#12188: Pattern variables bound by PatternGuards are not accessible in where clause -------------------------------------+------------------------------------- Reporter: heisenbug | Owner: Type: bug | Status: closed Priority: normal | Milestone: Component: Compiler | Version: 7.10.3 Resolution: invalid | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects | Unknown/Multiple valid program | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj): Richard is right. In Haskell * The patterns of the function definition scope over guards, where clause, and body * The where clause scopes over the guards, and body. * The guards scope over the body only Once could define the language differently, but that's the way it is in Haskell. You can include let-binding in the guards, if you want: {{{ foo :: Int -> Bool foo a | Just b <- return a , let c = a == b = c }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12188#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler