Accessing shadowed definitions in GHCi
Apparently GHCi creates a qualified namespace for each line it interprets, as can be observed with:
> data A = A
> data A = B
> :t A
A :: Ghci3.A
Apparently accessing shadowed definitions in this way sometimes breaks GHCi:
> let a = a
> let a = a
> :t Ghci7.a
<interactive>:1:1: error:
• GHC internal error: ‘Ghci7.a’ is not in scope during type checking, but it passed the renamer
tcl_env of environment: []
• In the expression: Ghci7.a
More specifically, complete reproduction instructions:
GHCi, version 8.1.20160205: http://www.haskell.org/ghc/ :? for help
> let foo = foo
> :t Ghci1.foo
Ghci1.foo :: t
> let foo = foo
> :t Ghci1.foo
<interactive>:1:1: error:
• GHC internal error: ‘Ghci1.foo’ is not in scope during type checking, but it passed the renamer
tcl_env of environment: []
• In the expression: Ghci1.foo
- 10.2 (and 7.8.3 as verified over IRC by monochrom) appears to have a slightly different behavior. It seems it only creates namespaces for data/newtype/class declarations. Yet still, it fails with an error the first time but works completely fine thereafter:
> data A = A
> data A = A
> :t Ghci1.A
Failed to load interface for ‘Ghci1’
no package key matching ‘interactive’ was found
> :t Ghci1.A
Ghci1.A :: Ghci1.A
- 6.3 uses a different approach to displaying out of scope names so the behavior doesn't apply:
> data A = A
> data A = B
> :t A
A :: main::Interactive.A
Trac metadata
Trac field | Value |
---|---|
Version | 8.0.1-rc1 |
Type | Bug |
TypeOfFailure | OtherFailure |
Priority | normal |
Resolution | Unresolved |
Component | GHCi |
Test case | |
Differential revisions | |
BlockedBy | |
Related | |
Blocking | |
CC | |
Operating system | |
Architecture |