s_expressions.c

#include "mpc.h"

#include <editline/readline.h>

enum { LVAL_ERR, LVAL_NUM, LVAL_SYM, LVAL_SEXPR};

typedef struct lval {
  int type;
  long num;
  /* Error and Symbol types have some string data */
  char* err;
  char* sym;
  /* Count and Pointer to a list of "lval*"; */
  int count;
  struct lval** cell;
} lval;

lval* lval_num(long x) {
  lval* v = malloc(sizeof(lval));
  v->type = LVAL_NUM;
  v->num = x;
  return v;
}

lval* lval_err(char* m) {
  lval* v = malloc(sizeof(lval));
  v->type = LVAL_ERR;
  v->err = malloc(strlen(m) + 1);
  strcpy(v->err, m);
  return v;
}

lval* lval_sym(char* s) {
  lval* v = malloc(sizeof(lval));
  v->type = LVAL_SYM;
  v->sym = malloc(strlen(s) + 1);
  strcpy(v->sym, s);
  return v;
}

lval* lval_sexpr(void) {
  lval* v = malloc(sizeof(lval));
  v->type = LVAL_SEXPR;
  v->count = 0;
  v->cell = NULL;
  return v;
}

void lval_del(lval* v) {
  switch (v->type) {
  case LVAL_NUM:
    break;
  case LVAL_ERR:
    free(v->err);
    break;
  case LVAL_SYM:
    free(v->sym);
    break;
  case LVAL_SEXPR:
    for (int i = 0; i < v->count; i++) {
      lval_del(v->cell[i]);
    }
    free(v->cell);
  }
  free(v);
}

lval* lval_add(lval* v, lval* x) {
  v->count++;
  v->cell = realloc(v->cell, sizeof(lval*) * v->count);
  v->cell[v->count - 1] = x;
  return v;
}

lval* lval_pop(lval* v, int i) {
  lval* x = v->cell[i];
  memmove(&v->cell[i], &v->cell[i + 1], sizeof(lval*) * (v->count - i - 1));
  v->count--;
  v->cell = realloc(v->cell, sizeof(lval*) * v->count);
  return x;
}

lval* lval_take(lval* v, int i) {
  lval* x = lval_pop(v, i);
  lval_del(v);
  return x;
}

void lval_print(lval* v);

void lval_expr_print(lval* v, char open, char close) {
  putchar(open);
  for (int i = 0; i < v->count; i++) {
    lval_print(v->cell[i]);

    /* No trailing space in the last element */
    if (i != (v->count - 1)) {
      putchar(' ');
    }
  }
  putchar(close);
}

void lval_print(lval* v) {
  switch (v->type) {
    case LVAL_NUM:
      printf("%li", v->num);
      break;
    case LVAL_ERR:
      printf("Error: %s", v->err);
      break;
    case LVAL_SYM:
      printf("%s", v->sym);
      break;
    case LVAL_SEXPR:
      lval_expr_print(v, '(', ')');
      break;
  }
}

void lval_println(lval* v) {
  lval_print(v);
  putchar('\n');
}

lval* builtin_op(lval* a, char* op) {
  for (int i = 0; i < a->count; i++) {
    if (a->cell[i]->type != LVAL_NUM) {
      lval_del(a);
      return lval_err("Cannot operate on non-number");
    }
  }

  lval* x = lval_pop(a, 0);

  /* In case of no arguments, just do unary negation */
  if ((strcmp(op, "-") == 0) && a->count == 0) {
    x->num = -x->num;
  }

  while (a->count > 0) {
    lval* y = lval_pop(a, 0);

    if (strcmp(op, "+") == 0) {
      x->num += y->num;
    }
    if (strcmp(op, "-") == 0) {
      x->num -= y->num;
    }
    if (strcmp(op, "*") == 0) {
      x->num *= y->num;
    }
    if (strcmp(op, "/") == 0) {
      if (y->num == 0) {
        lval_del(x);
        lval_del(y);
        x = lval_err("Division by zero!");
        break;
      }
      x->num /= y->num;
    }
    lval_del(y);
  }
  lval_del(a);
  return x;
}

lval* lval_eval(lval* v);

lval* lval_eval_sexpr(lval* v) {
  for (int i = 0; i < v->count; i++) {
    v->cell[i] = lval_eval(v->cell[i]);
  }

  for (int i = 0; i < v->count; i++) {
    if (v->cell[i]->type == LVAL_ERR) {
      return lval_take(v, i);
    }
  }

  if (v->count == 0) {
    return v;
  }

  if (v->count == 1) {
    return lval_take(v, 0);
  }

  lval* f = lval_pop(v, 0);
  if (f->type != LVAL_SYM) {
    lval_del(f);
    lval_del(v);
    return lval_err("S-expression does not start with symbol!");
  }

  lval* result = builtin_op(v, f->sym);
  lval_del(f);
  return result;
}

lval* lval_eval(lval* v) {
  if (v->type == LVAL_SEXPR) {
    return lval_eval_sexpr(v);
  }
  return v;
}

lval* lval_read_num(mpc_ast_t* t) {
  errno = 0;
  long x = strtol(t->contents, NULL, 10);
  return errno != ERANGE ? lval_num(x) : lval_err("invalid number");
}

lval* lval_read(mpc_ast_t* t) {
  if (strstr(t->tag, "number")) {
    return lval_read_num(t);
  }
  if (strstr(t->tag, "symbol")) {
    return lval_sym(t->contents);
  }

  lval* x = NULL;
  if (strcmp(t->tag, ">") == 0) {
    x = lval_sexpr();
  }
  if (strstr(t->tag, "sexpr")) {
    x = lval_sexpr();
  }

  for (int i = 0; i < t->children_num; i++) {
    if (strcmp(t->children[i]->contents, "(") == 0) {
      continue;
    }
    if (strcmp(t->children[i]->contents, ")") == 0) {
      continue;
    }
    if (strcmp(t->children[i]->contents, "{") == 0) {
      continue;
    }
    if (strcmp(t->children[i]->contents, "}") == 0) {
      continue;
    }
    if (strcmp(t->children[i]->tag, "regex") == 0) {
      continue;
    }
    x = lval_add(x, lval_read(t->children[i]));
  }

  return x;
}

int main(int argc, char** argv) {
  mpc_parser_t* Number = mpc_new("number");
  mpc_parser_t* Symbol = mpc_new("symbol");
  mpc_parser_t* Sexpr  = mpc_new("sexpr");
  mpc_parser_t* Expr   = mpc_new("expr");
  mpc_parser_t* Lispy  = mpc_new("lispy");

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

  puts("Lispy Version 0.0.0.0.5");
  puts("Press Ctrl+c to Exit\n");

  while (1) {

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

    mpc_result_t r;
    if (mpc_parse("<stdin>", input, Lispy, &r)) {
      lval* x = lval_eval(lval_read(r.output));
      lval_println(x);
      lval_del(x);
      mpc_ast_delete(r.output);
    } else {
      mpc_err_print(r.error);
      mpc_err_delete(r.error);
    }

    free(input);

  }

  mpc_cleanup(5, Number, Symbol, Sexpr, Expr, Lispy);

  return 0;
}