Futures in Haskell

Question

Does Haskell have an equivalent of Alice's ability to bind a variable to a future?

val a = spawn foo;

where foo is some function.

I know Haskell supports channels and threads; I'm hoping for syntax as natural as Alice's to bind a value to a future and spawn a thread to calculate it without having to deal with the details.

Jurat

Unrelated, but Clojure actually has those as well. – Monseigneur

I've never looked into this myself, but I suspect that lazy IO can be made to do this in a really neat way, although it may have unsafeInterleaveIO under the hood. – Wiseacre

Answer 1

You can use par from Control.Parallel as in

a `par` f a b c
where
  a = foo

This is a hint to the runtime that a could be evaluated in another thread.

Rhinoscopy

Answer 2

Funny, I was just reading a new post by Simon Marlow: Parallel programming in Haskell with explicit futures. Apparently he and others have been working on some new parallel programming abstractions that are intended to be more natural and explicit than the par and pseq APIs.

Belk

Answer 3

Not in the standard library, but

http://ghcmutterings.wordpress.com/2010/08/20/parallel-programming-in-haskell-with-explicit-futures/

data Future a = Future a

fork :: Eval a -> Eval (Future a)
fork a = do a' <- rpar (runEval a); return (Future a')

join :: Future a -> Eval a
join (Future a) = a `pseq` return a

Sternick

"parallel" is part of the Haskell Platform, and regular lazy futures (par ) are already part of it. – Konyn

Why isn't this Future api in the standard library? This is much easier for me to reason about than par and co. – Defection