#15767: "StgCmmEnv: variable not found" with FunctionalDependencies and FlexibleContexts -------------------------------------+------------------------------------- Reporter: roland | Owner: (none) Type: bug | Status: merge Priority: normal | Milestone: Component: Compiler | Version: 8.6.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: Compile-time | Test Case: crash or panic | typecheck/should_fail/T15767 Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by bgamari): I'm afraid I'm seeing some spurious test output changes when cherry- picking this to `ghc-8.6`. For instance, {{{#!patch diff -uw "./rename/should_fail/mc13.run/mc13.stderr.normalised" "./rename/should_fail/mc13.run/mc13.comp.stderr.normalised" --- ./rename/should_fail/mc13.run/mc13.stderr.normalised 2018-10-30 14:54:22.690690790 -0400 +++ ./rename/should_fail/mc13.run/mc13.comp.stderr.normalised 2018-10-30 14:54:22.690690790 -0400 @@ -1,2 +1,18 @@ -mc13.hs:12:37: Variable not in scope: f :: [a] -> m a +mc13.hs:12:16: + Ambiguous type variable ‘m0’ arising from a statement in a monad comprehension + prevents the constraint ‘(Monad m0)’ from being solved. + Relevant bindings include output :: m0 () (bound at mc13.hs:12:1) + Probable fix: use a type annotation to specify what ‘m0’ should be. + These potential instances exist: + instance Monad IO -- Defined in ‘GHC.Base’ + instance Monad Maybe -- Defined in ‘GHC.Base’ + instance Monoid a => Monad ((,) a) -- Defined in ‘GHC.Base’ + ...plus one other + ...plus two instances involving out-of-scope types + (use -fprint-potential-instances to see them all) + In a stmt of a monad comprehension: then f + In the expression: [() | f <- functions, then f] + In an equation for ‘output’: output = [() | f <- functions, then f] + +mc13.hs:12:37: Variable not in scope: f :: [a] -> m0 a }}} and similar new errors in `TEST="T12529 T12921 mc13 mc14"`. Given that these are just error message regressions I'm going to go ahead and accept them (and perhaps we can fix them later if anyone knows the cause off- hand). -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15767#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler