Hi
Put differently, I don't see a compelling use-case for the proposed syntax extension. But I've seen many misused monads.
A compelling use-case: http://darcs.haskell.org/yhc/src/libraries/core/Yhc/Core/Simplify.hs Look at coreSimplifyExprUniqueExt And from that file: -- helpers, ' is yes, _ is no coreCase__ x y = f $ CoreCase x y ; coreCase_' x y = f . CoreCase x =<< y coreLet__ x y = f $ CoreLet x y ; coreLet_' x y = f . CoreLet x =<< y coreLam__ x y = f $ CoreLam x y ; coreLam_' x y = f . CoreLam x =<< y coreApp__ x y = f $ CoreApp x y ; coreApp'_ x y = f . flip CoreApp y =<< x i.e. i've manually defined ' and _ variants to thread monadic effects through in quite horrible ways. The monad in question simply supplies free variables, so could be applied in any order. I think with this extension I can define: coreCase x y = f $ CoreCase x y coreLet x y = f $ CoreLet x y ... And taking just one rule, before: f (CoreApp (CoreLet bind xs) ys) = coreLet_' bind (coreApp__ xs ys) After: f (CoreApp (CoreLet bind xs) ys) = coreLet bind $(coreApp xs ys) Much nicer! This extension seems like a great idea - my only concern would be about the order of computations. Clearly left-to-right makes sense, but this may break some natural intuition in Haskell: flip f a b == f b a flip f $(a) $(b) /= f $(b) $(a) I don't think that is a show stopper though. Thanks Neil