#13602: Pattern syntax in expression context must be clarified -------------------------------------+------------------------------------- Reporter: vanto | Owner: (none) Type: feature | Status: new request | Priority: normal | Milestone: Component: Compiler | Version: 8.0.2 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Incorrect Unknown/Multiple | error/warning at compile-time Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- To simonpj\\ see tickets {{{#13557}}} and {{{#13579}}}\\ Typed Holes does not exist if we compile with GHC version 7.6.3. Instead of "error found holes" it indicates "pattern syntax in expression context: _".\\ I then understood that to improve Typed Holes it was first necessary to remove the ambiguity of the error in GHC 7.6.3 about pattern syntax in expression.\\ {{{let f = [True | x <- [_, _]]}}} raise the error {{{pattern syntax in expression context: _}}}\\ But as Typed Holes, this error has no sense here.\\ {{{let f' = [_ | x <- [1,2]]}}}will give a result like {{{"__"}}} And this calculation also makes sense if one refers to the rule of inference, as the function {{{f}}} .\\ \\ The compiler should not impose its way.\\ The programmer must be the master of his code. Here the rule of inference seems flouted.\\ Good sense or reason is argued to be the same in all people, yet differences in opinion are not due to differences in intelligence but to the fact that we use different approaches and consider different things.\\ Here you will find some ideas:\\ Instead of "underscore _" as "pattern syntax" we could use a new type called "indefinite" in expression.\\ Any calculation with "indefinite" will result in "indefinite".\\ In another calculation, the "indefinite" type could have a type defined according to a directive applied to the compiler.\\ example:\\ indefinite :: Int\\ f = [1,2,3,indefinite,5,6]\\ I took a look at ticket {{{#9497}}} and find it very interesting.\\ -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13602 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler