168 lines
3.2 KiB
Plaintext
168 lines
3.2 KiB
Plaintext
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.TH YACC 1
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.SH NAME
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yacc \- yet another compiler-compiler
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.SH SYNOPSIS
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.B yacc
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[
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.I option ...
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]
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.I grammar
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.SH DESCRIPTION
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.I Yacc
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converts a context-free grammar and translation code
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into a set of
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tables for an LR(1) parser and translator.
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The grammar may be ambiguous;
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specified precedence rules are used to break ambiguities.
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.PP
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The output file,
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.BR y.tab.c ,
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must be compiled by the C compiler
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to produce a program
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.LR yyparse .
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This program must be loaded with a lexical analyzer function,
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.B yylex(void)
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(often generated by
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.IR lex (1)),
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with a
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.B main(int argc, char *argv[])
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program, and with an error handling routine,
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.BR yyerror(char*) .
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.PP
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The options are
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.TP "\w'\fL-o \fIoutput\fLXX'u"
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.BI -o " output
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Direct output to the specified file instead of
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.BR y.tab.c .
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.TP
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.BI -D n
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Create file
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.BR y.debug ,
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containing diagnostic messages.
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To incorporate them in the parser, compile it with preprocessor symbol
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.B yydebug
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defined.
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The amount of
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diagnostic output from the parser is regulated by
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value
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.IR n .
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The value 0 reports errors; 1 reports reductions;
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higher values (up to 4) include more information about
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state transitions.
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.TP
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.B -v
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Create file
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.BR y.output ,
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containing a description of the parsing tables and of
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conflicts arising from ambiguities in the grammar.
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.TP
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.B -d
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Create file
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.BR y.tab.h ,
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containing
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.B #define
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statements that associate
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.IR yacc -assigned
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`token codes' with user-declared `token names'.
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Include it in source files other than
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.B y.tab.c
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to give access to the token codes.
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.TP
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.BI -s " stem
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Change the prefix
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.L y
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of the file names
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.BR y.tab.c ,
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.BR y.tab.h ,
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.BR y.debug ,
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and
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.B y.output
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to
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.IR stem .
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.TP
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.B -S
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Write a parser that uses
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Stdio
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instead of the
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.B print
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routines in libc.
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.PP
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The specification of
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.I yacc
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itself is essentially the same as the UNIX version
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described in the references mentioned below.
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Besides the
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.B -D
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option, the main relevant differences are:
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.IP
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The interface to the C environment is by default through
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.B <libc.h>
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rather than
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.BR <stdio.h> ;
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the
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.B -S
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option reverses this.
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.IP
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The parser accepts
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.SM UTF
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input text (see
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.IR utf (6)),
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which has a couple of effects.
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First, the return value of
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.B yylex()
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no longer fits in a
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.BR short ;
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second, the starting value for non-terminals is now 0xE000 rather than 257.
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.IP
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The generated parser can be recursive: actions can call
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.IR yyparse ,
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for example to implement a sort of
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.B #include
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statement in an interpreter.
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.IP
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Finally, some undocumented inner workings of the parser have been
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changed, which may affect programs that know too much about its structure.
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.SH FILES
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.TF /sys/lib/yaccpars
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.TP
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.B y.output
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.TP
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.B y.tab.c
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.TP
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.B y.tab.h
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.TP
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.B y.debug
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.TP
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.B y.tmp.*
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temporary file
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.TP
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.B y.acts.*
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temporary file
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.TP
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.B /sys/lib/yaccpar
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parser prototype
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.TP
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.B /sys/lib/yaccpars
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parser prototype using stdio
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.SH SOURCE
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.B /sys/src/cmd/yacc.c
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.SH "SEE ALSO"
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.IR lex (1)
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.br
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S. C. Johnson and R. Sethi,
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``Yacc: A parser generator'',
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.I
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Unix Research System Programmer's Manual,
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Tenth Edition, Volume 2
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.br
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B. W. Kernighan and Rob Pike,
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.I
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The UNIX Programming Environment,
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Prentice Hall, 1984
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.SH BUGS
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The parser may not have full information when it writes to
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.B y.debug
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so that the names of the tokens returned by
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.L yylex
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may be missing.
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