#13506: Spurious extra error message due to functional dependencies -------------------------------------+------------------------------------- Reporter: gelisam | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler (Type | Version: 8.0.2 checker) | Resolution: | 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: | -------------------------------------+------------------------------------- Comment (by RyanGlScott): This error message has had an interesting history. In GHC 7.4.2 and earlier, you get the error message that you desire: {{{ GHCi, version 7.4.2: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... linking ... done. [1 of 1] Compiling Bug ( Bug.hs, interpreted ) Bug.hs:16:12: Couldn't match type `Char' with `()' When using functional dependencies to combine FunDep [a] a, arising from the dependency `lista -> a' in the instance declaration at Bug.hs:5:10 FunDep [Char] (), arising from a use of `singleton' at Bug.hs:16:12-20 In the expression: singleton () In an equation for `illTyped': illTyped = singleton () Failed, modules loaded: none. }}} In GHC 7.6.3, it changed to the current behavior: {{{ GHCi, version 7.6.3: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... linking ... done. [1 of 1] Compiling Bug ( Bug.hs, interpreted ) Bug.hs:16:12: Couldn't match type `Char' with `()' When using functional dependencies to combine FunDep [a] a, arising from the dependency `lista -> a' in the instance declaration at Bug.hs:5:10 FunDep [Char] (), arising from a use of `singleton' at Bug.hs:16:12-20 In the expression: singleton () In an equation for `illTyped': illTyped = singleton () Bug.hs:24:13: Couldn't match type `()' with `Char' When using functional dependencies to combine FunDep [Char] (), arising from a use of `singleton' at Bug.hs:16:12-20 FunDep [Char] Char, arising from a use of `singleton' at Bug.hs:24:13-21 In the expression: singleton 'a' In an equation for `wellTyped': wellTyped = singleton 'a' }}} But in GHC 7.8.4, it was briefly fixed again! {{{ GHCi, version 7.8.4: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... linking ... done. [1 of 1] Compiling Bug ( Bug.hs, interpreted ) Bug.hs:16:12: No instance for (FunDep [Char] ()) arising from a use of ‘singleton’ In the expression: singleton () In an equation for ‘illTyped’: illTyped = singleton () }}} But in GHC 7.10.3 and later, we get the current error message again. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13506#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#13506: Spurious extra error message due to functional dependencies -------------------------------------+------------------------------------- Reporter: gelisam | Owner: (none) Type: bug | Status: closed Priority: normal | Milestone: Component: Compiler (Type | Version: 8.0.2 checker) | Resolution: fixed | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: Incorrect | Test Case: error/warning at compile-time | typecheck/should_fail/T13506 Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by simonpj): * testcase: => typecheck/should_fail/T13506 * status: new => closed * resolution: => fixed Comment: Excellent test case, thank you. Fixed! Simon -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13506#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler