On Tue, Apr 7, 2009 at 6:11 PM, Brad Larsen
prop_insert_idempotent :: (Eq d, PrefixDict d) => d -> Word -> Bool prop_insert_idempotent d w = insert w d' == d' where d' = insert w d
The problem is this: I can't think of a non-kludged way of checking that TrieDict and ListDict satisfy this abstract property without having to add explicit type signatures, e.g.
quickCheck (prop_insert_idempotent :: TrieDict -> Word -> Bool)
This is one place where parametrized modules would come in handy. There hasn't been a good proposal to implement these in Haskell; in particular it's not clear how they should interact with typeclasses. You can do something like this:
data Proxy d = Proxy
-- add any other constraints required by your test properties here data CheckPrefixDict = forall d. (PrefixDict d, Eq d, Show d, Arbitrary d) => CheckPrefixDict (Proxy d)
prop_insert_idempotent :: CheckPrefixDict -> Property prop_insert_idempotent (CheckPrefixDict (Proxy :: Proxy d)) = property prop where prop :: d -> Word -> Bool prop d w = insert w d' == d' where d' == insert w d
checkableTrie = CheckPrefixDict (Proxy :: Proxy TrieDict)
You then can "quickCheck (prop_insert_idempotent checkableTrie)" Or if you want to test all your structures at once, make CheckPrefixDict an instance of Arbitrary that selects one of the implementations randomly. (In this case you probably want to add a descriptive string so that when a test fails you know which instance has the problem :) -- ryan