crisp/eval.c

//
// Created by red on 05/12/19.
//

#include "eval.h"

// create number type cval
cval cval_num(long x) {
  cval v;
  v.type = CVAL_NUM;
  v.num = x;
  return v;
}

// create error type cval
cval cval_err(int x){
  cval v;
  v.type = CVAL_ERR;
  v.err = x;
  return v;
}


void cval_print(cval v) {
  switch (v.type) {
  case CVAL_NUM: printf("%li", v.num); break;
  case CVAL_ERR: {
    switch (v.err) {
    case CERR_DIV_ZERO: printf("Error: Division by zero"); break;
    case CERR_BAD_OP: printf("Error: Invalid operator"); break;
    case CERR_BAD_NUM: printf("Error: Invalid number"); break;
    default: break;
    }
  }
  default: break;
  }
}

void cval_println(cval v) {
  cval_print(v);
  putchar('\n');
}

cval eval_op(cval x, char* op, cval y) {
  if (x.type == CVAL_ERR) {return x;}
  if (y.type == CVAL_ERR) {return y;}
  switch (*op) {
  case '+': return cval_num(x.num + y.num);
  case '-': return cval_num(x.num - y.num);
  case '*': return cval_num(x.num * y.num);
  //return error
  case '/': return y.num == 0 ? cval_err(CERR_DIV_ZERO) : cval_num(x.num / y.num);
  default: return cval_err(CERR_BAD_OP);
  }
}

cval eval(mpc_ast_t* t) {

  if (strstr(t->tag, "number")) {
    errno = 0;
    long x = strtol(t->contents, NULL, 10);
    return errno != ERANGE ? cval_num(x) : cval_err(CERR_BAD_NUM);
  }

  // the operator is always the second child
  char* op = t->children[1]->contents;
  cval x = eval(t->children[2]);

  // iterate over the remaining children and combine
  int i = 3;
  while (strstr(t->children[i]->tag, "expr")) {
    x = eval_op(x, op, eval(t->children[i]));
    i++;
  }

  return x;
}