{-# OPTIONS -fglasgow-exts #-}
module GZip (tests) where
{-
This test illustrates zipping for the company datatypes which we use a
lot. We process two companies that happen to agree on the overall
shape but differ in the salaries in a few positions. So whenever we
encounter salaries we take the maximum of the two.
-}
import Test.HUnit
import Data.Generics
import CompanyDatatypes
-- The main function which prints the result of zipping
tests = gzip (\x y -> mkTT maxS x y) genCom1 genCom2 ~=? output
-- NB: the argument has to be eta-expanded to match
-- the type of gzip's argument type, which is
-- GenericQ (GenericM Maybe)
where
-- Variations on the show case company "genCom"
genCom1 = everywhere (mkT (double "Joost")) genCom
genCom2 = everywhere (mkT (double "Marlow")) genCom
double x (E p@(P y _) (S s)) | x == y = E p (S (2*s))
double _ e = e
-- Sum up two salaries
maxS (S x) (S y) = S (max x y)
-- Make a two-arguments, generic function transformer
mkTT :: (Typeable a, Typeable b, Typeable c)
=> (a -> a -> a) -> b -> c -> Maybe c
mkTT (f::a -> a -> a) x y =
case (cast x,cast y) of
(Just (x'::a),Just (y'::a)) -> cast (f x' y')
_ -> Nothing
output = Just (C [D "Research" (E (P "Laemmel" "Amsterdam") (S 8000.0))
[PU (E (P "Joost" "Amsterdam") (S 2000.0))
,PU (E (P "Marlow" "Cambridge") (S 4000.0))]
,D "Strategy" (E (P "Blair" "London") (S 100000.0)) []])