Reference

conditionals.c

#include "mpc.h"
#ifdef _WIN32
static char buffer[2048];
char* readline(char* prompt) {
  fputs(prompt, stdout);
  fgets(buffer, 2048, stdin);
  char* cpy = malloc(strlen(buffer)+1);
  strcpy(cpy, buffer);
  cpy[strlen(cpy)-1] = '\0';
  return cpy;
}
void add_history(char* unused) {}
#else
#include <editline/readline.h>
#include <editline/history.h>
#endif
/* Forward Declarations */
struct lval;
struct lenv;
typedef struct lval lval;
typedef struct lenv lenv;
/* Lisp Value */
enum { LVAL_ERR, LVAL_NUM, LVAL_SYM, LVAL_FUN, LVAL_SEXPR, LVAL_QEXPR };
typedef lval*(*lbuiltin)(lenv*, lval*);
struct lval {
  int type;
  /* Basic */
  long num;
  char* err;
  char* sym;
  /* Function */
  lbuiltin builtin;
  lenv* env;
  lval* formals;
  lval* body;
  /* Expression */
  int count;
  lval** cell;
};
lval* lval_num(long x) {
  lval* v = malloc(sizeof(lval));
  v->type = LVAL_NUM;
  v->num = x;
  return v;
}
lval* lval_err(char* fmt, ...) {
  lval* v = malloc(sizeof(lval));
  v->type = LVAL_ERR;  
  va_list va;
  va_start(va, fmt);  
  v->err = malloc(512);  
  vsnprintf(v->err, 511, fmt, va);  
  v->err = realloc(v->err, strlen(v->err)+1);
  va_end(va);  
  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_builtin(lbuiltin func) {
  lval* v = malloc(sizeof(lval));
  v->type = LVAL_FUN;
  v->builtin = func;
  return v;
}
lenv* lenv_new(void);
lval* lval_lambda(lval* formals, lval* body) {
  lval* v = malloc(sizeof(lval));
  v->type = LVAL_FUN;  
  v->builtin = NULL;  
  v->env = lenv_new();  
  v->formals = formals;
  v->body = body;
  return v;  
}
lval* lval_sexpr(void) {
  lval* v = malloc(sizeof(lval));
  v->type = LVAL_SEXPR;
  v->count = 0;
  v->cell = NULL;
  return v;
}
lval* lval_qexpr(void) {
  lval* v = malloc(sizeof(lval));
  v->type = LVAL_QEXPR;
  v->count = 0;
  v->cell = NULL;
  return v;
}
void lenv_del(lenv* e);
void lval_del(lval* v) {
  switch (v->type) {
    case LVAL_NUM: break;
    case LVAL_FUN: 
      if (!v->builtin) {
        lenv_del(v->env);
        lval_del(v->formals);
        lval_del(v->body);
      }
    break;
    case LVAL_ERR: free(v->err); break;
    case LVAL_SYM: free(v->sym); break;
    case LVAL_QEXPR:
    case LVAL_SEXPR:
      for (int i = 0; i < v->count; i++) {
        lval_del(v->cell[i]);
      }
      free(v->cell);
    break;
  }
  free(v);
}
lenv* lenv_copy(lenv* e);
lval* lval_copy(lval* v) {
  lval* x = malloc(sizeof(lval));
  x->type = v->type;
  switch (v->type) {
    case LVAL_FUN:
      if (v->builtin) {
        x->builtin = v->builtin;
      } else {
        x->builtin = NULL;
        x->env = lenv_copy(v->env);
        x->formals = lval_copy(v->formals);
        x->body = lval_copy(v->body);
      }
    break;
    case LVAL_NUM: x->num = v->num; break;
    case LVAL_ERR: x->err = malloc(strlen(v->err) + 1);
      strcpy(x->err, v->err);
    break;
    case LVAL_SYM: x->sym = malloc(strlen(v->sym) + 1);
      strcpy(x->sym, v->sym);
    break;
    case LVAL_SEXPR:
    case LVAL_QEXPR:
      x->count = v->count;
      x->cell = malloc(sizeof(lval*) * x->count);
      for (int i = 0; i < x->count; i++) {
        x->cell[i] = lval_copy(v->cell[i]);
      }
    break;
  }
  return x;
}
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_join(lval* x, lval* y) {  
  for (int i = 0; i < y->count; i++) {
    x = lval_add(x, y->cell[i]);
  }
  free(y->cell);
  free(y);  
  return x;
}
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_print_expr(lval* v, char open, char close) {
  putchar(open);
  for (int i = 0; i < v->count; i++) {
    lval_print(v->cell[i]);    
    if (i != (v->count-1)) {
      putchar(' ');
    }
  }
  putchar(close);
}
void lval_print(lval* v) {
  switch (v->type) {
    case LVAL_FUN:
      if (v->builtin) {
        printf("<builtin>");
      } else {
        printf("(\\ ");
        lval_print(v->formals);
        putchar(' ');
        lval_print(v->body);
        putchar(')');
      }
    break;
    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_print_expr(v, '(', ')'); break;
    case LVAL_QEXPR: lval_print_expr(v, '{', '}'); break;
  }
}
void lval_println(lval* v) { lval_print(v); putchar('\n'); }
int lval_eq(lval* x, lval* y) {
  /* Different Types are always unequal */
  if (x->type != y->type) { return 0; }
  /* Compare Based upon type */
  switch (x->type) {
    /* Compare Number Value */
    case LVAL_NUM: return (x->num == y->num);
    /* Compare String Values */
    case LVAL_ERR: return (strcmp(x->err, y->err) == 0);
    case LVAL_SYM: return (strcmp(x->sym, y->sym) == 0);
    /* If Builtin compare functions, otherwise compare formals and body */
    case LVAL_FUN:
      if (x->builtin || y->builtin) {
        return x->builtin == y->builtin;
      } else {
        return lval_eq(x->formals, y->formals) && lval_eq(x->body, y->body);
      }
    /* If list compare every individual element */
    case LVAL_QEXPR:
    case LVAL_SEXPR:
      if (x->count != y->count) { return 0; }
      for (int i = 0; i < x->count; i++) {
        /* If any element not equal then whole list not equal */
        if (!lval_eq(x->cell[i], y->cell[i])) { return 0; }
      }
      /* Otherwise lists must be equal */
      return 1;
    break;
  }
  return 0;
}
char* ltype_name(int t) {
  switch(t) {
    case LVAL_FUN: return "Function";
    case LVAL_NUM: return "Number";
    case LVAL_ERR: return "Error";
    case LVAL_SYM: return "Symbol";
    case LVAL_SEXPR: return "S-Expression";
    case LVAL_QEXPR: return "Q-Expression";
    default: return "Unknown";
  }
}
/* Lisp Environment */
struct lenv {
  lenv* par;
  int count;
  char** syms;
  lval** vals;
};
lenv* lenv_new(void) {
  lenv* e = malloc(sizeof(lenv));
  e->par = NULL;
  e->count = 0;
  e->syms = NULL;
  e->vals = NULL;
  return e;
}
void lenv_del(lenv* e) {
  for (int i = 0; i < e->count; i++) {
    free(e->syms[i]);
    lval_del(e->vals[i]);
  }  
  free(e->syms);
  free(e->vals);
  free(e);
}
lenv* lenv_copy(lenv* e) {
  lenv* n = malloc(sizeof(lenv));
  n->par = e->par;
  n->count = e->count;
  n->syms = malloc(sizeof(char*) * n->count);
  n->vals = malloc(sizeof(lval*) * n->count);
  for (int i = 0; i < e->count; i++) {
    n->syms[i] = malloc(strlen(e->syms[i]) + 1);
    strcpy(n->syms[i], e->syms[i]);
    n->vals[i] = lval_copy(e->vals[i]);
  }
  return n;
}
lval* lenv_get(lenv* e, lval* k) {
  for (int i = 0; i < e->count; i++) {
    if (strcmp(e->syms[i], k->sym) == 0) { return lval_copy(e->vals[i]); }
  }
  if (e->par) {
    return lenv_get(e->par, k);
  } else {
    return lval_err("Unbound Symbol '%s'", k->sym);
  }
}
void lenv_put(lenv* e, lval* k, lval* v) {
  for (int i = 0; i < e->count; i++) {
    if (strcmp(e->syms[i], k->sym) == 0) {
      lval_del(e->vals[i]);
      e->vals[i] = lval_copy(v);
      return;
    }
  }
  e->count++;
  e->vals = realloc(e->vals, sizeof(lval*) * e->count);
  e->syms = realloc(e->syms, sizeof(char*) * e->count);  
  e->vals[e->count-1] = lval_copy(v);
  e->syms[e->count-1] = malloc(strlen(k->sym)+1);
  strcpy(e->syms[e->count-1], k->sym);
}
void lenv_def(lenv* e, lval* k, lval* v) {
  while (e->par) { e = e->par; }
  lenv_put(e, k, v);
}
/* Builtins */
#define LASSERT(args, cond, fmt, ...) \
  if (!(cond)) { lval* err = lval_err(fmt, ##__VA_ARGS__); lval_del(args); return err; }
#define LASSERT_TYPE(func, args, index, expect) \
  LASSERT(args, args->cell[index]->type == expect, \
    "Function '%s' passed incorrect type for argument %i. Got %s, Expected %s.", \
    func, index, ltype_name(args->cell[index]->type), ltype_name(expect))
#define LASSERT_NUM(func, args, num) \
  LASSERT(args, args->count == num, \
    "Function '%s' passed incorrect number of arguments. Got %i, Expected %i.", \
    func, args->count, num)
#define LASSERT_NOT_EMPTY(func, args, index) \
  LASSERT(args, args->cell[index]->count != 0, \
    "Function '%s' passed {} for argument %i.", func, index);
lval* lval_eval(lenv* e, lval* v);
lval* builtin_lambda(lenv* e, lval* a) {
  LASSERT_NUM("\\", a, 2);
  LASSERT_TYPE("\\", a, 0, LVAL_QEXPR);
  LASSERT_TYPE("\\", a, 1, LVAL_QEXPR);
  for (int i = 0; i < a->cell[0]->count; i++) {
    LASSERT(a, (a->cell[0]->cell[i]->type == LVAL_SYM),
      "Cannot define non-symbol. Got %s, Expected %s.",
      ltype_name(a->cell[0]->cell[i]->type), ltype_name(LVAL_SYM));
  }
  lval* formals = lval_pop(a, 0);
  lval* body = lval_pop(a, 0);
  lval_del(a);
  return lval_lambda(formals, body);
}
lval* builtin_list(lenv* e, lval* a) {
  a->type = LVAL_QEXPR;
  return a;
}
lval* builtin_head(lenv* e, lval* a) {
  LASSERT_NUM("head", a, 1);
  LASSERT_TYPE("head", a, 0, LVAL_QEXPR);
  LASSERT_NOT_EMPTY("head", a, 0);
  lval* v = lval_take(a, 0);  
  while (v->count > 1) { lval_del(lval_pop(v, 1)); }
  return v;
}
lval* builtin_tail(lenv* e, lval* a) {
  LASSERT_NUM("tail", a, 1);
  LASSERT_TYPE("tail", a, 0, LVAL_QEXPR);
  LASSERT_NOT_EMPTY("tail", a, 0);
  lval* v = lval_take(a, 0);  
  lval_del(lval_pop(v, 0));
  return v;
}
lval* builtin_eval(lenv* e, lval* a) {
  LASSERT_NUM("eval", a, 1);
  LASSERT_TYPE("eval", a, 0, LVAL_QEXPR);
  lval* x = lval_take(a, 0);
  x->type = LVAL_SEXPR;
  return lval_eval(e, x);
}
lval* builtin_join(lenv* e, lval* a) {
  for (int i = 0; i < a->count; i++) {
    LASSERT_TYPE("join", a, i, LVAL_QEXPR);
  }
  lval* x = lval_pop(a, 0);
  while (a->count) {
    lval* y = lval_pop(a, 0);
    x = lval_join(x, y);
  }
  lval_del(a);
  return x;
}
lval* builtin_op(lenv* e, lval* a, char* op) {
  for (int i = 0; i < a->count; i++) {
    LASSERT_TYPE(op, a, i, LVAL_NUM);
  }
  lval* x = lval_pop(a, 0);
  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* builtin_add(lenv* e, lval* a) { return builtin_op(e, a, "+"); }
lval* builtin_sub(lenv* e, lval* a) { return builtin_op(e, a, "-"); }
lval* builtin_mul(lenv* e, lval* a) { return builtin_op(e, a, "*"); }
lval* builtin_div(lenv* e, lval* a) { return builtin_op(e, a, "/"); }
lval* builtin_var(lenv* e, lval* a, char* func) {
  LASSERT_TYPE(func, a, 0, LVAL_QEXPR);
  lval* syms = a->cell[0];
  for (int i = 0; i < syms->count; i++) {
    LASSERT(a, (syms->cell[i]->type == LVAL_SYM),
      "Function '%s' cannot define non-symbol. "
      "Got %s, Expected %s.",
      func, ltype_name(syms->cell[i]->type), ltype_name(LVAL_SYM));
  }
  LASSERT(a, (syms->count == a->count-1),
    "Function '%s' passed too many arguments for symbols. "
    "Got %i, Expected %i.",
    func, syms->count, a->count-1);
  for (int i = 0; i < syms->count; i++) {
    if (strcmp(func, "def") == 0) { lenv_def(e, syms->cell[i], a->cell[i+1]); }
    if (strcmp(func, "=")   == 0) { lenv_put(e, syms->cell[i], a->cell[i+1]); } 
  }
  lval_del(a);
  return lval_sexpr();
}
lval* builtin_def(lenv* e, lval* a) { return builtin_var(e, a, "def"); }
lval* builtin_put(lenv* e, lval* a) { return builtin_var(e, a, "="); }
lval* builtin_ord(lenv* e, lval* a, char* op) {
  LASSERT_NUM(op, a, 2);
  LASSERT_TYPE(op, a, 0, LVAL_NUM);
  LASSERT_TYPE(op, a, 1, LVAL_NUM);
  int r;
  if (strcmp(op, ">")  == 0) {
    r = (a->cell[0]->num >  a->cell[1]->num);
  }
  if (strcmp(op, "<")  == 0) {
    r = (a->cell[0]->num <  a->cell[1]->num);
  }
  if (strcmp(op, ">=") == 0) {
    r = (a->cell[0]->num >= a->cell[1]->num);
  }
  if (strcmp(op, "<=") == 0) {
    r = (a->cell[0]->num <= a->cell[1]->num);
  }
  lval_del(a);
  return lval_num(r);
}
lval* builtin_gt(lenv* e, lval* a) {
  return builtin_ord(e, a, ">");
}
lval* builtin_lt(lenv* e, lval* a) {
  return builtin_ord(e, a, "<");
}
lval* builtin_ge(lenv* e, lval* a) {
  return builtin_ord(e, a, ">=");
}
lval* builtin_le(lenv* e, lval* a) {
  return builtin_ord(e, a, "<=");
}
lval* builtin_cmp(lenv* e, lval* a, char* op) {
  LASSERT_NUM(op, a, 2);
  int r;
  if (strcmp(op, "==") == 0) {
    r =  lval_eq(a->cell[0], a->cell[1]);
  }
  if (strcmp(op, "!=") == 0) {
    r = !lval_eq(a->cell[0], a->cell[1]);
  }
  lval_del(a);
  return lval_num(r);
}
lval* builtin_eq(lenv* e, lval* a) {
  return builtin_cmp(e, a, "==");
}
lval* builtin_ne(lenv* e, lval* a) {
  return builtin_cmp(e, a, "!=");
}
lval* builtin_if(lenv* e, lval* a) {
  LASSERT_NUM("if", a, 3);
  LASSERT_TYPE("if", a, 0, LVAL_NUM);
  LASSERT_TYPE("if", a, 1, LVAL_QEXPR);
  LASSERT_TYPE("if", a, 2, LVAL_QEXPR);
  /* Mark Both Expressions as evaluable */
  lval* x;
  a->cell[1]->type = LVAL_SEXPR;
  a->cell[2]->type = LVAL_SEXPR;
  if (a->cell[0]->num) {
    /* If condition is true evaluate first expression */
    x = lval_eval(e, lval_pop(a, 1));
  } else {
    /* Otherwise evaluate second expression */
    x = lval_eval(e, lval_pop(a, 2));
  }
  /* Delete argument list and return */
  lval_del(a);
  return x;
}
void lenv_add_builtin(lenv* e, char* name, lbuiltin func) {
  lval* k = lval_sym(name);
  lval* v = lval_builtin(func);
  lenv_put(e, k, v);
  lval_del(k); lval_del(v);
}
void lenv_add_builtins(lenv* e) {
  /* Variable Functions */
  lenv_add_builtin(e, "\\",  builtin_lambda); 
  lenv_add_builtin(e, "def", builtin_def);
  lenv_add_builtin(e, "=",   builtin_put);
  /* List Functions */
  lenv_add_builtin(e, "list", builtin_list);
  lenv_add_builtin(e, "head", builtin_head);
  lenv_add_builtin(e, "tail", builtin_tail);
  lenv_add_builtin(e, "eval", builtin_eval);
  lenv_add_builtin(e, "join", builtin_join);
  /* Mathematical Functions */
  lenv_add_builtin(e, "+", builtin_add);
  lenv_add_builtin(e, "-", builtin_sub);
  lenv_add_builtin(e, "*", builtin_mul);
  lenv_add_builtin(e, "/", builtin_div);
  /* Comparison Functions */
  lenv_add_builtin(e, "if",    builtin_if);
  lenv_add_builtin(e, "==",    builtin_eq);
  lenv_add_builtin(e, "!=",    builtin_ne);
  lenv_add_builtin(e, ">",  builtin_gt);
  lenv_add_builtin(e, "<",  builtin_lt);
  lenv_add_builtin(e, ">=", builtin_ge);
  lenv_add_builtin(e, "<=", builtin_le);
}
/* Evaluation */
lval* lval_call(lenv* e, lval* f, lval* a) {
  if (f->builtin) { return f->builtin(e, a); }
  int given = a->count;
  int total = f->formals->count;
  while (a->count) {
    if (f->formals->count == 0) {
      lval_del(a);
      return lval_err("Function passed too many arguments. "
        "Got %i, Expected %i.", given, total); 
    }
    lval* sym = lval_pop(f->formals, 0);
    if (strcmp(sym->sym, "&") == 0) {
      if (f->formals->count != 1) {
        lval_del(a);
        return lval_err("Function format invalid. "
          "Symbol '&' not followed by single symbol.");
      }
      lval* nsym = lval_pop(f->formals, 0);
      lenv_put(f->env, nsym, builtin_list(e, a));
      lval_del(sym); lval_del(nsym);
      break;
    }
    lval* val = lval_pop(a, 0);    
    lenv_put(f->env, sym, val);    
    lval_del(sym); lval_del(val);
  }
  lval_del(a);
  if (f->formals->count > 0 &&
    strcmp(f->formals->cell[0]->sym, "&") == 0) {
    if (f->formals->count != 2) {
      return lval_err("Function format invalid. "
        "Symbol '&' not followed by single symbol.");
    }
    lval_del(lval_pop(f->formals, 0));
    lval* sym = lval_pop(f->formals, 0);
    lval* val = lval_qexpr();    
    lenv_put(f->env, sym, val);
    lval_del(sym); lval_del(val);
  }
  if (f->formals->count == 0) {  
    f->env->par = e;    
    return builtin_eval(f->env, lval_add(lval_sexpr(), lval_copy(f->body)));
  } else {
    return lval_copy(f);
  }
}
lval* lval_eval_sexpr(lenv* e, lval* v) {
  for (int i = 0; i < v->count; i++) { v->cell[i] = lval_eval(e, 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_eval(e, lval_take(v, 0)); }
  lval* f = lval_pop(v, 0);
  if (f->type != LVAL_FUN) {
    lval* err = lval_err(
      "S-Expression starts with incorrect type. "
      "Got %s, Expected %s.",
      ltype_name(f->type), ltype_name(LVAL_FUN));
    lval_del(f); lval_del(v);
    return err;
  }
  lval* result = lval_call(e, f, v);
  lval_del(f);
  return result;
}
lval* lval_eval(lenv* e, lval* v) {
  if (v->type == LVAL_SYM) {
    lval* x = lenv_get(e, v);
    lval_del(v);
    return x;
  }
  if (v->type == LVAL_SEXPR) { return lval_eval_sexpr(e, v); }
  return v;
}
/* Reading */
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(); }
  if (strstr(t->tag, "qexpr"))  { x = lval_qexpr(); }
  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;
}
/* Main */
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* Qexpr  = mpc_new("qexpr");
  mpc_parser_t* Expr   = mpc_new("expr");
  mpc_parser_t* Lispy  = mpc_new("lispy");
  mpca_lang(MPCA_LANG_DEFAULT,
    "                                                     \
      number : /-?[0-9]+/ ;                               \
      symbol : /[a-zA-Z0-9_+\\-*\\/\\\\=<>!&]+/ ;         \
      sexpr  : '(' <expr>* ')' ;                          \
      qexpr  : '{' <expr>* '}' ;                          \
      expr   : <number> | <symbol> | <sexpr> | <qexpr> ;  \
      lispy  : /^/ <expr>* /$/ ;                          \
    ",
    Number, Symbol, Sexpr, Qexpr, Expr, Lispy);
  puts("Lispy Version 0.0.0.0.9");
  puts("Press Ctrl+c to Exit\n");
  lenv* e = lenv_new();
  lenv_add_builtins(e);
  while (1) {
    char* input = readline("lispy> ");
    add_history(input);
    mpc_result_t r;
    if (mpc_parse("<stdin>", input, Lispy, &r)) {
      lval* x = lval_eval(e, 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);
  }
  lenv_del(e);
  mpc_cleanup(6, Number, Symbol, Sexpr, Qexpr, Expr, Lispy);
  return 0;
}