module Arrows

# File lib/arrows.rb, line 62
def arrow_like?(x)
   proc_like?(x) && 
   x.arity == 1 && 
   x.respond_to?(:>=) && 
   x.respond_to?(:>>) && 
   x.respond_to?(:^) && 
   x.respond_to?(:/) && 
   x.respond_to?(:%)
end

# File lib/arrows.rb, line 37
def compose(f,g)
  Arrows::Proc.new { |args| g[f[args]] }
end

# File lib/arrows.rb, line 29
def concurrent(f,g)
  Arrows::Proc.new do |args| 
    [f[args.first], g[args.last]]
  end
end

# File lib/arrows.rb, line 47
def evil(x=nil)
  return x if x.respond_to?(:good?) && x.respond_to?(:payload)
  Arrows::Either.new false, x
end

# File lib/arrows.rb, line 21
def evil_fork(g)
  fork ID, g
end

# File lib/arrows.rb, line 34
def fanout(f,g)
  Arrows::Proc.new { |args| [f[args], g[args]] }
end

# File lib/arrows.rb, line 7
def feedback(merge, split)
  Arrows::Proc.new do |args|
    single = merge.call [args]
    either = split.call single
    while not either.good?
      single = merge.call either.payload
      either = split.call single
    end
    either.payload
  end
end

# File lib/arrows.rb, line 40
def fmap(xs, f)
  Arrows::Proc.new { |args| xs[args].map { |x| f[x] }  }
end

# File lib/arrows.rb, line 24
def fork(f,g)
  Arrows::Proc.new do |either|
    either.good? ? f[either.payload] : g[either.payload]
  end
end

# File lib/arrows.rb, line 43
def good(x=nil)
  return x if x.respond_to?(:good?) && x.respond_to?(:payload)
  Arrows::Either.new true, x
end

# File lib/arrows.rb, line 18
def good_fork(f)
  fork f, ID
end

# File lib/arrows.rb, line 51
def lift(x=nil)
  return Arrows::Proc.new { |args| yield args } if block_given?
  return x if arrow_like? x
  return wrap_proc x if proc_like? x
  Arrows::Proc.new { |args| x }
end

# File lib/arrows.rb, line 57
def polarize(x=nil)
  return lift { |args| yield(args) ? good(args) : evil(args) } if block_given?
  return lift { |args| x.call(args) ? good(args) : evil(args) } if proc_like? x
  lift { |args| x ? good(args) : evil(args) }
end

# File lib/arrows.rb, line 71
def proc_like?(x)
  x.respond_to?(:call) && x.respond_to?(:arity)
end

# File lib/arrows.rb, line 74
def wrap_proc(f)
  Arrows::Proc.new do |args|
    f[args]
  end
end