juxtapose.rb

juxt = ->(*fns) do
  ->(*args) do 
    fns.map do |fn|
      args.reduce {|acc, e| fn.to_proc.call acc, e}
    end
  end
end

max = ->(a, b) {a > b ? a : b}
min = ->(a, b) {a < b ? a : b}

juxt.(:+, max, min).(2, 3, 5, 1, 6, 4)

# => [21, 6, 1]

filter = ->(fn, list) {list.find_all {|e| fn.to_proc.call e}}
remove = ->(fn, list) {list.find_all {|e| !fn.to_proc.call e}}

# partition things, strangely
juxt.(filter, remove).(:even?, [1, 2, 3, 4, 5, 6])

# => [[2, 4, 6], [1, 3, 5]]


# works, but we need to rewrite everything in terms of reduce. kind of a bummer. let's try to take advantage of Enumerable and Array!

juxt2 = ->(*fns) do
  ->(*args) do 
    fns.map do |fn, *options|
      args.send fn, *options
    end
  end
end

# less work...

juxt2.([:reduce, :+], :max, :min).(1, 2, 3, 4, 5, 6)

# but how do we pull off our fun filtering trick? one possibility:

juxt3 = ->(*fns) do
  ->(*args) do 
    fns.map do |fn, *options|
      options.empty? ? args.send(fn) : eval("#{args}.#{fn}(&:#{options.first})")
    end
  end
end

juxt3.([:find_all, :even?], [:find_all, :odd?]).(1, 2, 3, 4, 5, 6)