pipable.rb

# Elixir has pipes `|>`. Let's try to implement those in Ruby.
#
# I want to write this:
#
#   email.body | RemoveSignature | HighlightMentions | :html_safe
#
# instead of:
#
#   HighlightMentions.call(RemoveSignature.call(email.body)).html_safe
#

# Ugly implementation starts here...

def pipe_it(input, filter)
  # multiplexed input!
  if input.is_a? Array
    return input.map { |input_item| pipe_it(input_item, filter) }
  end

  case filter
  when Symbol
    input.send(filter)
  when Hash
    method = filter.keys.first
    arguments = Array(filter.values.first)
    input.send(method, *arguments)
  when Array
    # multiplex!
    filter.map { |filter_item| pipe_it(input, filter_item) }
  else
    filter.call(input)
  end
end

class Pipeline
  def initialize(*filters)
    @filters = filters
  end

  attr_accessor :filters

  def call(input)
    filters.inject(input) do |input, filter|
      pipe_it(input, filter)
    end
  end
end

def pipable(input)
  input.define_singleton_method(:|) do |filter|
    pipable pipe_it(input, filter)
  end

  input
end

def pipe(input, *pipeline)
  Pipeline.new(*pipeline).call(input)
end

# Let's define a few filters

Reverse = ->(string) { string.reverse }
Leet    = ->(string) { string.gsub(/[aeiost]/,'a'=>'4','e'=>'3','i'=>'1','o'=>'0','s'=>'5','t'=>'7') }
Mooify  = ->(string) { "Cow said: " + string }
Say     = ->(string) { system %|say "#{string}"|; string }

TweetTo = Struct.new(:recipient) do
  def call(input)
    puts %|Tweeting "#{input}" to #{@recipient}!|
    input
  end
end

# Time to play with different approaches...

# 1 - We make the first element pipable and we can then just pipe through!
result = pipable("moo") | Reverse | Leet | Mooify | :downcase | TweetTo.new('@pcreux') | { delete: 'o' }
puts result
# => cw said: 00m

# 2 - Pipe without defining any `|` method
puts pipe("moo", Mooify, :upcase)
# => COW SAID: MOO

# 3 - Pipeline object
pipeline = Pipeline.new(Mooify, :downcase, { gsub: ["o", "a"] })

pipeline.filters << ->(input) { input.gsub("moo", "maow") }

puts pipeline.call("moo")
# => caw said: maa

pipeline.filters.reverse!

puts pipeline.call("moo")
# => Cow said: maaw

# ZOMG! Multiplexing!
# "moo" => Mooify => :downcase => Reverse
#                 => :upcase   => Reverse
p Pipeline.new(Mooify, [:downcase, :upcase], Reverse).call("moo")
# => ["oom :dias woc", "OOM :DIAS WOC"]

# Multi-Multiplexing... let me tell you...
p Pipeline.new(Mooify, [:downcase, :upcase], Reverse, [:reverse, Leet]).call("moo")
# => [["cow said: moo", "00m :d145 w0c"], ["COW SAID: MOO", "OOM :DIAS WOC"]]