Hello, I just released threads-0.2. The library which lets you fork threads and wait for their result. INSTALL: $ cabal update $ cabal install threads API DOCS: http://hackage.haskell.org/package/threads-0.2 DEVELOPMENT: darcs get http://code.haskell.org/~basvandijk/code/threads CHANGES: * I removed the regular 'Control.Concurrent.ThreadId' out of our own 'ThreadId α' type and renamed the type to 'Result α': data ThreadId α = ThreadId { result ∷ TMVar (Either SomeException α) , threadId ∷ Control.Concurrent.ThreadId } to: newtype Result α = Result { unResult ∷ TMVar (Either SomeException α) } * The various fork functions now return the regular 'ThreadId' paired with a 'Result α' value: forkIO ∷ IO α → IO (ThreadId α) to: forkIO ∷ IO α → IO (ThreadId, Result α) * The various wait functions now just receive a 'Result α' value: wait ∷ ThreadId α → IO (Either SomeException α) to: wait ∷ Result α → IO (Either SomeException α) * I removed: throwTo ∷ Exception e ⇒ ThreadId α → e → IO () and: killThread ∷ ThreadId α → IO () because they aren't needed anymore since we have direct access to the regular 'ThreadId'. * When you build the package with GHC the GHC specific 'forkOnIO' function is additionally build in: forkOnIO ∷ Int → IO α → IO (ThreadId, Result α) * For the rest I added documentation and made some internal changes like a simplified implementation of ThreadGroups and made small stylistic changes all over the place. FUTURE PLANS: Inspired by the 'parIO' combinator from the 'async' package, I'm thinking about adding a module which offers similar functionality: data ParGroup α new ∷ IO (ParGroup α) forkIO ∷ ParGroup α → IO α → IO ThreadId wait ∷ ParGroup α → IO (Maybe α) The idea is that when you have multiple IO computations, that each compute the same answer but differ in how fast they compute that answer, you can compute them in parallel using 'forkIO'. Finally 'wait' blocks until one of the threads has computed an answer and will return Just that answer. When all of the threads fail to compute an answer (throw an exception) wait returns Nothing. Regards, Bas