Hi Neil and Sebastiaan, Thanks for the constructive criticism ;).
As far as i can tell, derive only works for regular and linear recursive types and Regular uses frequencies to regulate size. (Also Regular doesn't seem to work for QuickCheck-2). I think I may have used a too simple example in my original post. Here is a more complicated one: >data TrinaryTree a = > Branch a (TrinaryTree a) (TrinaryTree a) (TrinaryTree a) > | Empty deriving Show > >$(agatath $ derive ''TrinaryTree) With the derive tool, generated values would typically be infinite. With Regular, the user would need to specify frequencies, and even then the generator would be useless because of the low frequency required for "Branch" to ensure termination (most generated trees would be empty, and almost none would contain several branches). Most of the work i have done on Agata is to make a class that resembles arbitrary (i.e. can be used to construct generators) but where the instances can be defined mechanically from the definition of instantiated types. The reason i didn't use Generics for defining the instances is that I was unsure if/how it distinguishes mutually recursive fields. Another feature of Agata generators is improved scalability compared to other QuickCheck generators, especially for nested collection data types (analog to [[[[a]]]] and such). The details of how this works in Agata will one day be explained in the documentation, but the principle is explained in my masters thesis[1]. Regards, Jonas [1] http://gupea.ub.gu.se/bitstream/2077/22087/1/gupea_2077_22087_1.pdf 2010/4/20 Sebastiaan Visser <sfvis...@cs.uu.nl>: > 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 > > _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
