#10188: prefix type-level cons can't be parsed -------------------------------------+------------------------------------- Reporter: Kinokkory | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.4 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects | Unknown/Multiple valid program | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Revisions: -------------------------------------+------------------------------------- Comment (by simonpj): Good point. This is just a question of fixing the parser. Would anyone like to have a go? Simon -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10188#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#10188: prefix type-level cons can't be parsed -------------------------------------+------------------------------------- Reporter: Kinokkory | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.4 (Parser) | Keywords: Resolution: | Architecture: Operating System: Unknown/Multiple | Unknown/Multiple Type of failure: GHC rejects | Test Case: valid program | Blocking: Blocked By: | Differential Revisions: Related Tickets: | -------------------------------------+------------------------------------- Description changed by Kinokkory: Old description:

Whereas other type operators (whether used as type families or used as data constructors) can be safely used in a prefix form, only the type- level cons of the built-in list kind can't be used in a prefix form.

It really is a problem because we don't have any means to express type- level cons itself in source code. This for example prevents us from writing a generic type-level foldr that takes the built-in list and other similar data types alike.

In a ghci:

{{{#!hs

...

:set -XDataKinds -XTypeOperators data Listy a = a ::: Listy a :kind! (:::) (:::) :: k -> Listy k -> Listy k = forall (k :: BOX). (':::) :kind! (:)

<interactive>:1:2: parse error on input ‘:’ }}}

New description: Whereas other type operators (whether used as type families or used as data constructors) can be safely used in a prefix form, only the type- level cons of the built-in list kind can't be used in a prefix form. It really is a problem because we don't have any means to express the type-level cons itself in source code. This for example prevents us from writing a generic type-level foldr that takes the built-in list and other similar data types alike. In a ghci: {{{#!hs

:set -XDataKinds -XTypeOperators data Listy a = a ::: Listy a | Nily :kind! (:::) (:::) :: k -> Listy k -> Listy k = forall (k :: BOX). (':::) :kind! (:)

<interactive>:1:2: parse error on input ‘:’ }}} -- -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10188#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#10188: prefix type-level cons can't be parsed -------------------------------------+------------------------------------- Reporter: Kinokkory | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.4 (Parser) | Keywords: Resolution: | Architecture: Operating System: Unknown/Multiple | Unknown/Multiple Type of failure: GHC rejects | Test Case: valid program | Blocking: Blocked By: | Differential Revisions: Related Tickets: | -------------------------------------+------------------------------------- Comment (by Kinokkory): Oh, I didn't know that. Thanks a lot! In a ghci: {{{#!hs

:kind! '(:::) '(:::) :: k -> Listy k -> Listy k = forall (k :: BOX). (':::) :kind! (':::)

<interactive>:1:3: parse error on input ‘:::’

:kind! (':)

<interactive>:1:3: parse error on input ‘:’ }}} The message "forall (k :: BOX). (':::)" seems inconsistent with the parsing mechanism that allows "'(:::)" instead of (':::). I'll report this as another new bug! -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10188#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#10188: prefix type-level cons can't be parsed -------------------------------------+------------------------------------- Reporter: Kinokkory | Owner: Kinokkory Type: bug | Status: new Priority: normal | Milestone: 7.12.1 Component: Compiler | Version: 7.8.4 (Parser) | Keywords: Resolution: | Architecture: Operating System: Unknown/Multiple | Unknown/Multiple Type of failure: GHC rejects | Test Case: valid program | Blocking: Blocked By: | Differential Revisions: Related Tickets: #10189 | -------------------------------------+------------------------------------- Changes (by Kinokkory): * cc: Kinokkory (added) * owner: => Kinokkory * milestone: => 7.12.1 -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10188#comment:7 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#10188: prefix type-level cons can't be parsed -------------------------------------+------------------------------------- Reporter: Kinokkory | Owner: Kinokkory Type: bug | Status: patch Priority: normal | Milestone: 7.12.1 Component: Compiler | Version: 7.8.4 (Parser) | Keywords: Resolution: | Architecture: Operating System: Unknown/Multiple | Unknown/Multiple Type of failure: GHC rejects | Test Case: valid program | Blocking: Blocked By: | Differential Revisions: Phab:D768 Related Tickets: #10189 | -------------------------------------+------------------------------------- Comment (by Kinokkory): This patch makes `(:) Int [Float, Double]` and `Int : [Float, Double]` parsed. In fact, infix type-level cons also used to be not parsed without `'`. Essentially, I changed the definition of `tyconsym` by adding `| ':' ...`. {{{ tyconsym :: { Located RdrName } : CONSYM { sL1 $1 $! mkUnqual tcClsName (getCONSYM $1) } | VARSYM { sL1 $1 $! mkUnqual tcClsName (getVARSYM $1) } | ':' { sL1 $1 $! consDataCon_RDR } | '*' { sL1 $1 $! mkUnqual tcClsName (fsLit "*") } | '-' { sL1 $1 $! mkUnqual tcClsName (fsLit "-") } }}} By the way I wonder what `| '*' ...` and `| '-' ...` are for. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10188#comment:9 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#10188: prefix type-level cons can't be parsed -------------------------------------+------------------------------------- Reporter: Kinokkory | Owner: Kinokkory Type: bug | Status: patch Priority: normal | Milestone: 7.12.1 Component: Compiler | Version: 7.8.4 (Parser) | Keywords: Resolution: | Architecture: Operating System: Unknown/Multiple | Unknown/Multiple Type of failure: GHC rejects | Test Case: valid program | Blocking: Blocked By: | Differential Revisions: Phab:D768 Related Tickets: #10189 | -------------------------------------+------------------------------------- Comment (by Austin Seipp ): In [changeset:"012ea0b96cc041bced4565d74bef7ccb75f1af0d/ghc"]: {{{ #!CommitTicketReference repository="ghc" revision="012ea0b96cc041bced4565d74bef7ccb75f1af0d" parser: allow type-level cons in prefix position Reviewed By: austin Differential Revision: https://phabricator.haskell.org/D768 GHC Trac Issues: #10188 }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10188#comment:11 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler