fb3-1funcs.c

/* Companion source code for "flex & bison", published by O'Reilly
 * Media, ISBN 978-0-596-15597-1
 * Copyright (c) 2009, Taughannock Networks. All rights reserved.
 * See the README file for license conditions and contact info.
 * $Header: /home/johnl/flnb/code/RCS/fb3-1funcs.c,v 2.1 2009/11/08 02:53:18 johnl Exp $
 */
/*
 * helper functions for fb3-1
 */
#  include <stdio.h>
#  include <stdlib.h>
#  include <stdarg.h>
#  include "fb3-1.h"

struct ast *
newast(int nodetype, struct ast *l, struct ast *r)
{
  struct ast *a = malloc(sizeof(struct ast));
  
  if(!a) {
    yyerror("out of space");
    exit(0);
  }
  a->nodetype = nodetype;
  a->l = l;
  a->r = r;
  return a;
}

struct ast *
newnum(double d)
{
  struct numval *a = malloc(sizeof(struct numval));
  
  if(!a) {
    yyerror("out of space");
    exit(0);
  }
  a->nodetype = 'K';
  a->number = d;
  return (struct ast *)a;
}

double
eval(struct ast *a)
{
  double v;

  switch(a->nodetype) {
  case 'K': v = ((struct numval *)a)->number; break;

  case '+': v = eval(a->l) + eval(a->r); break;
  case '-': v = eval(a->l) - eval(a->r); break;
  case '*': v = eval(a->l) * eval(a->r); break;
  case '/': v = eval(a->l) / eval(a->r); break;
  case '|': v = eval(a->l); if(v < 0) v = -v; break;
  case 'M': v = -eval(a->l); break;
  default: printf("internal error: bad node %c\n", a->nodetype);
  }
  return v;
}

void
treefree(struct ast *a)
{
  switch(a->nodetype) {

    /* two subtrees */
  case '+':
  case '-':
  case '*':
  case '/':
    treefree(a->r);

    /* one subtree */
  case '|':
  case 'M':
    treefree(a->l);

    /* no subtree */
  case 'K':
    free(a);
    break;

  default: printf("internal error: free bad node %c\n", a->nodetype);
  }
}

void
yyerror(char *s, ...)
{
  va_list ap;
  va_start(ap, s);

  fprintf(stderr, "%d: error: ", yylineno);
  vfprintf(stderr, s, ap);
  fprintf(stderr, "\n");
}

int
main()
{
  printf("> "); 
  return yyparse();
}