"ghci -XMonomorphismRestriction" doesn't turn on the monomorphism restriction

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rwbarton@morphism:/tmp$ ghci-7.10.1 -XMonomorphismRestriction
GHCi, version 7.10.1: http://www.haskell.org/ghc/  :? for help
Prelude> let a = (+)
Prelude> :t a
a :: Num a => a -> a -> a

with

rwbarton@morphism:/tmp$ ghci-7.10.1 
GHCi, version 7.10.1: http://www.haskell.org/ghc/  :? for help
Prelude> :set -XMonomorphismRestriction
Prelude> let a = (+)
Prelude> :t a
a :: Integer -> Integer -> Integer

Confusing!

This also occurred in 7.8.

Trac metadata

Trac field	Value
Version	7.10.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	GHCi
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