#14088: Allow users to omit `forall` -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: (none) Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by RyanGlScott): I don't support this idea. The issue is that in a type signature like `forall a b. a b`, there are two different varieties of type variables. There are type variable //binders// which appear between the `forall` and the dot (e.g., the `a` and `b` in `forall a b.`), and type variable //types//, which occur to right of the dot (e.g., the `a` and `b` in `. a b`). Syntactically, however, the difference between these two is not always so clear. This is where the `forall` keyword is extremely helpful to the reader. It gives a clear indication that what follows are type variable binders and not proper types. If we allow `forall` to be omitted, however, mentally parsing type signatures will become more of a chore. For instance, if you have this type signature: {{{#!hs f :: a b c d e f g h i j k l m n o p q r s t u v w x y z aa bb cc dd ee ff gg hh ii jj kk ll mm nn oo pp qq rr ss tt uu vv ww xx yy zz. a b c d e f g h i j k l m n o p q r s t u v w x y z aa bb cc dd ee ff gg hh ii jj kk ll mm nn oo pp qq rr ss tt uu vv ww xx yy zz }}} When I start reading the type of `f`, I have no idea if I'm looking at binders or types. I have to reserve extra lookahead to figure out what I'm looking at. With `forall`, this isn't an issue, because I can know instantly where the binders start. I'm not even sure what omitting `forall` even buys you. As AntC says, if you wish to write terser code, this is a perfectly cromulent thing to do: {{{ {-# LANGUAGE RankNTypes #-} {-# LANGUAGE UnicodeSyntax #-} id :: ∀ a. a -> a id x = x }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14088#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler