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diff --git a/man/1/yacc b/man/1/yacc new file mode 100644 index 00000000..c3ec5868 --- /dev/null +++ b/man/1/yacc @@ -0,0 +1,349 @@ +.TH YACC 1 +.SH NAME +yacc \- yet another compiler-compiler (Limbo version) +.SH SYNOPSIS +.B yacc +[ +.I option ... +] +.I grammar +.SH DESCRIPTION +.I Yacc +converts a context-free grammar and translation code +into a set of +tables for an LR(1) parser and translator. +The grammar may be ambiguous; +specified precedence rules are used to break ambiguities. +.PP +The output from +.I yacc +is a Limbo module +.B y.tab.b +containing the parse function +.B yyparse +which must be provided with a +.B YYLEX +adt providing the parser access to a lexical analyser +routine +.BR lex() , +an error routine +.BR error() , +and any other context required. +.PP +The options are +.TP "\w'\fL-o \fIoutput\fLXX'u" +.BI -o " output +Direct output to the specified file instead of +.BR y.tab.b . +.TP +.BI -D n +Create file +.BR y.debug , +containing diagnostic messages. +To incorporate them in the parser, give an +.I n +greater than zero. +The amount of +diagnostic output from the parser is regulated by +value +.IR n : +.RS +.TP +1 +Report errors. +.TP +2 +Also report reductions. +.TP +3 +Also report the name of each token returned by +.LR yylex . +.RE +.TP +.B -v +Create file +.BR y.output , +containing a description of the parsing tables and of +conflicts arising from ambiguities in the grammar. +.TP +.B -d +Create file +.BR y.tab.m , +containing the module +declaration for the parser, along with +definitions of the constants +that associate +.IR yacc -assigned +`token codes' with user-declared `token names'. +Include it in source files other than +.B y.tab.b +to give access to the token codes and the parser module. +.TP +.BI -s " stem +Change the prefix +.L y +of the file names +.BR y.tab.b , +.BR y.tab.m , +.BR y.debug , +and +.B y.output +to +.IR stem . +.TP +.B -m +Normally +.I yacc +defines the type of the +.B y.tab.b +module within the text of the module according +to the contents of the +.B %module +directive. +Giving the +.B -m +option suppresses this behaviour, leaving the implementation +free to define the module's type from an external +.B .m +file. The module's type name is still taken from the +.B %module +directive. +.TP +.BI -n " size +Specify the initial +.I size +of the token stack created for the +parser (default: 200). +.SS Differences from C yacc +The Limbo +.I yacc +is in many respects identical to the C +.IR yacc . +The differences are summarised below: +.PP +Comments follow the Limbo convention (a +.B # +symbol gives a comment until the end of the line). +.PP +A +.B %module +directive is required, which replaces the +.B %union +directive. It is of the form: +.RS +.IP +.B %module +.I modname +.B { +.br +.I module types, functions and constants +.br +.B } +.RE +.B Modname +will be the module's implementation type; +the body of the directive, augmented with +.B con +definitions for the +.IR yacc -assigned +token codes, gives the type of the module, +unless the +.B -m +option is given, in which case no module +definition is emitted. +.PP +A type +.B YYSTYPE +must be defined, giving the type +associated with +.I yacc +tokens. If +the angle bracket construction is used after +any of the +.BR %token , +.BR %left , +.BR %right , +.BR %nonassoc +or +.B %type +directives in order to associate a type with a token or production, +the word inside the angle brackets +refers to a member of +an instance of +.BR YYSTYPE , +which should be an adt. +.PP +An adt +.B YYLEX +must be defined, providing context to the parser. +The definition must consist of at least the following: +.EX + YYLEX: adt { + lval: YYSTYPE; + lex: fn(l: self ref YYLEX): int; + error: fn(l: self ref YYLEX, msg: string); + } +.EE +.B Lex +should invoke a lexical analyser to return the +next token for +.I yacc +to analyse. The value of the token should +be left in +.BR lval . +.B Error +will be called when a parse error occurs. +.B Msg +is a string describing the error. +.PP +.B Yyparse +takes one argument, a reference to the +.B YYLEX +adt that will be used to provide it with tokens. +.PP +The parser is fully re-entrant; +.I i.e. +it does not +hold any parse state in any global variables +within the module. +.SH EXAMPLE +The following is a small but complete example of the +use of Limbo +.I yacc +to build a simple calculator. +.EX +%{ + include "sys.m"; + sys: Sys; + + include "bufio.m"; + bufio: Bufio; + Iobuf: import bufio; + + include "draw.m"; + + YYSTYPE: adt { v: real; }; + YYLEX: adt { + lval: YYSTYPE; + lex: fn(l: self ref YYLEX): int; + error: fn(l: self ref YYLEX, msg: string); + }; +%} + +%module Calc{ + init: fn(ctxt: ref Draw->Context, args: list of string); +} + +%left '+' '-' +%left '*' '/' + +%type <v> exp uexp term +%token <v> REAL + +%% +top : + | top '\en' + | top exp '\en' + { + sys->print("%g\en", $2); + } + | top error '\en' + ; + +exp : uexp + | exp '*' exp { $$ = $1 * $3; } + | exp '/' exp { $$ = $1 / $3; } + | exp '+' exp { $$ = $1 + $3; } + | exp '-' exp { $$ = $1 - $3; } + ; + +uexp : term + | '+' uexp { $$ = $2; } + | '-' uexp { $$ = -$2; } + ; + +term : REAL + | '(' exp ')' + { + $$ = $2; + } + ; + +%% + +in: ref Iobuf; +stderr: ref Sys->FD; + +init(nil: ref Draw->Context, nil: list of string) +{ + sys = load Sys Sys->PATH; + bufio = load Bufio Bufio->PATH; + in = bufio->fopen(sys->fildes(0), Bufio->OREAD); + stderr = sys->fildes(2); + lex := ref YYLEX; + yyparse(lex); +} + +YYLEX.error(nil: self ref YYLEX, err: string) +{ + sys->fprint(stderr, "%s\en", err); +} + +YYLEX.lex(lex: self ref YYLEX): int +{ + for(;;){ + c := in.getc(); + case c{ + ' ' or '\et' => + ; + '-' or '+' or '*' or '/' or '\en' or '(' or ')' => + return c; + '0' to '9' or '.' => + s := ""; + i := 0; + s[i++] = c; + while((c = in.getc()) >= '0' && c <= '9' || + c == '.' || + c == 'e' || c == 'E') + s[i++] = c; + in.ungetc(); + lex.lval.v = real s; + return REAL; + * => + return -1; + } + } +} +.EE +.SH FILES +.TF /lib/yaccpar +.TP +.B y.output +.TP +.B y.tab.b +.TP +.B y.tab.m +.TP +.B y.debug +.TP +.B /lib/yaccpar +parser prototype +.SH SOURCE +.B /appl/cmd/yacc.b +.SH "SEE ALSO" +S. C. Johnson and R. Sethi, +``Yacc: A parser generator'', +.I +Unix Research System Programmer's Manual, +Tenth Edition, Volume 2 +.br +B. W. Kernighan and Rob Pike, +.I +The UNIX Programming Environment, +Prentice Hall, 1984 +.SH BUGS +The parser may not have full information when it writes to +.B y.debug +so that the names of the tokens returned by +.L yylex +may be missing. |