#3306: Improve syntax for GADT + records -------------------------------------+------------------------------------- Reporter: simonpj | Owner: simonpj Type: feature request | Status: closed Priority: normal | Milestone: 6.12.1 Component: Compiler | Version: 6.10.2 Resolution: fixed | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Revisions: -------------------------------------+------------------------------------- Changes (by skvadrik): * failure: => None/Unknown Comment: 6 years later: removed deprecated syntax for GADT constuctors. This allows to get rid of 2 reduce/reduce conflicts in parser. Conflicting productions were: {{{ gadt_constr -> con_list '::' sigtype gadt_constr -> oqtycon '{' fielddecls '}' '::' sigtype }}} Recursive inlining of con_list and oqtycon helped reveal the conflict: {{{ gadt_constr -> '(' CONSYM ')' '::' sigtype gadt_constr -> '(' CONSYM ')' '{' fielddecls '}' '::' sigtype }}} between two types of GADT constructors (second form stands for deprecated syntax). However, old syntax allowed `oqtycon` in constructor names, while new syntax allows `con` (which is not the same). There are therefore some constructor names that cannot be expressed in terms of new syntax (e.g. `(*)`). Note that ordinary data constructors are parsed in a different way than GADTs: types and names are mixed, so names have to be parsed as types and then converted to names. In GADTs constructor names and types are separated by `::`, so names can be parsed as just names and not as types. This results in a difference in the set of names allowed in GADT and ordinary constructors. See `Note [Parsing data constructors is hard]` and `Note [Difference in parsing GADT and data constructors]` Differential Revision: https://phabricator.haskell.org/D1118 -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/3306#comment:8 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler