Currying in Dart

main.dart

typedef R Fn1<R, T1>(T1 arg1);
typedef R Fn2<R, T1, T2>(T1 arg1, T2 arg2);

Fn1<Fn1<R, T2>, T1> curry12<R, T1, T2>(Fn2<R, T1, T2> fn) {
  return (T1 arg1) => (T2 arg2) => fn(arg1, arg2);
}

Fn1<Fn1<R, T1>, T2> curry21<R, T1, T2>(Fn2<R, T1, T2> fn) {
  return (T2 arg2) => (T1 arg1) => fn(arg1, arg2);
}

void append(String str, String append) => '$str$append';

void main() {
  final list = ['World!', 'Dart', 'Is there anybody there?'];
  list.map((str) => append('Hello, ', str)).forEach(print);
  list.map(curry12(append)('Hello, ')).forEach(print);
  list.map(curry21(append)('...')).forEach(print);
}