?? ch3-05.y
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%{#include "ch3hdr2.h"#include <string.h>#include <math.h>%}%union { double dval; struct symtab *symp;}%token <symp> NAME%token <dval> NUMBER%left '-' '+'%left '*' '/'%nonassoc UMINUS%type <dval> expression%%statement_list: statement '\n' | statement_list statement '\n' ;statement: NAME '=' expression { $1->value = $3; } | expression { printf("= %g\n", $1); } ;expression: expression '+' expression { $$ = $1 + $3; } | expression '-' expression { $$ = $1 - $3; } | expression '*' expression { $$ = $1 * $3; } | expression '/' expression { if($3 == 0.0) yyerror("divide by zero"); else $$ = $1 / $3; } | '-' expression %prec UMINUS { $$ = -$2; } | '(' expression ')' { $$ = $2; } | NUMBER | NAME { $$ = $1->value; } | NAME '(' expression ')' { if($1->funcptr) $$ = ($1->funcptr)($3); else { printf("%s not a function\n", $1->name); $$ = 0.0; } } ;%%/* look up a symbol table entry, add if not present */struct symtab *symlook(s)char *s;{ char *p; struct symtab *sp; for(sp = symtab; sp < &symtab[NSYMS]; sp++) { /* is it already here? */ if(sp->name && !strcmp(sp->name, s)) return sp; /* is it free */ if(!sp->name) { sp->name = strdup(s); return sp; } /* otherwise continue to next */ } yyerror("Too many symbols"); exit(1); /* cannot continue */} /* symlook */addfunc(name, func)char *name;double (*func)();{ struct symtab *sp = symlook(name); sp->funcptr = func;}main(){ extern double sqrt(), exp(), log(); addfunc("sqrt", sqrt); addfunc("exp", exp); addfunc("log", log); yyparse();}?? 快捷鍵說明
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