UNIX — универсальная среда программирования - Керниган Брайан Уилсон
char *name;
short type; /* VAR, BLTIN, UNDEF */
union {
double val; /* if VAR */
double (*ptr)(); /* if BLTIN */
} u;
struct Symbol *next; /* to link to another */
} Symbol;
Symbol *install(), *lookup();
3.4.2 hoc.y
%{
#include "hoc.h"
extern double Pow();
%}
%union {
double val; /* actual value */
Symbol *sym; /* symbol table pointer */
}
%token <val> NUMBER
%token <sym> VAR BLTIN UNDEF
%type <val> expr asgn
%right '='
%left '+' '-'
%left '*' '/'
%left UNARYMINUS
%right '^' /* exponentiation */
%%
list: /* nothing */
| list 'n'
| list asgn 'n'
| list expr 'n' { printf("t%.8gn", $2); }
| list error 'n' { yyerrok; }
;
asgn: VAR '=' expr { $$=$1->u.val=$3; $1->type = VAR; }
;
expr: NUMBER
| VAR {
if ($1->type == UNDEF)
execerror("undefined variable", $1->name);
$$ = $1->u.val;
}
| asgn
| BLTIN '(' expr ')' { $$ = (*($1->u.ptr))($3); }
| expr '+' expr { $$ = $1 + $3; }
| expr '+' expr { $$ = $1 - $3; }
| expr '*' expr { $$ = $1 * $3; }
| expr '/' expr {
if ($3 == 0.0)
execerror("division by zero", "");
$$ = $1 / $3;
}
| expr '^' expr { $$ = Pow($1, $3); }
| '(' expr ')' { $$ = $2; }
| '-' expr %prec UNARYMINUS { $$ = -$2; }
;
%%
/* end of grammar */
#include <stdio.h>
#include <ctype.h>
char *progname;
int lineno = 1;
#include <setjmp.h>
jmp_buf begin;
main(argc, argv) /* hoc3 */
char *argv[];
{
progname = argv[0];
init();
setjmp(begin);
yyparse();
}
yyerror(s)
char *s;
{
warning(s, (char *)0);
}
execerror(s, t)
char *s, *t;
{
warning(s, t);
longjmp(begin, 0);
}
warning(s, t)
char *s, *t;
{
fprintf (stderr, "%s: %s", progname, s);
if (t && *t)
fprintf(stderr, " %s", t);
fprintf(stderr, " near line %dn", lineno);
}
3.4.3 init.c
#include "hoc.h"
#include "y.tab.h"
#include <math.h>
extern double Log(), Log10(), Exp(), Sqrt(), integer();
static struct { /* Constants */
char *name;
double eval;
} consts [] = {
"PI", 3.14159265358979323846,
"E", 2.71828182845904523536,
"GAMMA", 0.57721566490153286060, /* Euler */
"DEG", 57.29577951308232087680, /* deg/radian */
"PHI", 1.61803398874989484820, /* golden ratio */
0, 0
};
static struct { /* Built-ins */
char *name;
