259 lines
7.1 KiB
Groff
259 lines
7.1 KiB
Groff
.\" $Id: yacc.1,v 1.20 2014/01/01 17:40:13 tom Exp $
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.\" .TH YACC 1 "July\ 15,\ 1990"
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.TH YACC 1 "January 1, 2014" "Berkeley Yacc" "User Commands"
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.SH NAME
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Yacc \- an LALR(1) parser generator
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.SH SYNOPSIS
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.B yacc [ -dgilrtv ] [ \-b
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.I file_prefix
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.B ] [ \-p
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.I symbol_prefix
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.B ]
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.I filename
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.SH DESCRIPTION
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.B Yacc
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reads the grammar specification in the file
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.I filename
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and generates an LALR(1) parser for it.
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The parsers consist of a set of LALR(1) parsing tables and a driver routine
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written in the C programming language.
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.B Yacc
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normally writes the parse tables and the driver routine to the file
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.IR y.tab.c.
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.PP
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The following options are available:
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.TP 5
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\fB\-b \fP\fIfile_prefix\fR
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The
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.B \-b
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option changes the prefix prepended to the output file names to
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the string denoted by
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.IR file_prefix.
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The default prefix is the character
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.IR y.
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.TP
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.B \-d
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The \fB-d\fR option causes the header file
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.BR y.tab.h
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to be written.
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It contains #define's for the token identifiers.
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.TP
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.B \-g
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The
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.B \-g
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option causes a graphical description of the generated LALR(1) parser to
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be written to the file
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.BR y.dot
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in graphviz format, ready to be processed by dot(1).
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.TP
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.B \-i
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The \fB-i\fR option causes a supplementary header file
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.BR y.tab.i
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to be written.
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It contains extern declarations
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and supplementary #define's as needed to map the conventional \fIyacc\fP
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\fByy\fP-prefixed names to whatever the \fB-p\fP option may specify.
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The code file, e.g., \fBy.tab.c\fP is modified to #include this file
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as well as the \fBy.tab.h\fP file, enforcing consistent usage of the
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symbols defined in those files.
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.IP
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The supplementary header file makes it simpler to separate compilation
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of lex- and yacc-files.
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.TP
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.B \-l
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If the
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.B \-l
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option is not specified,
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.B yacc
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will insert \fI#line\fP directives in the generated code.
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The \fI#line\fP directives let the C compiler relate errors in the
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generated code to the user's original code.
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If the \fB-l\fR option is specified,
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.B yacc
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will not insert the \fI#line\fP directives.
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\&\fI#line\fP directives specified by the user will be retained.
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.TP
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\fB\-o \fP\fIoutput_file\fR
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specify the filename for the parser file.
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If this option is not given, the output filename is
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the file prefix concatenated with the file suffix, e.g., \fBy.tab.c\fP.
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This overrides the \fB-p\fP option.
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.TP
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\fB\-p \fP\fIsymbol_prefix\fR
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The
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.B \-p
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option changes the prefix prepended to yacc-generated symbols to
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the string denoted by
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.IR symbol_prefix.
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The default prefix is the string
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.BR yy.
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.TP
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.B \-P
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create a reentrant parser, e.g., \*(``%pure-parser\*(''.
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.TP
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.B \-r
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The
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.B \-r
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option causes
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.B yacc
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to produce separate files for code and tables.
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The code file is named
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.IR y.code.c,
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and the tables file is named
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.IR y.tab.c.
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The prefix \*(``\fIy.\fP\*('' can be overridden using the \fB\-b\fP option.
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.TP
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.B \-s
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suppress \*(``\fB#define\fP\*('' statements generated for string literals in
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a \*(``\fB%token\fP\*('' statement,
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to more closely match original \fByacc\fP behavior.
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.IP
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Normally when \fByacc\fP sees a line such as
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.ES
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%token OP_ADD "ADD"
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.XE
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.IP
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it notices that the quoted \*(``ADD\*('' is a valid C identifier,
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and generates a #define not only for OP_ADD,
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but for ADD as well,
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e.g.,
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.ES
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#define OP_ADD 257
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.br
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#define ADD 258
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.XE
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.IP
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The original \fByacc\fP does not generate the second \*(``\fB#define\fP\*(''.
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The \fB\-s\fP option suppresses this \*(``\fB#define\fP\*(''.
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.IP
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POSIX (IEEE 1003.1 2004) documents only names and numbers
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for \*(``\fB%token\fP\*('',
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though original \fByacc\fP and bison also accept string literals.
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.TP
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.B \-t
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The
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.B \-t
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option changes the preprocessor directives generated by
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.B yacc
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so that debugging statements will be incorporated in the compiled code.
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.TP
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.B \-v
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The
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.B \-v
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option causes a human-readable description of the generated parser to
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be written to the file
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.IR y.output.
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.TP
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.B \-V
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print the version number to the standard output.
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.TP
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.B \-y
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\fByacc\fP ignores this option,
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which bison supports for ostensible POSIX compatibility.
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.SH EXTENSIONS
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.B yacc
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provides some extensions for
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compatibility with bison and other implementations of yacc:
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.TP
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\fB %expect\fP \fInumber\fP
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tell \fByacc\fP the expected number of shift/reduce conflicts.
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That makes it only report the number if it differs.
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.TP
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\fB %expect-rr\fP \fInumber\fP
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tell \fByacc\fP the expected number of reduce/reduce conflicts.
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That makes it only report the number if it differs.
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This is (unlike bison) allowable in LALR parsers.
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.TP
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\fB %lex-param\fP { \fIargument-declaration\fP }
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By default, the lexer accepts no parameters, e.g., \fByylex()\fP.
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Use this directive to add parameter declarations for your customized lexer.
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.TP
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\fB %parse-param\fP { \fIargument-declaration\fP }
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By default, the parser accepts no parameters, e.g., \fByyparse()\fP.
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Use this directive to add parameter declarations for your customized parser.
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.TP
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\fB %pure-parser\fP
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Most variables (other than \fByydebug\fP and \fByynerrs\fP) are
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allocated on the stack within \fByyparse\fP, making the parser reasonably
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reentrant.
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.TP
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\fB %token-table\fP
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Make the parser's names for tokens available in the \fByytname\fP array.
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However,
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.B yacc
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does not predefine \*(``$end\*('', \*(``$error\*(''
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or \*(``$undefined\*('' in this array.
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.SH PORTABILITY
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According to Robert Corbett,
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.ES
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Berkeley Yacc is an LALR(1) parser generator. Berkeley Yacc has been made
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as compatible as possible with AT&T Yacc. Berkeley Yacc can accept any input
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specification that conforms to the AT&T Yacc documentation. Specifications
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that take advantage of undocumented features of AT&T Yacc will probably be
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rejected.
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.XE
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.PP
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The rationale in
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.ES
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http://pubs.opengroup.org/onlinepubs/9699919799/utilities/yacc.html
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.XE
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.PP
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documents some features of AT&T yacc which are no longer required for POSIX
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compliance.
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.PP
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That said, you may be interested in reusing grammary files with some
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other implementation which is not strictly compatible with AT&T yacc.
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For instance, there is bison.
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Here are a few differences:
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.bP
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\fBYacc\fP accepts an equals mark preceding the left curly brace
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of an action (as in the original grammar file \fBftp.y\fP):
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.ES
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| STAT CRLF
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= {
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statcmd();
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}
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.XE
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.bP
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\fBYacc\fP and bison emit code in different order, and in particular bison
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makes forward reference to common functions such as yylex, yyparse and
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yyerror without providing prototypes.
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.bP
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Bison's support for \*(``%expect\*('' is broken in more than one release.
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For best results using bison, delete that directive.
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.bP
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Bison has no equivalent for some of \fByacc\fP's commmand-line options,
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relying on directives embedded in the grammar file.
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.bP
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Bison's \*(``\fB\-y\fP\*('' option does not affect bison's lack of support for
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features of AT&T yacc which were deemed obsolescent.
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.
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.SH DIAGNOSTICS
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If there are rules that are never reduced, the number of such rules is
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reported on standard error.
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If there are any LALR(1) conflicts, the number of conflicts is reported
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on standard error.
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