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/* Parser for reccalc. -*- C -*-
Copyright (C) 2019-2022 Free Software Foundation, Inc.
This file is part of Bison, the GNU Compiler Compiler.
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <https://www.gnu.org/licenses/>. */
// Prologue (directives).
%expect 0
// Emitted in the header file, before the definition of YYSTYPE.
%code requires
{
#ifndef YY_TYPEDEF_YY_SCANNER_T
# define YY_TYPEDEF_YY_SCANNER_T
typedef void* yyscan_t;
#endif
typedef struct
{
// Whether to print the intermediate results.
int verbose;
// Value of the last computation.
int value;
// Number of errors.
int nerrs;
} result;
}
// Emitted in the header file, after the definition of YYSTYPE.
%code provides
{
// Tell Flex the expected prototype of yylex.
// The scanner argument must be named yyscanner.
#define YY_DECL \
yytoken_kind_t yylex (YYSTYPE* yylval, yyscan_t yyscanner, result *res)
YY_DECL;
void yyerror (yyscan_t scanner, result *res, const char *msg, ...);
}
// Emitted on top of the implementation file.
%code top
{
#include <stdarg.h> // va_list.
#include <stdio.h> // printf.
#include <stdlib.h> // getenv.
}
%code
{
result parse_string (const char* cp);
result parse (void);
}
// Include the header in the implementation rather than duplicating it.
%define api.header.include {"parse.h"}
// Don't share global variables between the scanner and the parser.
%define api.pure full
// To avoid name clashes (e.g., with C's EOF) prefix token definitions
// with TOK_ (e.g., TOK_EOF).
%define api.token.prefix {TOK_}
// Generate YYSTYPE from the types assigned to symbols.
%define api.value.type union
// Error messages with "unexpected XXX, expected XXX...".
%define parse.error detailed
// Enable run-time traces (yydebug).
%define parse.trace
// Generate the parser description file (parse.output).
%verbose
// Scanner and error count are exchanged between main, yyparse and yylex.
%param {yyscan_t scanner}{result *res}
%token
PLUS "+"
MINUS "-"
STAR "*"
SLASH "/"
EOL "end-of-line"
EOF 0 "end-of-file"
;
%token <int> NUM "number"
%type <int> exp
%printer { fprintf (yyo, "%d", $$); } <int>
%token <char*> STR "string"
%printer { fprintf (yyo, "\"%s\"", $$); } <char*>
%destructor { free ($$); } <char*>
// Precedence (from lowest to highest) and associativity.
%left "+" "-"
%left "*" "/"
%precedence UNARY
%%
// Rules.
input:
line
| input line
;
line:
exp eol
{
res->value = $exp;
if (res->verbose)
printf ("%d\n", $exp);
}
| error eol
{
yyerrok;
}
;
eol:
EOF
| EOL
;
exp:
NUM { $$ = $1; }
| exp "+" exp { $$ = $1 + $3; }
| exp "-" exp { $$ = $1 - $3; }
| exp "*" exp { $$ = $1 * $3; }
| exp "/" exp
{
if ($3 == 0)
{
yyerror (scanner, res, "invalid division by zero");
YYERROR;
}
else
$$ = $1 / $3;
}
| "+" exp %prec UNARY { $$ = + $2; }
| "-" exp %prec UNARY { $$ = - $2; }
| STR
{
result r = parse_string ($1);
free ($1);
if (r.nerrs)
{
res->nerrs += r.nerrs;
YYERROR;
}
else
$$ = r.value;
}
;
%%
// Epilogue (C code).
#include "scan.h"
result
parse (void)
{
yyscan_t scanner;
yylex_init (&scanner);
result res = {1, 0, 0};
yyparse (scanner, &res);
yylex_destroy (scanner);
return res;
}
result
parse_string (const char *str)
{
yyscan_t scanner;
yylex_init (&scanner);
YY_BUFFER_STATE buf = yy_scan_string (str ? str : "", scanner);
result res = {0, 0, 0};
yyparse (scanner, &res);
yy_delete_buffer (buf, scanner);
yylex_destroy (scanner);
return res;
}
void
yyerror (yyscan_t scanner, result *res,
const char *msg, ...)
{
(void) scanner;
va_list args;
va_start (args, msg);
vfprintf (stderr, msg, args);
va_end (args);
fputc ('\n', stderr);
res->nerrs += 1;
}
int
main (void)
{
// Possibly enable parser runtime debugging.
yydebug = !!getenv ("YYDEBUG");
result res = parse ();
// Exit on failure if there were errors.
return !!res.nerrs;
}
|
