a signed-number as specified in 6.1.5.
|
|
|
|
|
.IS
|
|
|
|
|
This error is detected (digit expected, trap 105, non-fatal).
|
|
|
|
|
.IT 6.9.2
|
|
|
|
|
It shall be an error if read is applied to f while f is undefined or
|
|
|
|
|
not opened for reading.
|
|
|
|
|
.IS
|
|
|
|
|
This error is detected (see get(f)).
|
|
|
|
|
.IT 6.9.4
|
|
|
|
|
It shall be an error if write is applied to f while f is undefined or
|
|
|
|
|
not opened for writing.
|
|
|
|
|
.IS
|
|
|
|
|
This error is detected (see put(f)).
|
|
|
|
|
.IT 6.9.4
|
|
|
|
|
It shall be an error if TotalWidth or FracDigits as specified in
|
|
|
|
|
write or writeln procedure calls are less than one.
|
|
|
|
|
.IS
|
|
|
|
|
This error is not detected. Moreover, it is considered an extension to
|
|
|
|
|
allow zero or negative values.
|
|
|
|
|
.IT 6.9.6
|
|
|
|
|
It shall be an error if page is applied to f while f is undefined or
|
|
|
|
|
not opened for writing.
|
|
|
|
|
.IS
|
|
|
|
|
This error is detected (see put(f)).
|
|
|
|
|
.CH "Extensions to the standard"
|
|
|
|
|
.IS
|
|
|
|
|
.ti -3
|
|
|
|
|
1.~\
|
|
|
|
|
Separate compilation.
|
|
|
|
|
.sp
|
|
|
|
|
The compiler is able to (separately) compile a collection of declarations,
|
|
|
|
|
procedures and functions to form a library.
|
|
|
|
|
The library may be linked with the main program, compiled later.
|
|
|
|
|
The syntax of these modules is
|
|
|
|
|
.EQ
|
|
|
|
|
module = [constant-definition-part]
|
|
|
|
|
[type-definition-part]
|
|
|
|
|
[var-declaration-part]
|
|
|
|
|
[procedure-and-function-declaration-part]
|
|
|
|
|
.EN
|
|
|
|
|
The compiler accepts a program or a module:
|
|
|
|
|
.EQ
|
|
|
|
|
unit = program | module
|
|
|
|
|
.EN
|
|
|
|
|
All variables declared outside a module must be imported
|
|
|
|
|
by parameters, even the files input and output.
|
|
|
|
|
Access to a variable declared in a module is only possible
|
|
|
|
|
using the procedures and functions declared in that same module.
|
|
|
|
|
By giving the correct procedure/function heading followed by the
|
|
|
|
|
directive 'extern' you may use procedures and functions declared in
|
|
|
|
|
other units.
|
|
|
|
|
.sp
|
|
|
|
|
.ti -3
|
|
|
|
|
2.~\
|
|
|
|
|
Assertions.
|
|
|
|
|
.sp
|
|
|
|
|
The Ack-Pascal compiler recognizes an additional statement, the assertion.
|
|
|
|
|
Assertions can be used as an aid in debugging and documentation.
|
|
|
|
|
The syntax is:
|
|
|
|
|
.EQ
|
|
|
|
|
assertion = 'assert' Boolean-expression
|
|
|
|
|
.EN
|
|
|
|
|
An assertion is a simple-statement, so
|
|
|
|
|
.EQ
|
|
|
|
|
simple-statement = [assignment-statement |
|
|
|
|
|
procedure-statement |
|
|
|
|
|
goto-statement |
|
|
|
|
|
assertion
|
|
|
|
|
]
|
|
|
|
|
.EN
|
|
|
|
|
An assertion causes an error if the Boolean-expression is false.
|
|
|
|
|
That is its only purpose.
|
|
|
|
|
It does not change any of the variables, at least it should not.
|
|
|
|
|
Therefore, do not use functions with side-effects in the Boolean-expression.
|
|
|
|
|
If the a-option is turned off, then assertions are skipped by the
|
|
|
|
|
compiler. 'assert' is not a word-symbol (keyword) and may be used as identifier.
|
|
|
|
|
However, assignment to a variable and calling of a procedure with that name will be impossible.
|
|
|
|
|
.sp
|
|
|
|
|
.ti -3
|
|
|
|
|
3.~\
|
|
|
|
|
Additional procedures.
|
|
|
|
|
.sp
|
|
|
|
|
Three additional standard procedures are available:
|
|
|
|
|
.IS
|
|
|
|
|
.IS
|
|
|
|
|
.ti -8
|
|
|
|
|
halt:~~~a call of this procedure is equivalent to jumping to the
|
|
|
|
|
end of your program. It is always the last statement executed.
|
|
|
|
|
The exit status of the program may be supplied
|
|
|
|
|
as optional argument.
|
|
|
|
|
.ti -8
|
|
|
|
|
release:
|
|
|
|
|
.ti -8
|
|
|
|
|
mark:~~~for most applications it is sufficient to use the heap as second stack.
|
|
|
|
|
Mark and release are suited for this type of use, more suited than dispose.
|
|
|
|
|
mark(p), with p of type pointer, stores the current value of the
|
|
|
|
|
heap pointer in p. release(p), with p initialized by a call
|
|
|
|
|
of mark(p), restores the heap pointer to its old value.
|
|
|
|
|
All the heap objects, created by calls of new between the call of
|
|
|
|
|
mark and the call of release, are removed and the space they used
|
|
|
|
|
can be reallocated.
|
|
|
|
|
Never use mark and release together with dispose!
|
|
|
|
|
.sp
|
|
|
|
|
.in -10
|
|
|
|
|
.ti -3
|
|
|
|
|
4.~\
|
|
|
|
|
UNIX interfacing.
|
|
|
|
|
.sp
|
|
|
|
|
If the c-option is turned on, then some special features are available
|
|
|
|
|
to simplify an interface with the UNIX environment.
|
|
|
|
|
First of all, the compiler allows you to use a different type
|
|
|
|
|
of string constants.
|
|
|
|
|
These string constants are delimited by double quotes ('"').
|
|
|
|
|
To put a double quote into these strings, you must repeat the double quote,
|
|
|
|
|
like the single quote in normal string constants.
|
|
|
|
|
These special string constants are terminated by a zero byte (chr(0)).
|
|
|
|
|
The type of these constants is a pointer to a packed array of characters,
|
|
|
|
|
with lower bound 1 and unknown upper bound.
|
|
|
|
|
.br
|
|
|
|
|
Secondly, the compiler predefines a new type identifier 'string' denoting
|
|
|
|
|
this just described string type.
|
|
|
|
|
.PP
|
|
|
|
|
The only thing you can do with these features is declaration of
|
|
|
|
|
constants and variables of type 'string'.
|
|
|
|
|
String objects may not be allocated on the heap and string pointers
|
|
|
|
|
may not be de-referenced.
|
|
|
|
|
Still these strings are very useful in combination with external routines.
|
|
|
|
|
The procedure write is extended to print these zero-terminated strings correctly.
|
|
|
|
|
.sp
|
|
|
|
|
.ti -3
|
|
|
|
|
5.~\
|
|
|
|
|
Double length (32 bit) integers.
|
|
|
|
|
.sp
|
|
|
|
|
If the d-option is turned on, then the additional type 'long' is known to the compiler.
|
|
|
|
|
Long variables have integer values in the range -2147483647..+2147483647.
|
|
|
|
|
Long constants may be declared.
|
|
|
|
|
It is not allowed to form subranges of type long.
|
|
|
|
|
All operations allowed on integers are also
|
|
|
|
|
allowed on longs and are indicated by the same
|
|
|
|
|
operators: '+', '-', '*', '/', 'div', 'mod'.
|
|
|
|
|
The procedures read and write have been extended to handle long arguments correctly.
|
|
|
|
|
The default width for longs is 11.
|
|
|
|
|
The standard procedures 'abs' and 'sqr' have been extended to work on long arguments.
|
|
|
|
|
Conversion from integer to long, long to real,
|
|
|
|
|
real to long and long to integer are automatic, like the conversion from integer to real.
|
|
|
|
|
These conversions may cause a
|
|
|
|
|
.IS
|
|
|
|
|
conversion error, trap 10, non-fatal
|
|
|
|
|
.IE
|
|
|
|
|
This last error is only detected in implementation 1, with 'test on'.
|
|
|
|
|
Note that all current implementations use target
|
|
|
|
|
machine floating point instructions
|
|
|
|
|
to perform some of the long operations.
|
|
|
|
|
.sp
|
|
|
|
|
.ti -3
|
|
|
|
|
6.~\
|
|
|
|
|
Underscore as letter.
|
|
|
|
|
.sp
|
|
|
|
|
The character '_' may be used in forming identifiers, if the u-option is turned on.
|
|
|
|
|
.sp
|
|
|
|
|
.ti -3
|
|
|
|
|
7.~\
|
|
|
|
|
Zero field width in write.
|
|
|
|
|
.sp
|
|
|
|
|
Zero or negative TotalWidth arguments to write
|
|
|
|
|
are allowed.
|
|
|
|
|
No characters are written for character, string or Boolean type arguments then.
|
|
|
|
|
A zero or negative FracDigits argument for fixed-point representation of reals causes the
|
|
|
|
|
fraction and the character '.' to be suppressed.
|
|
|
|
|
.sp
|
|
|
|
|
.ti -3
|
|
|
|
|
8.~\
|
|
|
|
|
Alternate symbol representation.
|
|
|
|
|
.sp
|
|
|
|
|
The comment delimiters '(*' and '*)' are recognized and treated like '{' and '}'.
|
|
|
|
|
The other alternate representations of symbols are not recognized.
|
|
|
|
|
.CH "Deviations from the standard"
|
|
|
|
|
Ack-Pascal deviates from the (March 1980) standard proposal in the following ways:
|
|
|
|
|
.IS
|
|
|
|
|
.ti -3
|
|
|
|
|
1.~\
|
|
|
|
|
Only the first 8 characters of identifiers are significant,
|
|
|
|
|
as requested by all standard proposals prior to March 1980.
|
|
|
|
|
In that proposal, however, the sentence
|
|
|
|
|
.DS
|
|
|
|
|
"A conforming program should not have its meaning altered
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by the truncation of its identifiers to eight characters
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or the truncation of its labels to four digits."
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.DE
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is missing.
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.sp
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.ti -3
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2.~\
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The character sequences 'procedur', 'procedur8', 'functionXyZ' etc. are
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all erroneously classified as the word-symbols 'procedure' and 'function'.
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.sp
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.ti -3
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3.~\
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Standard procedures and functions are not allowed as parameters in Ack-Pascal,
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conforming to all previous standard proposals.
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You can obtain the same result with negligible loss of performance
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by declaring some user routines like:
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.EQ
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function sine(x:real):real;
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begin
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sine:=sin(x)
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end;
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.EN
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.sp
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.ti -3
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4.~\
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The scope of identifiers and labels should start at the beginning of the block
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in which these identifiers or labels are declared.
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The Ack-Pascal compiler, as most other one pass compilers, deviates in this respect,
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because the scope of variables and labels start
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at their defining-point.
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.CH "Compiler options"
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Some options of the compiler may be controlled by using "{$....}".
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Each option consists of a lower case letter followed by +, - or an unsigned
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number.
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Options are separated by commas.
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The following options exist:
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.in 8
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.sp
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.ti -8
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a~+/-~~~\
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this option switches assertions on and off.
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If this option is on, then code is included to test these assertions
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at run time. Default +.
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.sp
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.ti -8
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c~+/-~~~\
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this option, if on, allows you to use C-type string constants
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surrounded by double quotes.
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Moreover, a new type identifier 'string' is predefined.
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Default -.
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.sp
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.ti -8
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d~+/-~~~\
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this option, if on, allows you to use variables of type 'long'.
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Default -.
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.sp
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.ti -8
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f~<num>~\
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the size of reals can be changed by this option. <num> should be specified in 8-bit bytes.
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The default in most implementations is 8, but other values can
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occur.
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.sp
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.ti -8
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i~<num>~\
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with this flag the setsize for a set of integers can be
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manipulated.
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The number must be the number of bits per set.
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The default value is 16, just fitting in one word on the PDP and many other minis.
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.sp
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.ti -8
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l~+/-~~~\
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if + then code is inserted to keep track of the source line number.
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When this flag is switched on and off, an incorrect line number may appear
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if the error occurs in a part of your program for which this flag is off.
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These same line numbers are used for the profile, flow and count options
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of the EM interpreter em [6].
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Default +.
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.sp
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.ti -8
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p~<num>~the size of pointers can be changed by this option. <num> should be specified in bytes.
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Default 2 in most implementations.
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.sp
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.ti -8
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r~+/-~~~\
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if + then code is inserted to check subrange variables against
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lower and upper subrange limits.
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Default +.
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.sp
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.ti -8
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s~+/-~~~\
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if + then the compiler will hunt for places in your program
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where non-standard features are used, and for each place found
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it will generate a warning. Default -.
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.sp
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.ti -8
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t~+/-~~~\
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if + then each time a procedure is entered, the routine 'procentry'
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is called.
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The compiler checks this flag just before the first symbol that follows the
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first 'begin' of the body of the procedure.
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Also, when the procedure exits, then the procedure 'procexit' is called
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|
if the t flag is on just before the last 'end' of the procedure body.
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|
Both 'procentry' and 'procexit' have a packed array of 8 characters as a parameter.
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|
Default procedures are present in the run time library.
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|
Default -.
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.sp
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.ti -8
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|
u~+/-~~~\
|
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|
if + then the character '_' is treated like a lower case letter,
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|
so that it may be used in identifiers.
|
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|
|
Procedure and function identifiers starting with an underscore may cause problems,
|
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|
|
because they may collide with library routine names.
|
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|
|
Default -.
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|
.in 0
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.sp
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|
Seven of these flags (c, d, f, i, p, s and u) are only effective when they appear
|
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|
before the 'program' symbol. The others may be switched on and off.
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|
.PP
|
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|
|
A second method of passing options to the compiler ia available.
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|
|
This method uses the file on which the compact EM code will be written.
|
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|
|
The compiler starts reading from this file scanning for options
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|
in the same format as used normally, except for the comment delimiters and
|
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|
|
the dollar sign.
|
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|
|
All options found on the file override the options set in your program.
|
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|
|
Note that the compact code file must always exist before the compiler is called.
|
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|
.PP
|
|
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|
|
The user interface program \fIack\fP[4]
|
|
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|
|
takes care of creating this file normally
|
|
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|
|
and also writes one of its options onto this file.
|
|
|
|
|
The user can specify, for instance, without changing any character in its
|
|
|
|
|
Pascal program, that the compiler must include code for
|
|
|
|
|
procedure/function tracing.
|
|
|
|
|
.PP
|
|
|
|
|
Another very powerful debugging tool is the knowledge that inaccessible
|
|
|
|
|
statements and useless tests are removed by the EM optimizer.
|
|
|
|
|
For instance, a statement like:
|
|
|
|
|
.sp
|
|
|
|
|
.nf
|
|
|
|
|
if debug then
|
|
|
|
|
writeln('initialization done');
|
|
|
|
|
.fi
|
|
|
|
|
.sp
|
|
|
|
|
is completely removed by the optimizer if debug is a constant with
|
|
|
|
|
value false.
|
|
|
|
|
The first line is removed if debug is a constant with value true.
|
|
|
|
|
Of course, if debug is a variable nothing can be removed.
|
|
|
|
|
.PP
|
|
|
|
|
A disadvantage of Pascal, the lack of preinitialized data, can be
|
|
|
|
|
diminished by making use of the possibilities of the EM optimizer.
|
|
|
|
|
For instance, initializing an array of reserved words is sometimes
|
|
|
|
|
optimized into 3 EM instructions. To maximize this effect you must initialize
|
|
|
|
|
variables as much as possible in order of declaration and array entries
|
|
|
|
|
in order of decreasing index.
|
|
|
|
|
.CH "References"
|
|
|
|
|
.in +5
|
|
|
|
|
.ti -5
|
|
|
|
|
[1]~~\
|
|
|
|
|
ISO standard proposal ISO/TC97/SC5-N462, dated February 1979.
|
|
|
|
|
The same proposal, in slightly modified form, can be found in:
|
|
|
|
|
A.M.Addyman e.a., "A draft description of Pascal",
|
|
|
|
|
Software, practice and experience, May 1979.
|
|
|
|
|
An improved version, received March 1980,
|
|
|
|
|
is followed as much as possible for the
|
|
|
|
|
current Ack-Pascal.
|
|
|
|
|
.sp
|
|
|
|
|
.ti -5
|
|
|
|
|
[2]~~\
|
|
|
|
|
A.S.Tanenbaum, J.W.Stevenson, Hans van Staveren, E.G.Keizer,
|
|
|
|
|
"Description of a machine architecture for use with block structured languages",
|
|
|
|
|
Informatica rapport IR-81.
|
|
|
|
|
.sp
|
|
|
|
|
.ti -5
|
|
|
|
|
[3]~~\
|
|
|
|
|
W.S.Brown, S.I.Feldman, "Environment parameters and basic functions
|
|
|
|
|
for floating-point computation",
|
|
|
|
|
Bell Laboratories CSTR #72.
|
|
|
|
|
.sp
|
|
|
|
|
.ti -5
|
|
|
|
|
[4]~~\
|
|
|
|
|
UNIX manual ack(I).
|
|
|
|
|
.sp
|
|
|
|
|
.ti -5
|
|
|
|
|
[5]~~\
|
|
|
|
|
UNIX manual ld(I).
|
|
|
|
|
.sp
|
|
|
|
|
.ti -5
|
|
|
|
|
[6]~~\
|
|
|
|
|
UNIX manual em(I).
|
|
|
|
|
.sp
|
|
|
|
|
.ti -5
|
|
|
|
|
[7]~~\
|
|
|
|
|
UNIX manual libpc(VII)
|
|
|
|
|
.sp
|
|
|
|
|
.ti -5
|
|
|
|
|
[8]~~\
|
|
|
|
|
UNIX manual pc_prlib(VII)
|