#14343: bad pretty-printing of types with promoted data types -------------------------------------+------------------------------------- Reporter: lspitzner | Owner: (none) Type: bug | 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 simonpj): Are you sure you put that in right? With GHC 8.2.1 I get {{{ Prelude> _ :: Proxy '[ 'True ] <interactive>:3:1: error: • Found hole: _ :: Proxy '['True] • In the expression: _ :: Proxy '[ 'True] In an equation for ‘it’: it = _ :: Proxy '[ 'True] • Relevant bindings include it :: Proxy '['True] (bound at <interactive>:3:1) }}} But if I miss out the space it parses `'['` as a character literal. {{{ Prelude> _ :: Proxy '['True ] <interactive>:4:1: error: Invalid type signature: _ :: ... Should be of form <variable> :: <type> }}} Hard to avoid that. Make sense? I'm inclined to say 'wont-fix'. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14343#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#14343: bad pretty-printing of types with promoted data types -------------------------------------+------------------------------------- Reporter: lspitzner | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1 Resolution: | Keywords: newcomer Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by RyanGlScott): * keywords: => newcomer Comment: This is just a deficiency of GHC's pretty-printer. It should be relatively straightforward to change it such that GHC inserts a space between `'[` and `'True`. See the [http://git.haskell.org/ghc.git/blob/6a9b9b431dcc94849d14c13639eb2f713e5aa1f4... pprIfaceTyList] function, which is responsible for pretty-printing promoted lists. Note that similar considerations also apply for promoted tuple constructors: {{{ λ> f :: Proxy _ -> Proxy '( 'True, 'True); f x = x <interactive>:5:12: error: • Found type wildcard ‘_’ standing for ‘'('True, 'True) :: (Bool, Bool)’ To use the inferred type, enable PartialTypeSignatures • In the type signature: f :: Proxy _ -> Proxy '( 'True, 'True) }}} So an analogous fix would be needed for the [http://git.haskell.org/ghc.git/blob/6a9b9b431dcc94849d14c13639eb2f713e5aa1f4... pprTuple] function. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14343#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#14343: bad pretty-printing of types with promoted data types -------------------------------------+------------------------------------- Reporter: lspitzner | Owner: andreash Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1 Resolution: | Keywords: newcomer Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D4746 Wiki Page: | -------------------------------------+------------------------------------- Changes (by RyanGlScott): * differential: => Phab:D4746 -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14343#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#14343: bad pretty-printing of types with promoted data types -------------------------------------+------------------------------------- Reporter: lspitzner | Owner: andreash Type: bug | Status: patch Priority: normal | Milestone: Component: Compiler | Version: 8.2.1 Resolution: | Keywords: newcomer Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D4746 Wiki Page: | -------------------------------------+------------------------------------- Comment (by Ben Gamari ): In [changeset:"767536ccf95d8352d146b6544857b28d9c42937e/ghc" 767536c/ghc]: {{{ #!CommitTicketReference repository="ghc" revision="767536ccf95d8352d146b6544857b28d9c42937e" Fix unparseable pretty-printing of promoted data cons Previously we would print code which would not round-trip: ```

:set -XDataKinds :set -XPolyKinds data Proxy k = Proxy _ :: Proxy '[ 'True ] error: Found hole: _ :: Proxy '['True] _ :: Proxy '['True] error: Invalid type signature: _ :: ... Should be of form <variable> :: <type>

Test Plan: Validate with T14343

Reviewers: RyanGlScott, goldfire, bgamari, tdammers

Reviewed By: RyanGlScott, bgamari

Subscribers: tdammers, rwbarton, thomie, carter

GHC Trac Issues: #14343

Differential Revision: https://phabricator.haskell.org/D4746
}}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14343#comment:7>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler

#14343: bad pretty-printing of types with promoted data types -------------------------------------+------------------------------------- Reporter: lspitzner | Owner: andreash Type: bug | Status: closed Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.2.1 Resolution: fixed | Keywords: newcomer Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D4746 Wiki Page: | -------------------------------------+------------------------------------- Comment (by Simon Peyton Jones ): In [changeset:"ae2c9b40f5b6bf272251d1f4107c60003f541b62/ghc" ae2c9b40/ghc]: {{{ #!CommitTicketReference repository="ghc" revision="ae2c9b40f5b6bf272251d1f4107c60003f541b62" Smarter HsType pretty-print for promoted datacons Fix Trac #15898, by being smarter about when to print a space before a promoted data constructor, in a HsType. I had to implement a mildly tiresome function HsType.lhsTypeHasLeadingPromotionQuote It has multiple cases, of course, but it's very simple. The patch improves the error-message output in a bunch of cases, and (to my surprise) actually fixes a bug in the output of T14343 (Trac #14343), thus - In the expression: _ :: Proxy '('( 'True, 'False), 'False) + In the expression: _ :: Proxy '( '( 'True, 'False), 'False) I discovered that there were two copies of the PromotionFlag type (a boolean, with helpfully named data cons), one in IfaceType and one in HsType. So I combined into one, PromotionFlag, and moved it to BasicTypes. That's why quite a few files are touched, but it's all routine. }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14343#comment:9 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler