#15851: Error message: "accepting non-standard pattern guards" when there are no actual patterns -------------------------------------+------------------------------------- Reporter: cdsmith | Owner: (none) Type: feature | Status: new request | Priority: normal | Milestone: Component: Compiler | Version: 8.6.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- This code: {{{#!hs {-# LANGUAGE NoPatternGuards #-} main :: IO () main = print (foo 5) foo :: Int -> Int foo x | x < 5, x > 1 = x | otherwise = -1 }}} Produces this message: {{{ test.hs:7:7: warning: accepting non-standard pattern guards (use PatternGuards to suppress this message) x < 5, x > 1 }}} This is not really a "pattern guard". It's just a guard with multiple clauses, which is a syntax extension that's enabled by `-XPatternGuards`, but there are no patterns. (Incidentally, I wish I could disable pattern guards to avoid the `f x |x<-4` problem where a student tries to compare to negative 4 and gets an accidental pattern guard, yet still keep the multiple-clause syntax; but that's a whole different can of worms.) -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15851 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler