Some corrections
This commit is contained in:
ceriel
parent
715dd4ef0f
commit
8ffaf72dfa
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@ -311,7 +311,7 @@ call name (acc, cc, apc or pc) or by the \fB\-.suffix\fP flag.
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.IP \fIneed\fP
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.br
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This \-~optional~\- keyword indicates that the rest of the line must be
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concatenated to the NEEDS variable.
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concatenated to the HEAD and TAIL variables.
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This is done once for every transformation used or indicated
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by one of the program call names mentioned above or indicated
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by the \fB\-.suffix\fP flag.
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326
doc/m2ref.doc
326
doc/m2ref.doc
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@ -15,28 +15,41 @@ The Netherlands
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Introduction
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.PP
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This document describes the implementation-specific features of the
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ACK Modula-2 compiler. It is not intended to teach Modula-2 programming.
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For a description of the Modula-2 language, the reader is referred to [1].
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ACK Modula-2 compiler.
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It is not intended to teach Modula-2 programming.
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For a description of the Modula-2 language,
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the reader is referred to [1].
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.PP
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The ACK Modula-2 compiler is currently available for use with the VAX,
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Motorola MC68020, Motorola MC68000,
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PDP-11, and Intel 8086 code-generators.
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For the 8086, MC68000, and MC68020,
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floating point emulation is used. This is made available with the \fI-fp\fP
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option, which must be passed to \fIack\fP[4,5].
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Motorola MC68020,
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Motorola MC68000,
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PDP-11,
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and Intel 8086 code-generators.
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For the 8086,
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MC68000,
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and MC68020,
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floating point emulation is used.
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This is made available with the \fI-fp\fP
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option,
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which must be passed to \fIack\fP[4,5].
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.NH
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The language implemented
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.PP
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This section discusses the deviations from the Modula-2 language as described
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in the "Report on The Programming Language Modula-2", as it appeared in [1],
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in the "Report on The Programming Language Modula-2",
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as it appeared in [1],
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from now on referred to as "the Report".
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Also, the Report sometimes leaves room for interpretation. The section numbers
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Also,
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the Report sometimes leaves room for interpretation.
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The section numbers
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mentioned are the section numbers of the Report.
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.NH 2
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Syntax (section 2)
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.PP
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The syntax recognized is that of the Report, with some extensions to
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also recognize the syntax of an earlier definition, given in [2].
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The syntax recognized is that of the Report,
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with some extensions to
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also recognize the syntax of an earlier definition,
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given in [2].
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Only one compilation unit per file is accepted.
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.NH 2
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Vocabulary and Representation (section 3)
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@ -51,8 +64,10 @@ ARRAY [0 .. 0] OF CHAR
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.DE
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and contains one character: \f(CW0C\fP.
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.PP
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When the text of a comment starts with a '\f(CW$\fP', it may be a pragma.
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Currently, the following pragmas exist:
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When the text of a comment starts with a '\f(CW$\fP',
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it may be a pragma.
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Currently,
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the following pragmas exist:
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.DS
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.ft CW
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(*$F (F stands for Foreign) *)
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@ -64,52 +79,81 @@ Currently, the following pragmas exist:
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The Foreign pragma is only meaningful in a \f(CWDEFINITION MODULE\fP,
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and indicates that this
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\f(CWDEFINITION MODULE\fP describes an interface to a module written in another
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language (for instance C, Pascal, or EM).
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language (for instance C,
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Pascal,
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or EM).
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Runtime checks that can be disabled are:
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range checks,
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\f(CWCARDINAL\fP overflow checks,
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checks when assigning a \f(CWCARDINAL\fP to an \f(CWINTEGER\fP and vice versa,
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and checks that \f(CWFOR\fP-loop control-variables are not changed
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in the body of the loop.
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Array bound checks can be enabled, because many EM implementations do not
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Array bound checks can be enabled,
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because many EM implementations do not
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implement the array bound checking of the EM array instructions.
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When enabled, the compiler generates a check before generating an
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When enabled,
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the compiler generates a check before generating an
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EM array instruction.
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Even when underscores are enabled, they still may not start an identifier.
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Even when underscores are enabled,
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they still may not start an identifier.
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.PP
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Constants of type \f(CWLONGINT\fP are integers with a suffix letter \f(CWD\fP
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(for instance \f(CW1987D\fP).
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Constants of type \f(CWLONGREAL\fP have suffix \f(CWD\fP if a scale factor is missing,
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or have \f(CWD\fP in place of \f(CWE\fP in the scale factor (f.i. \f(CW1.0D\fP,
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\f(CW0.314D1\fP).
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This addition was made, because there was no way to indicate long constants,
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This addition was made,
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because there was no way to indicate long constants,
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and also because the addition was made in Wirth's newest Modula-2 compiler.
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.NH 2
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Declarations and scope rules (section 4)
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.PP
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Standard identifiers are considered to be predeclared, and valid in all
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parts of a program. They are called \fIpervasive\fP.
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Unfortunately, the Report does not state how this pervasiveness is accomplished.
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However, page 87 of [1] states: "Standard identifiers are automatically
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imported into all modules". Our implementation therefore allows
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redeclarations of standard identifiers within procedures, but not within
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Standard identifiers are considered to be predeclared,
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and valid in all
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parts of a program.
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They are called \fIpervasive\fP.
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Unfortunately,
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the Report does not state how this pervasiveness is accomplished.
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However,
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page 87 of [1] states: "Standard identifiers are automatically
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imported into all modules".
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Our implementation therefore allows
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redeclarations of standard identifiers within procedures,
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but not within
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modules.
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.NH 2
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Constant expressions (section 5)
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.PP
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Each operand of a constant expression must be a constant:
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a string, a number, a set, an enumeration literal, a qualifier denoting a
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constant expression, a typetransfer with a constant argument, or
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one of the standard procedures
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\f(CWABS\fP, \f(CWCAP\fP, \f(CWCHR\fP, \f(CWLONG\fP, \f(CWMAX\fP, \f(CWMIN\fP,
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\f(CWODD\fP, \f(CWORD\fP,
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\f(CWSIZE\fP, \f(CWSHORT\fP, \f(CWTSIZE\fP, or \f(CWVAL\fP, with constant argument(s);
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a string,
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a number,
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a set,
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an enumeration literal,
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a qualifier denoting a
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constant expression,
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a type transfer with a constant argument,
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or one of the standard procedures
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\f(CWABS\fP,
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\f(CWCAP\fP,
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\f(CWCHR\fP,
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\f(CWLONG\fP,
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\f(CWMAX\fP,
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\f(CWMIN\fP,
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\f(CWODD\fP,
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\f(CWORD\fP,
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\f(CWSIZE\fP,
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\f(CWSHORT\fP,
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\f(CWTSIZE\fP,
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or \f(CWVAL\fP,
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with constant argument(s);
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\f(CWTSIZE\fP and \f(CWSIZE\fP may also have a variable as argument.
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.PP
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Floating point expressions are never evaluated compile time, because
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the compiler basically functions as a cross-compiler, and thus cannot
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Floating point expressions are never evaluated compile time,
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because the compiler basically functions as a cross-compiler,
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and thus cannot
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use the floating point instructions of the machine on which it runs.
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Also, \f(CWMAX(REAL)\fP and \f(CWMIN(REAL)\fP are not allowed.
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Also,
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\f(CWMAX(REAL)\fP and \f(CWMIN(REAL)\fP are not allowed.
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.NH 2
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Type declarations (section 6)
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.NH 3
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@ -117,7 +161,8 @@ Basic types (section 6.1)
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.PP
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The type \f(CWCHAR\fP includes the ASCII character set as a subset.
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Values range from
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\f(CW0C\fP to \f(CW377C\fP, not from \f(CW0C\fP to \f(CW177C\fP.
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\f(CW0C\fP to \f(CW377C\fP,
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not from \f(CW0C\fP to \f(CW177C\fP.
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.NH 3
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Enumerations (section 6.2)
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.PP
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@ -127,16 +172,22 @@ is \f(CWMAX(INTEGER)\fP.
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Record types (section 6.5)
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.PP
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The syntax of variant sections in [1] is different from the one in [2].
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Our implementation recognizes both, giving a warning for the older one.
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However, see section 3.
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Our implementation recognizes both,
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giving a warning for the older one.
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However,
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see section 3.
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.NH 3
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Set types (section 6.6)
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.PP
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The only limitation imposed by the compiler is that the base type of the
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set must be a subrange type, an enumeration type, \f(CWCHAR\fP, or
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\f(CWBOOLEAN\fP.
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So, the lower bound may be negative.
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However, if a negative lower bound is used,
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set must be a subrange type,
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an enumeration type,
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\f(CWCHAR\fP,
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or \f(CWBOOLEAN\fP.
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So,
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the lower bound may be negative.
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However,
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if a negative lower bound is used,
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the compiler gives a warning of the \fIrestricted\fP class (see the manual
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page of the compiler).
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.PP
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@ -173,26 +224,30 @@ or
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(-1) + 1
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.ft P
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.DE
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I have seen some compilers that implement the first alternative, and others
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that implement the second. Our compiler implements the second, which is
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suggested by the fact that their priority is not specified, which might
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indicate that it is the same as that of their binary counterparts.
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I have seen some compilers that implement the first alternative,
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and others that implement the second.
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Our compiler implements the second,
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which is suggested by the fact that their priority is not specified,
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which might indicate that it is the same as that of their binary counterparts.
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And then the rule about left to right decides for the second.
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On the other hand, one might argue that, since the grammar only allows
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for one unary operator in a simple expression, it must apply to the
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whole simple expression, not just the first term.
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On the other hand one might argue that,
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since the grammar only allows for one unary operator in a simple expression,
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it must apply to the whole simple expression,
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not just the first term.
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.NH 2
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Statements (section 9)
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.NH 3
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Assignments (section 9.1)
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.PP
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The Report does not define the evaluation order in an assignment.
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||||
Our compiler certainly chooses an evaluation order, but it is explicitly
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left undefined. Therefore, programs that depend on it, may cease to
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work later.
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Our compiler certainly chooses an evaluation order,
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but it is explicitly left undefined.
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Therefore,
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programs that depend on it may cease to work later.
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.PP
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The types \f(CWINTEGER\fP and \f(CWCARDINAL\fP are assignment-compatible with
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\f(CWLONGINT\fP, and \f(CWREAL\fP is assignment-compatible with \f(CWLONGREAL\fP.
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\f(CWLONGINT\fP,
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and \f(CWREAL\fP is assignment-compatible with \f(CWLONGREAL\fP.
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.NH 3
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Case statements (section 9.5)
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.PP
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@ -200,14 +255,17 @@ The size of the type of the case-expression must be less than or equal to
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the word-size.
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.PP
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The Report does not specify what happens if the value of the case-expression
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does not occur as a label of any case, and there is no \f(CWELSE\fP-part.
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In our implementation, this results in a runtime error.
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does not occur as a label of any case,
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and there is no \f(CWELSE\fP-part.
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In our implementation,
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||||
this results in a runtime error.
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.NH 3
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For statements (section 9.8)
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.PP
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||||
The Report does not specify the legal types for a control variable.
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||||
Our implementation allows the basic types (except \f(CWREAL\fP),
|
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enumeration types, and subranges.
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enumeration types,
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and subranges.
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||||
A runtime warning is generated when the value of the control variable
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||||
is changed by the statement sequence that forms the body of the loop,
|
||||
unless runtime checking is disabled.
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||||
|
|
@ -219,82 +277,105 @@ Our implementation allows any result type.
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.NH 2
|
||||
Procedure declarations (section 10)
|
||||
.PP
|
||||
Function procedures must exit through a RETURN statement, or a runtime error
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||||
occurs.
|
||||
Function procedures must exit through a RETURN statement,
|
||||
or a runtime error occurs.
|
||||
.NH 3
|
||||
Standard procedures (section 10.2)
|
||||
.PP
|
||||
Our implementation supports \f(CWNEW\fP and \f(CWDISPOSE\fP
|
||||
for backwards compatibility,
|
||||
but issues warnings for their use. However, see section 3.
|
||||
but issues warnings for their use.
|
||||
However,
|
||||
see section 3.
|
||||
.PP
|
||||
Also, some new standard procedures were added, similar to the new standard
|
||||
procedures in Wirth's newest compiler:
|
||||
Also,
|
||||
some new standard procedures were added,
|
||||
similar to the new standard procedures in Wirth's newest compiler:
|
||||
.IP \-
|
||||
\f(CWLONG\fP converts an argument of type \f(CWINTEGER\fP or \f(CWREAL\fP to the
|
||||
types \f(CWLONGINT\fP or \f(CWLONGREAL\fP.
|
||||
.IP \-
|
||||
\f(CWSHORT\fP performs the inverse transformation, without range checks.
|
||||
\f(CWSHORT\fP performs the inverse transformation,
|
||||
without range checks.
|
||||
.IP \-
|
||||
\f(CWFLOATD\fP is analogous to \f(CWFLOAT\fP, but yields a result of type
|
||||
\f(CWFLOATD\fP is analogous to \f(CWFLOAT\fP,
|
||||
but yields a result of type
|
||||
\f(CWLONGREAL\fP.
|
||||
.IP \-
|
||||
\f(CWTRUNCD\fP is analogous to \f(CWTRUNC\fP, but yields a result of type
|
||||
\f(CWTRUNCD\fP is analogous to \f(CWTRUNC\fP,
|
||||
but yields a result of type
|
||||
\f(CWLONGINT\fP.
|
||||
.NH 2
|
||||
System-dependent facilities (section 12)
|
||||
.PP
|
||||
The type \f(CWBYTE\fP is added to the \f(CWSYSTEM\fP module.
|
||||
It occupies a storage unit of 8 bits.
|
||||
\f(CWARRAY OF BYTE\fP has a similar effect to \f(CWARRAY OF WORD\fP, but is
|
||||
safer. In some obscure cases the \f(CWARRAY OF WORD\fP mechanism does not quite
|
||||
\f(CWARRAY OF BYTE\fP has a similar effect to \f(CWARRAY OF WORD\fP,
|
||||
but is safer.
|
||||
In some obscure cases the \f(CWARRAY OF WORD\fP mechanism does not quite
|
||||
work properly.
|
||||
.PP
|
||||
The procedure \f(CWIOTRANSFER\fP is not implemented.
|
||||
.NH 1
|
||||
Backwards compatibility
|
||||
.PP
|
||||
Besides recognizing the language as described in [1], the compiler recognizes
|
||||
most of the language described in [2], for backwards compatibility.
|
||||
Besides recognizing the language as described in [1],
|
||||
the compiler recognizes most of the language described in [2],
|
||||
for backwards compatibility.
|
||||
It warns the user for old-fashioned
|
||||
constructions (constructions that [1] does not allow).
|
||||
If the \fI-Rm2-3\fP option (see [6]) is passed to \fIack\fP, this backwards
|
||||
compatibility feature is disabled. Also, it may not be present on some
|
||||
smaller machines, like the PDP-11.
|
||||
If the \fI-Rm2-3\fP option (see [6]) is passed to \fIack\fP,
|
||||
this backwards compatibility feature is disabled.
|
||||
Also,
|
||||
it may not be present on some
|
||||
smaller machines,
|
||||
like the PDP-11.
|
||||
.NH 1
|
||||
Compile time errors
|
||||
.PP
|
||||
The compile time error messages are intended to be self-explanatory,
|
||||
and not listed here. The compiler also sometimes issues warnings,
|
||||
and not listed here.
|
||||
The compiler also sometimes issues warnings,
|
||||
recognizable by a warning-classification between parentheses.
|
||||
Currently, there are 3 classifications:
|
||||
Currently,
|
||||
there are 3 classifications:
|
||||
.IP "(old-fashioned use)"
|
||||
.br
|
||||
These warnings are given on constructions that are not allowed by [1], but are
|
||||
allowed by [2].
|
||||
These warnings are given on constructions that are not allowed by [1],
|
||||
but are allowed by [2].
|
||||
.IP (strict)
|
||||
.br
|
||||
These warnings are given on constructions that are supported by the
|
||||
ACK Modula-2 compiler, but might not be supported by others.
|
||||
Examples: functions returning structured types, SET types of subranges with
|
||||
These warnings are given on constructions that are supported by the
|
||||
ACK Modula-2 compiler,
|
||||
but might not be supported by others.
|
||||
Examples: functions returning structured types,
|
||||
SET types of subranges with
|
||||
negative lower bound.
|
||||
.IP (warning)
|
||||
.br
|
||||
The other warnings, such as warnings about variables that are never assigned,
|
||||
never used, etc.
|
||||
The other warnings,
|
||||
such as warnings about variables that are never assigned,
|
||||
never used,
|
||||
etc.
|
||||
.NH 1
|
||||
Runtime errors
|
||||
.PP
|
||||
The ACK Modula-2 compiler produces code for an EM machine as defined in [3].
|
||||
Therefore, it depends on the implementation
|
||||
Therefore,
|
||||
it depends on the implementation
|
||||
of the EM machine for detection some of the runtime errors that could occur.
|
||||
.PP
|
||||
The \fITraps\fP module enables the user to install his own runtime
|
||||
error handler.
|
||||
The default one just displays what happened and exits.
|
||||
Basically, a trap handler is just a procedure that takes an INTEGER as
|
||||
parameter. The INTEGER is the trap number. This INTEGER can be one of the
|
||||
EM trap numbers, listed in [3], or one of the numbers listed in the
|
||||
Basically,
|
||||
a trap handler is just a procedure that takes an INTEGER as
|
||||
parameter.
|
||||
The INTEGER is the trap number.
|
||||
This INTEGER can be one of the
|
||||
EM trap numbers,
|
||||
listed in [3],
|
||||
or one of the numbers listed in the
|
||||
\fITraps\fP definition module.
|
||||
.PP
|
||||
The following runtime errors may occur:
|
||||
|
|
@ -303,7 +384,8 @@ The following runtime errors may occur:
|
|||
The detection of this error depends on the EM implementation.
|
||||
.IP "range bound error"
|
||||
.br
|
||||
Range bound errors are always detected, unless runtime checks are disabled.
|
||||
Range bound errors are always detected,
|
||||
unless runtime checks are disabled.
|
||||
.IP "set bound error"
|
||||
.br
|
||||
The detection of this error depends on the EM implementation.
|
||||
|
|
@ -313,10 +395,12 @@ The current implementations detect this error.
|
|||
The detection of this error depends on the EM implementation.
|
||||
.IP "cardinal overflow"
|
||||
.br
|
||||
This error is detected, unless runtime checks are disabled.
|
||||
This error is detected,
|
||||
unless runtime checks are disabled.
|
||||
.IP "cardinal underflow"
|
||||
.br
|
||||
This error is detected, unless runtime checks are disabled.
|
||||
This error is detected,
|
||||
unless runtime checks are disabled.
|
||||
.IP "real overflow"
|
||||
.br
|
||||
The detection of this error depends on the EM implementation.
|
||||
|
|
@ -339,9 +423,10 @@ The detection of this error depends on the EM implementation.
|
|||
.br
|
||||
This error occurs when assigning a negative value of type INTEGER to a
|
||||
variable of type CARDINAL,
|
||||
or when assigning a value of CARDINAL, that is > MAX(INTEGER), to a
|
||||
variable of type INTEGER.
|
||||
It is detected, unless runtime checking is disabled.
|
||||
or when assigning a value of CARDINAL that is > MAX(INTEGER),
|
||||
to a variable of type INTEGER.
|
||||
It is detected,
|
||||
unless runtime checking is disabled.
|
||||
.IP "stack overflow"
|
||||
.br
|
||||
The detection of this error depends on the EM implementation.
|
||||
|
|
@ -358,17 +443,22 @@ All current EM implementations detect this error.
|
|||
.IP "stack size of process too large"
|
||||
.br
|
||||
This is most likely to happen if the reserved space for a coroutine stack
|
||||
is too small. In this case, increase the size of the area given to
|
||||
\fCWNEWPROCESS\fP. It can also happen if the stack needed for the main
|
||||
process is too large and there are coroutines. In this case, the only fix is
|
||||
to reduce the stack size needed by the main process, f.i. by avoiding local
|
||||
arrays.
|
||||
is too small.
|
||||
In this case,
|
||||
increase the size of the area given to
|
||||
\f(CWNEWPROCESS\fP.
|
||||
It can also happen if the stack needed for the main
|
||||
process is too large and there are coroutines.
|
||||
In this case,
|
||||
the only fix is to reduce the stack size needed by the main process,
|
||||
f.i. by avoiding local arrays.
|
||||
.IP "too many nested traps + handlers"
|
||||
.br
|
||||
This error can only occur when the user has installed his own trap handler.
|
||||
It means that during execution of the trap handler another trap has occurred,
|
||||
and that several times.
|
||||
In some cases, this is an error because of overflow of some internal tables.
|
||||
In some cases,
|
||||
this is an error because of overflow of some internal tables.
|
||||
.IP "no RETURN from function procedure"
|
||||
.br
|
||||
This error occurs when a function procedure does not return properly
|
||||
|
|
@ -378,35 +468,53 @@ This error occurs when a function procedure does not return properly
|
|||
This error might occur when you use floating point operations on an
|
||||
implementation that does not have floating point.
|
||||
.PP
|
||||
In addition, some of the library modules may give error messages.
|
||||
In addition,
|
||||
some of the library modules may give error messages.
|
||||
The \fBTraps\fP-module has a suitable mechanism for this.
|
||||
.NH 1
|
||||
Calling the compiler
|
||||
.PP
|
||||
See [4,5,6] for a detailed explanation.
|
||||
.PP
|
||||
Ths compiler itself has no version checking mechanism. A special linker
|
||||
would be needed to do that. Therefore, a makefile generator is included [7].
|
||||
The compiler itself has no version checking mechanism.
|
||||
A special linker
|
||||
would be needed to do that.
|
||||
Therefore,
|
||||
a makefile generator is included [7].
|
||||
.NH 1
|
||||
The procedure call interface
|
||||
.PP
|
||||
Parameters are pushed on the stack in reversed order, so that the EM AB
|
||||
Parameters are pushed on the stack in reversed order,
|
||||
so that the EM AB
|
||||
(argument base) register indicates the first parameter.
|
||||
For VAR parameters, its address is passed, for value parameters its value.
|
||||
For VAR parameters,
|
||||
its address is passed,
|
||||
for value parameters its value.
|
||||
The only exception to this rule is with conformant arrays.
|
||||
For conformant arrays, the address is passed, and an array descriptor is
|
||||
passed. The descriptor is an EM array descriptor. It consists of three
|
||||
fields: the lower bound (always 0), upper bound - lower bound, and the
|
||||
size of the elements.
|
||||
For conformant arrays,
|
||||
the address is passed,
|
||||
and an array descriptor is
|
||||
passed.
|
||||
The descriptor is an EM array descriptor.
|
||||
It consists of three
|
||||
fields: the lower bound (always 0),
|
||||
upper bound - lower bound,
|
||||
and the size of the elements.
|
||||
The descriptor is pushed first.
|
||||
If the parameter is a value parameter, the called routine must make sure
|
||||
that its value is never changed, for instance by making its own copy
|
||||
of the array. The Modula-2 compiler does exactly this.
|
||||
If the parameter is a value parameter,
|
||||
the called routine must make sure
|
||||
that its value is never changed,
|
||||
for instance by making its own copy
|
||||
of the array.
|
||||
The Modula-2 compiler does exactly this.
|
||||
.PP
|
||||
When the size of the return value of a function procedure is larger than
|
||||
the maximum of \fCWSIZE(LONGREAL)\fP and twice the pointer-size, the caller
|
||||
reserves this space on the stack, above the parameters. Callee then stores
|
||||
its result there, and returns no other value.
|
||||
the maximum of \f(CWSIZE(LONGREAL)\fP and twice the pointer-size,
|
||||
the caller reserves this space on the stack,
|
||||
above the parameters.
|
||||
Callee then stores
|
||||
its result there,
|
||||
and returns no other value.
|
||||
.NH 1
|
||||
References
|
||||
.IP [1]
|
||||
|
|
|
|||
Loading…
Reference in a new issue