Operators for composition of endomorphism in Dart

endocompo.dart

// Here be dragons //
extension _EndomorphicComposition<T> on T Function(T) {
  /// Mathematical composition of endomorphisms.
  ///
  /// In mathematics, function composition is an operation ∘ that takes two
  /// functions ƒ and g, and produces a function h = g ∘ ƒ such that
  /// h(x) = g(ƒ(x)).
  ///
  /// An endomorphism is any morphism ƒ whose domain is equal to its codomain
  /// such that ƒ: a -> a or T ƒ(T)
  T Function(T) operator <<(T Function(T) f) => (x) => f(this(x));

  /// Forward composition of endomorphisms.
  T Function(T) operator >>(T Function(T) f) => (x) => this(f(x));
}

int plusOne(int x) => x + 1;
int mulTwo(int x) => x * 2;

void thing() {
  final xs = [1, 2, 3, 4];
  final ys = xs.map(plusOne >> mulTwo); // [4, 6, 8, 10]
  final zs = xs.map(plusOne << mulTwo); // [3, 5, 7, 9]
  print('$ys\n$zs');

  // imperatively
  var yys = <int>[];
  for (final x in xs) {
    // yys.add(mulTwo(plusOne(x)));
    final y = plusOne(x);
    final z = mulTwo(y);
    yys.add(z);
  }
}