Wacky error message when RULE mentions out-of-scope variable
If I compile the following program with GHC 8.4 or later:
module Foo where
{-# RULES "test" forall x. f x = x #-}
The error message I get is somewhat eyebrow-raising:
$ /opt/ghc/8.4.3/bin/ghc Foo.hs
[1 of 1] Compiling Foo ( Foo.hs, Foo.o )
Foo.hs:3:11: error:
Rule "test":
Not in scope: OutOfScope(f)
in left-hand side: f x
LHS must be of form (f e1 .. en) where f is not forall'd
|
3 | {-# RULES "test" forall x. f x = x #-}
| ^^^^^^^^^^^^^^^^^^^^^^^^
I'm not sure what this OutOfScope
business is, but I doubt we want to be referring to it in error messages. The error in GHC 8.2 and earlier was much less confusing:
$ /opt/ghc/8.2.2/bin/ghc Foo.hs
[1 of 1] Compiling Foo ( Foo.hs, Foo.o )
Foo.hs:3:11: error:
Rule "test":
Not in scope: f
in left-hand side: f x
LHS must be of form (f e1 .. en) where f is not forall'd
|
3 | {-# RULES "test" forall x. f x = x #-}
| ^^^^^^^^^^^^^^^^^^^^^^^^
Trac metadata
Trac field | Value |
---|---|
Version | 8.4.3 |
Type | Bug |
TypeOfFailure | OtherFailure |
Priority | normal |
Resolution | Unresolved |
Component | Compiler |
Test case | |
Differential revisions | |
BlockedBy | |
Related | |
Blocking | |
CC | |
Operating system | |
Architecture |