On 12 November 2013 09:31, Graham Berks
Hi, have the following type
data BinomialHeap a = EmptyHeap | Node a Int (BinomialHeap a)
and wanted to create a test generator with type ‘a’ as an Int for example
hence had
newtype BinominalHeapInt = BinominalHeap Int deriving (Eq, Show)
Methinks this line is an error: what you've said is that BinominalHeapInt is an Int wrapped in a BinominalHeap constructor; you probably want: newtype BinomialHeapInt = BHI (BinomialHeap Int) Notice also your type of "Binominal" instead of "Binomial". (You can't derive anything as Eq and Show aren't derived/defined for BinomialHeap)
But struggling to get the generator correct, currently have
instance Arbitrary BinominalHeapInt where arbitrary = sized heap' where heap' 0 = return EmptyHeap heap' n | n>0 = oneof [return EmptyHeap, liftM3 Node arbitrary arbitrary subnode] where subnode = heap' (n `div` 2)
What you'd probably want is to have "instance (Arbitrary a) => Arbitrary (BinomialHeap a) where ..." with this definition, and then: instance Arbitrary BinomialHeapInt where arbitrary = fmap BHI arbitrary
But it complains
Expected type: Int -> Gen BinominalHeapInt Actual type: Int -> Gen (BinomialHeap a1)
in sized heap’
Any pointers ?
Thanks
_______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
-- Ivan Lazar Miljenovic Ivan.Miljenovic@gmail.com http://IvanMiljenovic.wordpress.com