Dart pattern matching like Rust

main.dart

typedef bool Case<T>(T input);
Case<num> gt(num than) => (num x) => x != null && x > than;
Case nil = (instance) => instance == null;

O match<T, O>(T input, Map<dynamic, Function> cases) {
  for (final _case in cases.keys) {
    if (_case == input || (_case is Function && _case(input) == true)) {
      return cases[_case]();
    }
  }
  throw new RangeError('no matching case');
}

void main() {
  final list = [null, 10, 100];
  for (final x in list) {
    print(match(x, {
      10: () => 'x is 10!',
      gt(10): () => 'x is greater than 10!',
      nil: () => 'x is null'
    }));
  }
}