Future/bison
1
0
Fork 0
mirror of https://git.savannah.gnu.org/git/bison.git synced 2026-03-09 12:23:04 +00:00
Code Issues Packages Projects Releases Wiki Activity

examples: bistromathic: don't use Flex

Browse Source 
This example will soon use GNU readline, so its scanner should be easy
to use (concurrently) on strings, not streams.  This is not a place
where Flex shines, and anyway, these are examples of Bison, not Flex.
There's already lexcalc and reccalc that demonstrate the use of Flex.

* examples/c/bistromathic/scan.l: Remove.
* examples/c/bistromathic/parse.y (yylex): New.
Adjust dependencies.
This commit is contained in:
Akim Demaille
2020-02-29 12:04:01 +01:00
parent c4a7e7a1ab
commit 535281f0ff
5 changed files with 100 additions and 91 deletions
Download Patch File Download Diff File Expand all files Collapse all files

7
examples/c/README.md
View File

@@ -52,13 +52,12 @@ push-parser model.
## bistromathic - all the bells and whistles
This example demonstrates the best practices when using Bison.
- Its interface is pure.
- It uses a custom syntax error with location tracking, lookahead correction
and token internationalization.
- Its hand-written scanner tracks locations.
- It uses a custom syntax error with location, lookahead correction and
token internationalization.
- It supports debug traces with semantic values.
- It uses named references instead of the traditional $1, $2, etc.
It also uses Flex to generate the scanner.
<!---
Local Variables:

7
examples/c/bistromathic/README.md
View File

@@ -1,13 +1,12 @@
# bistromathic - all the bells and whistles
This example demonstrates the best practices when using Bison.
- Its interface is pure.
- It uses a custom syntax error with location tracking, lookahead correction
and token internationalization.
- Its hand-written scanner tracks locations.
- It uses a custom syntax error with location, lookahead correction and
token internationalization.
- It supports debug traces with semantic values.
- It uses named references instead of the traditional $1, $2, etc.
It also uses Flex to generate the scanner.
<!---
Local Variables:
fill-column: 76

22
examples/c/bistromathic/local.mk
View File

@@ -19,18 +19,16 @@ bistromathicdir = $(docdir)/%D%
## Bistromathics. ##
## --------------- ##
if FLEX_WORKS
check_PROGRAMS += %D%/bistromathic
TESTS += %D%/bistromathic.test
EXTRA_DIST += %D%/bistromathic.test
nodist_%C%_bistromathic_SOURCES = %D%/parse.y %D%/parse.h %D%/scan.l
%D%/calc.c: $(dependencies)
check_PROGRAMS += %D%/bistromathic
TESTS += %D%/bistromathic.test
EXTRA_DIST += %D%/bistromathic.test
nodist_%C%_bistromathic_SOURCES = %D%/parse.y %D%/parse.h
%D%/calc.c: $(dependencies)
# Don't use gnulib's system headers.
%C%_bistromathic_CPPFLAGS = -I$(top_srcdir)/%D% -I$(top_builddir)/%D%
%C%_bistromathic_LDADD = -lm
endif FLEX_WORKS
# Don't use gnulib's system headers.
%C%_bistromathic_CPPFLAGS = -I$(top_srcdir)/%D% -I$(top_builddir)/%D%
%C%_bistromathic_LDADD = -lm
dist_bistromathic_DATA = %D%/parse.y %D%/scan.l %D%/Makefile %D%/README.md
CLEANFILES += %D%/parse.[ch] %D%/scan.c %D%/parse.output
dist_bistromathic_DATA = %D%/parse.y %D%/Makefile %D%/README.md
CLEANFILES += %D%/parse.[ch] %D%/parse.output
CLEANDIRS += %D%/*.dSYM

88
examples/c/bistromathic/parse.y
View File

@@ -31,10 +31,7 @@
}
%code provides {
#define YY_DECL \
int yylex (YYSTYPE *yylval, YYLTYPE *yylloc)
YY_DECL;
int yylex (YYSTYPE *yylval, YYLTYPE *yylloc);
void yyerror (YYLTYPE *yylloc, char const *);
}
@@ -137,6 +134,10 @@ exp:
// End of grammar.
%%
/*------------.
| Functions. |
`------------*/
struct init
{
char const *name;
@@ -189,6 +190,80 @@ getsym (char const *name)
return NULL;
}
/*----------.
| Scanner. |
`----------*/
int
yylex (YYSTYPE *yylval, YYLTYPE *yylloc)
{
int c;
// Ignore white space, get first nonwhite character.
do {
// Move the first position onto the last.
yylloc->first_line = yylloc->last_line;
yylloc->first_column = yylloc->last_column;
yylloc->last_column += 1;
c = getchar ();
} while (c == ' ' || c == '\t');
switch (c)
{
case '+': return TOK_PLUS;
case '-': return TOK_MINUS;
case '*': return TOK_STAR;
case '/': return TOK_SLASH;
case '^': return TOK_CARET;
case '=': return TOK_EQUAL;
case '(': return TOK_LPAREN;
case ')': return TOK_RPAREN;
case '\n':
yylloc->last_column = 1;
yylloc->last_line += 1;
return TOK_EOL;
case EOF: return TOK_EOF;
// Any other character is a token by itself.
default:
if (c == '.' || isdigit (c))
{
ungetc (c, stdin);
int nchars = 0;
scanf ("%lf%n", &yylval->TOK_NUM, &nchars);
yylloc->last_column += nchars - 1;
return TOK_NUM;
}
else if (islower (c))
{
ungetc (c, stdin);
int nchars = 0;
char buf[100];
scanf ("%99[a-z]%n", buf, &nchars);
symrec *s = getsym (buf);
if (!s)
s = putsym (buf, TOK_VAR);
yylval->TOK_VAR = s;
yylloc->last_column += nchars - 1;
return s->type;
}
else
{
yyerror (yylloc, "error: invalid character");
return yylex (yylval, yylloc);
}
}
}
/*---------.
| Parser. |
`---------*/
int
yyreport_syntax_error (const yyparse_context_t *ctx)
{
@@ -215,6 +290,11 @@ void yyerror (YYLTYPE *loc, char const *msg)
fprintf (stderr, ": %s\n", msg);
}
/*-------.
| Main. |
`-------*/
int main (int argc, char const* argv[])
{
// Enable parse traces on option -p.

67
examples/c/bistromathic/scan.l
View File

@@ -1,67 +0,0 @@
/* Prologue (directives). -*- C -*- */
/* Disable Flex features we don't need, to avoid warnings. */
%option nodefault noinput nounput noyywrap
%{
#include <errno.h> /* errno, ERANGE */
#include <limits.h> /* INT_MIN */
#include <stdlib.h> /* strtol */
#include "parse.h"
// Each time a rule is matched, advance the end cursor/position.
#define YY_USER_ACTION \
yylloc->last_column += yyleng;
// Move the first position onto the last.
#define LOCATION_STEP() \
do { \
yylloc->first_line = yylloc->last_line; \
yylloc->first_column = yylloc->last_column; \
} while (0)
%}
%%
%{
// Each time yylex is called, move the head position to the end one.
LOCATION_STEP ();
%}
/* Rules. */
"+" return TOK_PLUS;
"-" return TOK_MINUS;
"*" return TOK_STAR;
"/" return TOK_SLASH;
"^" return TOK_CARET;
"(" return TOK_LPAREN;
")" return TOK_RPAREN;
"=" return TOK_EQUAL;
/* Scan an identifier. */
[a-z]+ {
symrec *s = getsym (yytext);
if (!s)
s = putsym (yytext, TOK_VAR);
yylval->TOK_VAR = s;
return s->type;
}
/* Scan a double precision number. */
[0-9]+(\.[0-9]*)?|(\.[0-9]+) {
sscanf (yytext, "%lf", &yylval->TOK_NUM);
return TOK_NUM;
}
"\n" yylloc->last_line++; yylloc->last_column = 1; return TOK_EOL;
/* Ignore white spaces. */
[ \t]+ LOCATION_STEP (); continue;
<<EOF>> return TOK_EOF;
. yyerror (yylloc, "error: invalid character");
%%
/* Epilogue (C code). */