[Haskell-cafe] QuickCheck Arbitrary - infinite recursion on recursive GADTs?

Marc Weber marco-oweber at gmx.de
Mon Jun 4 22:40:20 EDT 2007


data A = A INt
       | B [A]

instace Arbitrary A where
  arbitrary = oneof [ liftM A arbitrary
                    , liftM B arbitrary

But now QuickCheck will propably create a test value
A ( B [ A ( B [ A .... -> no end

Is there an easy QuickCheck way to prevent this?

I can think of:
a) using sized to pass when to stop (decrement the value ..)
b) using some type hackary
  data Recursive a = R a
  then use arbitrary :: R ( R ( a ))
   and remove one R each time..
c) pass a recursion indicator manually and decrement that...
Which would you choose?


More information about the Haskell-Cafe mailing list