On 11/02/15 04:39 AM, Simon Peyton Jones wrote:

($) has its own *typing rule*; it does not have a special type. It's very ad hoc, but ($) is used so much to decrease parens that (e1 $ e2) is almost special syntax!

I do like the idea of being able to end a function application with a lambda, let, if, case, or do without having to use $ though. Would something like the following grammar rules be problematic for parsing? infixexp→ lexp qop infixexp | - infixexp | [fexp] lexp (*) | aexp (*) lexp → \ apat1 … apatn -> exp | let decls in exp | if exp [;] then exp [;] else exp | case exp of { alts } | do { stmts } (*) fexp → [fexp] aexp aexp → qvar | gcon | literal | ( exp ) | ( exp1 , … , expk ) | [ exp1 , … , expk ] | [ exp1 [, exp2] .. [exp3] ] | [ exp | qual1 , … , qualn ] | ( infixexp qop ) | ( qop⟨-⟩ infixexp ) | qcon { fbind1 , … , fbindn } | aexp⟨qcon⟩ { fbind1 , … , fbindn } https://www.haskell.org/onlinereport/haskell2010/haskellch3.html were I've added (*) to where I have added or removed lines (basically I've moved function application from lexp to infixexp in order to allow the last exp in a function application to be an lexp).

At the moment the *only* robust way to pass a polymorphic function to a polymorphic function (here, you are passing Wrap to (.)) is to wrap it in a newtype, much as Wrap does.

Good to know. Thanks! -Tyson