evaluation.c

#include "mpc.h"

#include <editline/readline.h>

long eval_op(long x, char* op, long y) {
  if (strcmp(op, "+") == 0) { return x + y;}
  if (strcmp(op, "-") == 0) { return x - y;}
  if (strcmp(op, "*") == 0) { return x * y;}
  if (strcmp(op, "/") == 0) { return x / y;}
  return 0;
}

long eval(mpc_ast_t* t) {
  if (strstr(t->tag, "number")) {
    return atoi(t->contents);
  }

  char* op = t->children[1]->contents;
  long x = eval(t->children[2]);

  int i = 3;
  while(strstr(t->children[i]->tag, "expr")) {
    x = eval_op(x, op, eval(t->children[i]));
    i++;
  }

  return x;
}

int main(int argc, char** argv) {
  mpc_parser_t* Number = mpc_new("number");
  mpc_parser_t* Operator = mpc_new("operator");
  mpc_parser_t* Expr = mpc_new("expr");
  mpc_parser_t* Lispy = mpc_new("lispy");

  mpca_lang(MPCA_LANG_DEFAULT,
            "                                                     \
      number   : /-?[0-9]+/ ;                             \
      operator : '+' | '-' | '*' | '/' ;                  \
      expr     : <number> | '(' <operator> <expr>+ ')' ;  \
      lispy    : /^/ <operator> <expr>+ /$/ ;             \
    ",
            Number, Operator, Expr, Lispy);

  puts("Lispy 0.0.0.0.0.0.2");
  puts("Press C-c to exit.");

  while(1) {
    char *input = readline("lispy> ");
    add_history(input);

    mpc_result_t r;
    if(mpc_parse("<stdin>", input, Lispy, &r)) {
      long result = eval(r.output);
      printf("%li\n", result);
      mpc_ast_delete(r.output);
    } else {
      mpc_err_print(r.error);
      mpc_err_delete(r.error);
    }

    free(input);
  }

  mpc_cleanup(4, Number, Operator, Expr, Lispy);

  return 0;
}