Functional Staples, in ChucK

README.md

Functional Functions in ChucK

Here's a set of iterative solutions to map, reduce, and filter, in ChucK. Should probably have gone recursive. Next time.

Somewhat hampered by ChucK missing a higher-order function feature, and the fact that the ChucK type system doesn't support generics or typeclasses, so I implemented classes to wrap them from which they can be extended.

I'd almost consider attempting to implement higher-order functions in ChucK myself after this, except that I'd almost definitely need to do a lot of type-inference code.

functional.ck

fun int[] map (int a[], Function f) {
  int b[0];
  for (0 => int i; i < a.size(); i++) {
    b << f.apply(a[i]);
  }
  return b;
}

fun int reduce (int a[], reduceFunction f, int accumulator) {
  accumulator => int z;
  for (0 => int i; i < a.size(); i++) {
    z => int y;
    f.apply(a[i], y) => z;
  }
  return z;
}
fun int reduce (int a[], reduceFunction f) {
  return reduce (a, f, 0);
}

fun int[] filter ( int a[], Function f ) {
  int b[0];
  for (0 => int i; i < a.size(); i++) {
    if (f.apply(a[i])) {
      b << a[i];
    }
  }
  return b;
}

class Function {
  int default;
  fun int apply(int a){
    return default;
  }
}

class reduceFunction {
  int default;
  fun int apply(int a, int b) {
    return default;
  }
}

// The following is code to demonstrate the above functions

class Double extends Function {
  fun int apply(int a){
    return a * 2;
  }
}

class Sum extends reduceFunction {
  fun int apply(int a, int b) {
    return a + b;
  }
}

class IsEven extends Function {
  fun int apply(int a){
    if(a % 2 == 0){
      return 1;
    }
    else {
      return 0;
    }
  }
}

Double double;

Sum sum;

IsEven isEven;

map([1,2,3,4], double);   // [2,4,6,8]
reduce([1,2,3,4], sum);   // 10
filter([1,2,3,4],isEven); // [2,4]