cpure_NP example

cpure_NP.hs

{-# LANGUAGE DataKinds, TypeApplications #-}
-- http://hackage.haskell.org/package/sop-core
module Main where

import Data.SOP
import Data.SOP.NP (cpure_NP,cliftA_NP,collapse_NP)
import Data.Default
import Data.Proxy

-- NP is an n-ary product indexed by a type-level list. Each value is wrapped in an identity functor I.
defaults :: NP I '[Int, Float]
defaults = cpure_NP (Proxy @Default) (I def)

-- cliftA_NP lets us use Show for transforming the components of the product.
-- mapIK is an auxiliary function for transforming I-wrapped values to K-wrapped values. 
-- K is a constant functor with an annotation that lets us store values (Strings here) unrelated to the field's type.
main :: IO ()
main = print $ collapse_NP $ cliftA_NP (Proxy @Show) (mapIK show) defaults