Re: Flex-Bison track sample

[Hans Aberg]

At 17:23 +0300 0-12-02, Vladimir Rykov wrote:
>So - how [might] all the commands for Flex - Bison - GCC (I mean their
>command >line options) to start them and get together the results will
>look for a simple
>case?

A simple example for use with C is given in the book by Aho, Sethi & Ullman
"Compilers...". I will give my version of it (below).

-- I cannot be positively sure you get a working version as it stands, but
it should be possible to make it working.

There are two styles of using Flex & Bison together, one (traditional)
where the Flex .c output file is included in the Bison .c output file, and
one (better  C style), where they share a common header. The version below
is the latter form, even though it has a "#if .." directive which could be
used if one wants to use the traditional style.

I also have a simple examples that I made for Flex and Bison output
compiled using C++ (Both without and with Bison source code tweaks). --
Perhaps another post, if somebody is interested.

-- File LexCalc.h -----------------------------------------------------


#ifndef LexCalc_h
#define LexCalc_h


#include <math.h>


typedef union calc_type {
        double value;
        char* name;
        int length;
} calc_type;

#define YYSTYPE calc_type

#endif

-- File LexCalc.l, Compile using flex -Pcalc_ -a ---------------------------


#include "LexCalc.h"

#define yylval calc_lval

#include "LexCalc.tab.h"



%}

%option noyywrap

digit           [0-9]
number          {digit}+\.?|{digit}*\.{digit}+
identifier  [a-zA-Z]+

%%

[ ]                      { /* Skip blanks. */ }
{number}         { sscanf(yytext, "%lf", &yylval.value);
                           return NUMBER; }
"exit"           { return EXIT; }
{identifier} { yylval.name = yytext; yylval.length = yyleng; return
IDENTIFIER; }
\n|.             { return yytext[0]; }

%%

-- File LexCalc.y, Compile using bison --defines --name-prefix=calc_ --------


%{
        /* From Aho, Seti, Ullman, fig. 4.59, p. 266. */

#include "LexCalc.h"

%}

%token NUMBER
%token IDENTIFIER
%token EXIT

%left '+' '-'
%left '*' '/'
%right '^'
%right IDENTIFIER
%right UMINUS

%%
lines:  lines expr '\n'         { printf("%.12g\n", $2.value) }
        |       lines '\n'
        |       lines EXIT '\n'         { return EXIT_SUCCESS; }
        |       /* empty */
        |       error '\n'              { printf("Please re-enter last
line: ");
                                  yyerrok; }
        ;

expr:   expr '+' expr   { $$.value = $1.value + $3.value }
        |       expr '-' expr   { $$.value = $1.value - $3.value }
        |       expr '*' expr   { $$.value = $1.value * $3.value }
        |       expr '/' expr   { $$.value = $1.value / $3.value }
        |       expr '^' expr   { $$.value = pow($1.value, $3.value) }
        |       '(' expr ')'    { $$.value = $2.value }
        |       '-' expr  %prec UMINUS { $$.value = -$2.value }
        |       IDENTIFIER expr { $$.value = sqrt($2.value) }
        |       NUMBER
        ;

%%
#include <ctype.h>
#include <stdio.h>

#if 0
#include "lex.calc_.c"
#endif

#if __MWERKS__ && macintosh
#include <SIOUX.h>
#endif

int main() {
#if __MWERKS__ && macintosh
        SIOUXSettings.asktosaveonclose = 0;
        SIOUXSettings.autocloseonquit = 1;
#endif
        return yyparse();
}

int yyerror(char* errstr) {
        printf("Error: %s\n", errstr);
        return EXIT_FAILURE;
}

-- File MoreAdvancedCalc.y, Compile using bison --defines --name-prefix=calc_


%{
        /* From Aho, Seti, Ullman, fig. 4.56, p. 259. */

#include <math.h>

#define YYSTYPE double
%}

%token NUMBER
%left '+' '-'
%left '*' '/'
%right '^'
%right UMINUS

%%
lines:  lines expr '\n'         { printf("%.12g\n", $2) }
        |       lines '\n'
        |       /* empty */
        ;

expr:   expr '+' expr   { $$ = $1 + $3 }
        |       expr '-' expr   { $$ = $1 - $3 }
        |       expr '*' expr   { $$ = $1 * $3 }
        |       expr '/' expr   { $$ = $1 / $3 }
        |       expr '^' expr   { $$ = pow($1, $3) }
        |       '(' expr ')'    { $$ = $2 }
        |       '-' expr  %prec UMINUS { $$ = -$2 }
        |       NUMBER
        ;

%%
#include <ctype.h>
#include <stdio.h>

yylex() {
        int c;
        while ((c = getc(stdin)) == ' ')
                ;
        if ((c == '.') || isdigit(c)) {
                ungetc(c, stdin);
                scanf("%lf", &yylval);
                return NUMBER;
        }
        return c;
}

#if __MWERKS__ && macintosh
#include <SIOUX.h>
#endif

int main() {
#if __MWERKS__ && macintosh
        SIOUXSettings.asktosaveonclose = 0;
        SIOUXSettings.autocloseonquit = 0;
#endif
        return yyparse();
}

int yyerror(char* errstr) {
        printf("Error: %s\n", errstr);
        printf("(Exit)\n");
        exit(EXIT_FAILURE);
        return EXIT_SUCCESS;
}

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