#8387: View patterns + pattern bindings: finnicky about scoping ----------------------------------------------+---------------------------- Reporter: tinctorius | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.6.3 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects valid program | Unknown/Multiple Test Case: | Difficulty: Unknown Blocking: | Blocked By: | Related Tickets: ----------------------------------------------+---------------------------- Comment (by rwbarton): It is related to #4061, and I think that GHC is correctly implementing the scoping rule in the user's guide:
In mutually recursive bindings, such as let, where, or the top level, view patterns in one declaration may not mention variables bound by other declarations. That is, each declaration must be self-contained.
That doesn't mean the rule is written in stone. I wonder whether it could be:
In mutually recursive bindings ... view patterns in one declaration may not mention variables bound by other ''view patterns''.
---- As a workaround, you can use the Template Haskell hack I just posted on #4061 to get your second example to compile. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8387#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler