#15898: Promoted type constructors don't print right in HsType -------------------------------------+------------------------------------- Reporter: simonpj | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.6.3 Component: Compiler | Version: 8.6.2 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Consider this {{{ ghci> import Data.Proxy ghci> undefined :: '() -> Int <interactive>:11:14: error: • Expected a type, but ‘ '()’ has kind ‘()’ • In an expression type signature: '() -> Int }}} What is that strange space doing before the `'()`? Similarly {{{ undefined :: Proxy '() Int <interactive>:12:14: error: • Expected kind ‘* -> *’, but ‘Proxy '()’ has kind ‘*’ • In an expression type signature: Proxy '() Int }}} Again, the strange space. It comes from the `HsType` pretty printer, which is worried about printing the type {{{ '['K] }}} That is, a promoted list with one element `K`. The trouble is that looks like a character literal `'['`. So we add an extra space, thus `'[ 'K]`. ''But we add it before every promoded data constructor!" Hence the spurious spaces. In `IfaceType` exactly the same thing happens, but we are more clever, and only print the leading space if the promoted data con immediately follows `'[` or `'(`. We should do the same thing for `HsType`. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15898 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler