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|
{-# LANGUAGE DeriveDataTypeable #-}
module Typecase1 (tests) where
{-
This test demonstrates type case as it lives in Data.Typeable.
We define a function f that converts typeables into strings in some way.
Note: we only need Data.Typeable. Say: Dynamics are NOT involved.
-}
import Test.Tasty.HUnit
import Data.Typeable
import Data.Maybe
-- Some datatype.
data MyTypeable = MyCons String deriving (Show, Typeable)
--
-- Some function that performs type case.
--
f :: (Show a, Typeable a) => a -> String
f a = (maybe (maybe (maybe others
mytys (cast a) )
float (cast a) )
int (cast a) )
where
-- do something with ints
int :: Int -> String
int a = "got an int, incremented: " ++ show (a + 1)
-- do something with floats
float :: Double -> String
float a = "got a float, multiplied by .42: " ++ show (a * 0.42)
-- do something with my typeables
mytys :: MyTypeable -> String
mytys a = "got a term: " ++ show a
-- do something with all other typeables
others = "got something else: " ++ show a
--
-- Test the type case
--
tests = ( f (41::Int)
, f (88::Double)
, f (MyCons "42")
, f True) @=? output
output = ( "got an int, incremented: 42"
, "got a float, multiplied by .42: 36.96"
, "got a term: MyCons \"42\""
, "got something else: True")
|
