#8815: confusing language in error message ------------------------------------+------------------------------------- Reporter: carter | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.1-rc1 Keywords: | Operating System: Unknown/Multiple Architecture: Unknown/Multiple | Type of failure: None/Unknown Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | ------------------------------------+------------------------------------- Late last night I was finding myself very confused by the following (in retrospect obvious error message) {{{ src/Numerical/OpenBLAS/BLAS.hs:41:44: A pattern match on a GADT requires GADTs or TypeFamilies In the pattern: SRow In the pattern: DenseMatrix SRow _ _ _ _ In an equation for ‛encodeNiceOrderHelper’: encodeNiceOrderHelper (DenseMatrix SRow _ _ _ _) = encodeOrder BLASRowMajor }}} the error is correct per se, but reading (at least late at night) made me think "wait, how is my type not a GADT or TypeFamily?!!?!" I'm thinking (perhaps ) that ``` A pattern match on a GADT requires GADTs or TypeFamilies `` ` could perhaps be more clearly communicated as ```A pattern match on a GADT requires that GADTs or TypeFamilies Language extensions be enabled in the use site module``` (or something similar) relatedly: whats the current reasoning for why GADT related matching logic isn't enabled in client modules that use GADTs? (i'm not questioning it, just wondering why) -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8815 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler