Jonas, You can also derive (Co)Arbitrary instances automatically using the regular-extras package based on the Regular generic programming library. The advantage of using a library like Regular is that you do not have to write any Template Haskell code. The library generates a nice algebraic generic view on your datatype that you can use to write your generic functions. The Regular library itself of course uses TH internally, but this is done once and all datatype generic functions can piggy bag on the same TH derivation. For example, look at Generics.Regular.Functions.Arbitrary, this module is really concise. Nice work though! Gr, Sebastiaan On Apr 18, 2010, at 1:43 AM, Jonas Almström Duregård wrote:
I'm pleased to announce Agata (Agata Generates Algebraic Types Automatically)!
Avoiding excessive details, usage is best described by a small example:
{-#LANGUAGE TemplateHaskell #-} import Test.QuickCheck import Test.AgataTH
data X a b = X [Either a b] deriving Show data Y = Y deriving Show data Z = Z deriving Show
$(agatath $ deriveall [''X,''Y,''Z])
main = sample (arbitrary :: Gen (X Y Z))
This code derives instances of Test.QuickCheck.Arbitrary for the data types X, Y and Z.
http://hackage.haskell.org/package/Agata
Regards Jonas