Interesting. Would be used like this: uniquePermutations xs = runST $ strictToLazyST $ (uniquePermutationsST xs) After also swapping `runST` to the lazy version, it compiles and runs. Thank you! -----Original Message----- From: Peter Gammie [mailto:peteg42@gmail.com] Sent: Mittwoch, 22. Juli 2009 01:25 To: Christian Klauser Cc: glasgow-haskell-users@haskell.org Subject: Re: "Could not deduce (MArray (STUArray s) Int (ST s)) from context ()" when applying runST On 22/07/2009, at 9:16 AM, Christian Klauser wrote:
Thank you, works indeed with the strict ST monad. Didn't think of that. But makes kind of sense not to define these instances, since unboxed values cannot have their computation delayed. It's a bit unfortunate, however, that a single use of an unboxed array "forces" the whole state thread to become strict.
Hmm. Have you seen the strictToLazyST function? http://www.haskell.org/ghc/docs/latest/html/libraries/base/Control-Monad-ST- Lazy.html#v%3AstrictToLazyST cheers peter