#14106: Out of scope errors appear after type errors caused by them -------------------------------------+------------------------------------- Reporter: EyalLotem | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.2 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Poor/confusing | Unknown/Multiple error message | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Description changed by simonpj: Old description:

Example:

import Control.Lens (_Just, (&)) main = Just 5 & _Just .~ 100 & print

.~ is out of scope, the error output:

ghc-error.hs:2:17-21: error: … • Couldn't match type ‘Maybe’ with ‘p0 a0’ Expected type: Maybe (f0 b0) -> p0 (Maybe a0) (f0 (Maybe b0)) Actual type: p0 a0 (f0 b0) -> p0 (Maybe a0) (f0 (Maybe b0)) • In the second argument of ‘(&)’, namely ‘_Just’ In the first argument of ‘(.~)’, namely ‘Just 5 & _Just’ In the expression: (.~) Just 5 & _Just 100 & print ghc-error.hs:2:23-24: error: … • Variable not in scope: (.~) :: p0 (Maybe a0) (f0 (Maybe b0)) -> IO () -> t • Perhaps you meant ‘.’ (imported from Prelude) Perhaps you want to add ‘.~’ to the import list in the import of ‘Control.Lens’ (/home/eyal/devel/test/ghc-error.hs:1:1-32). Compilation failed.

In larger examples, the out of scope error can be buried deep down.

In the case of operators - the fixity is unknown so it can even cause the parse to go wrong - and very weird type errors to result from that.

Out of scope errors should be put BEFORE any type errors that might be caused by them.

New description: Example: {{{ import Control.Lens (_Just, (&)) main = Just 5 & _Just .~ 100 & print }}} .~ is out of scope, the error output: {{{ ghc-error.hs:2:17-21: error: … • Couldn't match type ‘Maybe’ with ‘p0 a0’ Expected type: Maybe (f0 b0) -> p0 (Maybe a0) (f0 (Maybe b0)) Actual type: p0 a0 (f0 b0) -> p0 (Maybe a0) (f0 (Maybe b0)) • In the second argument of ‘(&)’, namely ‘_Just’ In the first argument of ‘(.~)’, namely ‘Just 5 & _Just’ In the expression: (.~) Just 5 & _Just 100 & print ghc-error.hs:2:23-24: error: … • Variable not in scope: (.~) :: p0 (Maybe a0) (f0 (Maybe b0)) -> IO () -> t • Perhaps you meant ‘.’ (imported from Prelude) Perhaps you want to add ‘.~’ to the import list in the import of ‘Control.Lens’ (/home/eyal/devel/test/ghc-error.hs:1:1-32). Compilation failed. }}} In larger examples, the out of scope error can be buried deep down. In the case of operators - the fixity is unknown so it can even cause the parse to go wrong - and very weird type errors to result from that. Out of scope errors should be put BEFORE any type errors that might be caused by them. -- -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14106#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler