function style

functionstyle.d

module functionstyle;

import std.stdio;

T delegate(T) zero(T)(T delegate(T) f)
{
    T ret(T x)
    {
        return x;
    }
    return &ret;
}

T delegate(T) delegate(T delegate(T)) succ(T)(T delegate(T) delegate(T delegate(T)) n)
{
    T delegate(T) ret(T delegate(T) f)
    {
        T eval (T x)
        {
            return f(n(f)(x));
        }
        return &eval;
    }
    return &ret;
}

uint succ_uint(uint x)
{
    return x+1;
}

T delegate(T) delegate_from_function(T) (T function(T) f)
{
    T ret(T x)
    {
        return f(x);
    }
    return &ret;
}


void unit_test()
{
    auto n = delegate_from_function(&zero!uint);
    foreach (i; 0..10)
    {
        writefln("i = %d: f(0) = %d", i, n(delegate_from_function(&succ_uint))(0));
        n = succ(n);
    }
}