then.cr

# simple railway-style pipelines for Crystal

class Success(T)
  def initialize(@value : T)
  end

  def then(callable : T -> Success(T) | Failure(T))
    callable.call(@value)
  end

  def then(callable : Proc(T, T))
    callable.call(@value)
  end

  def then(&block : T -> Success(T) | Failure(T))
    yield @value
  end
end

class Failure(T)
  def initialize(@value : T, @error : String)
  end

  def then(callable : T -> Success(T) | Failure(T))
    self
  end

  def then(callable : Proc(T, T))
    self
  end

  def then(&block : T -> Success(T) | Failure(T))
    self
  end
end

times_two = ->(v : Int32) { Success.new(v * 2) }

def validate(v : Int32)
  Failure.new(v, "nope")
end

pp Success.new(10)
  .then(->(v : Int32) { Success.new(v + 2) }) # with inline lambda
  .then(times_two) # with Proc
  .then(-> validate(Int32)) # with method object
  .then(->(v : Int32) { Success.new(v * 3) })
  .then { |v| Success.new(v * 10) } # with block