On Wed, May 14, 2008 at 03:59:23PM +0100, Edsko de Vries wrote:
You mention that a "direct" implementation of what I suggested would break the monad laws, as (foo) and (Let foo id) are not equal. But one might argue that they are in fact, in a sense, equivalent. Do you reckon that if it is acceptable that foo and do { a <- foo; return a } don't return equal terms (but equivalent terms), we can do still better?
If you just want the syntactic sugar and don't care about monads, in GHC you can use plain do-notation: {-# OPTIONS -fno-implicit-prelude #-} import Prelude hiding ((>>=), fail) data Expr = One | Add Expr Expr | Let Expr (Expr -> Expr) (>>=) = Let fail = error t :: Expr t = do a <- One b <- Add a a Add b b That's generally pretty icky, though. Lauri