#14646: GHC 8.4.1 regression: rank-n types no longer parenthesized when pretty- printed -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: high | Milestone: 8.4.1 Component: GHC API | Version: 8.4.1-alpha1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Incorrect result Unknown/Multiple | at runtime Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Take this file: {{{#!hs {-# LANGUAGE RankNTypes #-} {-# LANGUAGE TemplateHaskell #-} {-# OPTIONS_GHC -ddump-splices #-} module Bug where import Language.Haskell.TH $([d| f :: (forall a. a) -> Int f _ = undefined |]) }}} In GHC 8.2.2, `-ddump-splices` behaves as you'd expect: {{{ $ /opt/ghc/8.2.2/bin/ghci Bug.hs GHCi, version 8.2.2: http://www.haskell.org/ghc/ :? for help Loaded GHCi configuration from /home/rgscott/.ghci [1 of 1] Compiling Bug ( Bug.hs, interpreted ) Bug.hs:(8,3)-(9,24): Splicing declarations [d| f_a1zL :: (forall a_a1zM. a_a1zM) -> Int f_a1zL _ = undefined |] ======> f_a49Z :: (forall a_a4a0. a_a4a0) -> Int f_a49Z _ = undefined Ok, one module loaded. }}} But in GHC 8.4.1-alpha (and HEAD), the GHC pretty-printer incorrectly leaves off the parentheses around the type `(forall a. a)`: {{{ $ /opt/ghc/8.4.1/bin/ghci Bug.hs GHCi, version 8.4.0.20171222: http://www.haskell.org/ghc/ :? for help Loaded GHCi configuration from /home/rgscott/.ghci [1 of 1] Compiling Bug ( Bug.hs, interpreted ) Bug.hs:(8,3)-(9,24): Splicing declarations [d| f_a1EF :: (forall a_a1EG. a_a1EG) -> Int f_a1EF _ = undefined |] ======> f_a4ap :: forall a_a4aq. a_a4aq -> Int f_a4ap _ = undefined Ok, one module loaded. }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14646 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler