#include <stdlib.h>
#include <stdio.h>

struct Int;
struct String;
struct Closure;
union Value;

enum Tag { VOID, INT, STRING, CLOSURE, CELL, ENV };

typedef union Value (*Lambda)() ;

struct Int {
  enum Tag t;
  int value;
};

struct String {
  enum Tag t;
  char* value;
};

struct Closure {
  enum Tag t;
  Lambda lam;
  void* env;
} ;

struct Env {
  enum Tag t;
  void* env;
};

struct Cell {
  enum Tag t;
  union Value* addr;
} ;

union Value {
  enum Tag t;
  struct Int z;
  struct String s;
  struct Closure clo;
  struct Env env;
  struct Cell cell;
} ;

typedef union Value Value;

static Value MakeClosure(Lambda lam, Value env) {
  Value v;
  v.clo.t = CLOSURE;
  v.clo.lam = lam;
  v.clo.env = env.env.env;
  return v;
}

static Value MakeInt(int n) {
  Value v;
  v.z.t = INT;
  v.z.value = n;
  return v;
}

static Value MakeString(char* s) {
  Value v;
  v.s.t = STRING;
  v.s.value = s;
  return v;
}

static Value MakePrimitive(Lambda prim) {
  Value v;
  v.clo.t = CLOSURE;
  v.clo.lam = prim;
  v.clo.env = NULL;
  return v;
}

static Value MakeEnv(void* env) {
  Value v;
  v.env.t = ENV;
  v.env.env = env;
  return v;
}


static Value NewCell(Value initialValue) {
  Value v;
  v.cell.t = CELL;
  v.cell.addr = malloc(sizeof(Value));
  *v.cell.addr = initialValue;
  return v;
}


Value sum(Value a, Value b) {
  return MakeInt(a.z.value + b.z.value);
}

Value product(Value a, Value b) {
  return MakeInt(a.z.value * b.z.value);
}

Value difference(Value a, Value b) {
  return MakeInt(a.z.value - b.z.value);
}

Value display(Value v) {
  printf("%i\n",v.z.value);
  return v;
}

Value equal(Value a, Value b) {
  return MakeInt(a.z.value == b.z.value);
}