// File: Hof.cs
// Author: David Bergman
//
// This file implements a mini framework for higher-order
// functions that I implemented during a seminar at Lab49

using System.Collections.Generic;


public class Hof {
public delegate R Fun1<R, A>(A n);
public delegate R Fun2<R, A1, A2>(A1 a1, A2 a2);

// This function adapter combines two functions.
// This is called "function composition" in FP-land.
public static Fun1<T3, T1> Comp<T1, T2, T3>(
   Fun1<T3, T2> fun1, Fun1<T2, T1> fun2)
{
  return delegate(T1 t) { return fun1(fun2(t)); }
}

public static void Transform<T1, T2>(IEnumerable<T1> seq,
			     IList<T2> dest,
			     Fun1<T2, T1> fun
			     ) {
  foreach (T1 t in seq)
    dest.Add(fun(t));
} 

public static T Accumulate<T>(IEnumerable<T> seq, T start,
			      Fun2<T, T, T> fun) {
  T accum = start;
  foreach (T t in seq)
    accum = fun(accum, t);
  return accum;
}
}