test.lox

// Fibonacci
fun fib(n) {
  if (n <= 1) return n;
  return fib(n - 2) + fib(n - 1);
}

for (var i = 0; i < 20; i = i + 1) {
  print fib(i);
}

// Church Neumerals

// Zero is the identity function.
fun zero(f)
{
    fun identity(x)
    {
        return x;
    }

    return identity;
};

// Successor: apply function one more time.
fun succ(n)
{
    fun succF(f)
    {
        fun succX(x)
        {
            return f(n(f)(x));
        }
        return succX;
    }
    return succF;
}

fun plusOne(x)
{
    return x + 1;
}

// Convert a Church numeral into a concrete integer.
fun churchToInt(n)
{
    return n(plusOne)(0);
}

// Convert a concrete integer into a church numeral.
fun nToChurch(n) 
{
    if(n == 0)
    {
        return zero;
    }
    else
    {
        return succ(nToChurch(n - 1));
    }
}

// Add two Church numerals.
fun add(m)
{
    fun addN(n)
    {
        fun addF(f)
        {
            fun addX(x)
            {
                return n(f)(m(f)(x));
            }
            return addX;
        }
        return addF;
    }
    return addN;
}

// Multiply two Church numerals.
fun mul(m)
{
    fun mulN(n)
    {
        fun mulF(f)
        {
            fun mulX(x)
            {
                return n(m(f))(x);
            }
            return mulX;
        }
        return mulF;
    }
    return mulN;
}

fun exp(m)
{
    fun expN(n)
    {
        return n(m);
    }
    return expN;
}

var one = succ(zero);
var two = succ(one);
var three = succ(two);

print churchToInt(one);
print churchToInt(two);
print churchToInt(three);

print churchToInt(nToChurch(999));
print churchToInt(add(two)(two));
print churchToInt(mul(three)(three));
print churchToInt(exp(three)(three));