let binding tuple of lenses error not an expression

This error seems to be fixed in GHC Head +/- 10 commits, but exists in GHC 8.0.1. I was told it might be a useful test case.

λ> :t userId
userId
  :: (RElem UserId rs (RIndex UserId rs), Functor f) =>
     (Int -> f Int) -> Record rs -> f (Record rs)
λ> let recLenses = userId &: Nil
λ> :t recLenses
recLenses
  :: (Functor f, RElem UserId rs (RIndex UserId rs)) =>
     Record '[s :-> ((Int -> f Int) -> Record rs -> f (Record rs))]
λ> :t recUncons
recUncons :: Record (s :-> a : rs) -> (a, Record rs)
λ> :t recUncons recLenses
recUncons recLenses
  :: (Functor f, RElem UserId rs (RIndex UserId rs)) =>
     ((Int -> f Int) -> Record rs -> f (Record rs), Record '[])
λ> let (l, ls) = recUncons recLenses

<no location info>: error:
    not an expression: ‘let (l, ls) = recUncons recLenses’

Trac metadata

Trac field	Value
Version	8.0.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	GHCi
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