fb3-1.c

#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 memory");
    exit(0);
  }
  a->nodetype = nodetype;
  a->l = l;
  a->r = r;
  return a;
}

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

double
eval(struct ast *a)
{
  double v; // calculated value of this subtree
  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();
}