/// Takes a function that takes two arguments and returns a new function that
/// takes the same two arguments, but in reverse order.
///
pub fn flip(fun: fn(a, b) -> c) -> fn(b, a) -> c {
  fn(b, a) { fun(a, b) }
}

/// Takes a single argument and always returns its input value.
///
pub fn identity(x: a) -> a {
  x
}

/// Takes an argument and a single function,
/// calls that function with that argument
/// and returns that argument instead of the function return value.
/// Useful for running synchronous side effects in a pipeline.
///
pub fn tap(arg: a, effect: fn(a) -> b) -> a {
  effect(arg)
  arg
}