#13420: Bizarre pretty-printing of closed type families in GHCi -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: GHCi | Version: 8.0.2 Keywords: TypeFamilies | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Load this code: {{{#!hs {-# LANGUAGE TypeFamilies #-} module Bug where type family F a where F [Int] = Bool F [a] = Double F (a b) = Char }}} into GHCi 8.0.1, 8.0.2, or HEAD, and run `:i F`. You'll see this: {{{ $ /opt/ghc/8.0.2/bin/ghci Bug.hs GHCi, version 8.0.2: http://www.haskell.org/ghc/ :? for help Loaded GHCi configuration from /home/rgscott/.ghci [1 of 1] Compiling Bug ( Bug.hs, interpreted ) Ok, modules loaded: Bug. λ> :i F type family F a :: * where F [Int] = Bool [a] F [a] = Double [b, (a :: * -> *)] F (a b) = Char -- Defined at Bug.hs:4:1 }}} Compare this with GHCi 7.10.3, where the pretty-printing is far more sane: {{{ $ /opt/ghc/7.10.3/bin/ghci Bug.hs GHCi, version 7.10.3: http://www.haskell.org/ghc/ :? for help [1 of 1] Compiling Bug ( Bug.hs, interpreted ) Ok, modules loaded: Bug. λ> :i F type family F a :: * where F [Int] = Bool F [a] = Double F (a b) = Char -- Defined at Bug.hs:4:1 }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13420 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler