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Why can't I do this?

{-# LANGUAGE TypeApplications #-}
module Bug where

foo :: [Int]
foo = [] @Int

Compiling this with GHC 8.0.1, 8.0.2, 8.2.1, or HEAD gives me:

$ /opt/ghc/head/bin/ghci Bug2.hs
GHCi, version 8.3.20170509: http://www.haskell.org/ghc/  :? for help
Loaded GHCi configuration from /home/rgscott/.ghci
[1 of 1] Compiling Bug              ( Bug2.hs, interpreted )

Bug2.hs:5:7: error:
    • Cannot apply expression of type ‘[a0]’
      to a visible type argument ‘Int’
    • In the expression: [] @Int
      In an equation for ‘foo’: foo = [] @Int
  |
5 | foo = [] @Int
  |       ^^^^^^^

This seems really strange, since I can use TypeApplications with expressions like Nothing @Int without issues. According to GHCi:

$ /opt/ghc/head/bin/ghci
GHCi, version 8.3.20170509: http://www.haskell.org/ghc/  :? for help
Loaded GHCi configuration from /home/rgscott/.ghci
λ> :set -XTypeApplications -fprint-explicit-foralls 
λ> :type +v []
[] :: forall {a}. [a]
λ> :type +v Nothing
Nothing :: forall a. Maybe a

The type variable for [] isn't visible! But I don't see any reason why it shouldn't be, especially since, conceptually, the data type declaration for lists is:

data [] a = [] | a : [a]

I suspect that []'s tyvar binder visibility is not wired into GHC correctly.

Trac metadata

Trac field	Value
Version	8.0.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler (Type checker)
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