On Fri, Jan 22, 2010 at 04:47:14PM +0000, Dominic Mulligan wrote:

Dear Brent,

Thanks for the reply. The type of args is [Type a]. Ascribing a specific type, like so:

prop_InjectTypeConFreeVars :: [Type String] -> Bool prop_InjectTypeConFreeVars args = (freeTypeVars . (tyCon "Fun")) args == (concatMap freeTypeVars args)

Leads to the same problem; quickCheck is brought to its knees after about 6 tests.

I suspect what is happening here is that 'Type' is recursive and QuickCheck is going crazy generating huge deeply nested random types. This is rather a failing of QuickCheck. For the current state of the art in QuickCheck for recursive data types, see "Generating Recursive Data Types" here: http://www.cs.chalmers.se/~rjmh/QuickCheck/manual.html although even this leaves a lot to be desired. There is actually ongoing research (by me and others) into improving the situation. -Brent