118 lines
3.4 KiB
Text
118 lines
3.4 KiB
Text
.sp 2
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.NH
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Deviations from the standard
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.nh
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.PP
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The compiler deviates from the ISO 7185 standard with respect to the
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following clauses:
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.IP "\fBISO 6.1.3:\fR" 14
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\h'-5u'Identifiers may be of any length and all characters of an identifier
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shall be significant in distinguishing between them.
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.sp
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.in +3m
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The constant IDFSIZE, defined in the file \fIidfsize.h\fR, determines
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the (maximum) significant length of an identifier. It can be set at run
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time with the \-M option (see also section on compiler options).
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.in -3m
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.sp
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.IP "\fBISO 6.1.8:\fR"
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\h'-5u'There shall be at least one separator between any pair of consecutive tokens
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made up of identifiers, word-symbols, labels or unsigned-numbers.
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.sp
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.in +3m
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A token separator is not needed when a number is followed by an identifier
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or a word-symbol. For example the input sequence, 2\fBthen\fR, is recognized
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as the integer 2 followed by the keyword \fBthen\fR.
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.in -3m
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.sp
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.IP "\fBISO 6.2.1:\fR"
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\h'-29u'The label-declaration-part shall specify all labels that prefix a statement
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in the corresponding statement-part.
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.sp
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.ti +3m
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The compiler generates a warning if a label is declared but never defined.
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.bp
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.IP "\fBISO 6.2.2:\fR"
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\h'-9u'The scope of identifiers and labels should start at the beginning of the
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block in which these identifiers or labels are declared.
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.sp
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.in +3m
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The compiler, as most other one pass compilers deviates in this respect,
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because the scope of variables and labels start at their defining-point.
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.nf
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.in +4m
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\fBprogram\fR deviates\fB;
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const\fR
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x \fB=\fR 3\fB;
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procedure\fR p\fB;
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const\fR
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y \fB=\fR x\fB;\fR
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x \fB=\fR true\fB;
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begin end;
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begin
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end.\fR
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.in -4m
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.fi
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In procedure p, the constant y has the integer value 3. This program does not
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conform to the standard. In [SAL] a simple algorithm is described for
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enforcing the scope rules, it involves numbering all scopes encoutered in the
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program in order of their opening, and recording in each identifier table
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entry the number of the latest scope in which it is used.
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Note: The compiler does not deviate from the standard in the following program:
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.nf
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.in +4m
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\fBprogram\fR conforms\fB;
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type\fR
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x \fB=\fR real\fB;
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procedure\fR p\fB;
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type\fR
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y \fB= ^\fRx\fB;\fR
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x \fB=\fR boolean\fB;
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var\fR
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p \fB:\fR y\fB;
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begin end;
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begin
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end.\fR
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.in -4m
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.fi
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In procedure p, the variable p is a pointer to boolean.
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.fi
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.in -3m
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.sp
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.IP "\fBISO 6.4.3.2:\fR"
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The standard specifies that any ordinal type is allowed as index-type.
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.sp
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.in +3m
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The required type \fIinteger\fR is not allowed as index-type, i.e.
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.ti +2m
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\fBARRAY [ \fIinteger\fB ] OF\fR <component-type>
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is not permitted.
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.br
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This could be implemented, but this might cause problems on machines with
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a small memory.
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.in -3m
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.sp
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.IP "\fBISO 6.4.3.3:\fR"
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\h'-1u'The type possessed by the variant-selector, called the tag-type, must
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be an ordinal type, so the integer type is permitted. The values denoted by
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all case-constants shall be distinct and the set thereof shall be equal
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to the set of values specified by the tag-type.
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.sp
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.in +3m
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Because it is impracticable to enumerate all integers as case-constants,
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the integer type is not permitted as tag-type. It would not make a great
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difference to allow it as tagtype.
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.in -3m
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.sp
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.IP "\fBISO 6.8.3.9:\fR"
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The standard specifies that the control-variable of a for-statement is not
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allowed to be modified while executing the loop.
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.sp
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.in +3m
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Violation of this rule is not detected. An algorithm to implement this rule
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can be found in [PCV].
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