[Haskell-cafe] Re: QuickCheck: Arbitrary for a complex type

[Fawzi Mohamed]

Joel Reymont wrote:
> I got this simple example working so I think I have my question answered.
Great, just one thing that could be important : when you have recursive 
structures (like your Statement through Compound) be sure to use
sized (\mySize -> ...)
as generator for arbitrary so that you can avoid infinite looping.
Look at
  http://www.cs.chalmers.se/~rjmh/QuickCheck/manual_body.html#15
for an example.

Fawzi
>
> Now I just have to learn to write generators of my own to produce 
> valid and invalid input for my parser.
>
> module Foo where
>
> import Control.Monad
> import System.Random
> import Test.QuickCheck
>
> data Foo
>     = Foo Int
>     | Bar
>     | Baz
>       deriving Show
>
> instance Arbitrary Foo where
>     coarbitrary = undefined
>     arbitrary   = oneof [ return Bar
>                         , return Baz
>                         , liftM Foo arbitrary
>                         ]
>
> gen' rnd = generate 10000 rnd $ vector 5 :: [Foo]
>
> gen =
>     do { rnd <- newStdGen
>        ; return $ gen' rnd
>        }
>
> -- 
> http://wagerlabs.com/
>
>
>
>
>
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