Collections of lambda for processing data in a functionnal way

data_fns.rb

class Object
  def _(fn)
    fn.(self)
  end
end

module DataFn
  class DoubleEntries < StandardError
  end

  mattr_reader :count_by, :index_by, :h_fmap, :at, :attr, :attrs

  @@count_by = ->fn, a {
    a.reduce({}) do |memo, a|
      key = fn.(a)
      memo[key] ||= 0
      memo[key] += 1
      memo
    end
  }.curry

  @@index_by = ->fn, a {
    a.reduce({}) do |memo, a|
      res = fn.(a)
      if memo[res]
        raise DoubleEntries
      else
        memo[res] = a
      end
      memo
    end
  }.curry

  @@h_fmap = ->fn, a {
    a.reduce({}) do |memo, (k, v)|
      memo[k] ||= fn.(v)
      memo
    end
  }.curry

  @@at = ->key, a {
    a.fetch(key)
  }.curry

  @@attr = ->method, a {
    a.send(method)
  }.curry

  @@attrs = ->defn, a {
    defn.inject({}) do |memo, (method, fn)|
      memo[method] ||= fn.(attr.(method).(a))
      memo
    end
  }.curry
end

include DataFn