Where-clause environments for GHCi

Often in ghci I'd like to interactively debug and play with functions in the where clause of a top-level definition. Currently, this requires one to change the code, lifting the definitions in question to the top level and adding appropriate parameters.

Given a definition such as

top :: Int -> Int
top x = mult 4 - mult 3 + mult 2
    where
        mult n = x * n

it would be nice to type something such as :environment top 2 to put me in an envrionment where mult is available and mult 4 will evaluate to 8. (Obviously this becomes more useful with more complex definitions.)

Trac metadata

Trac field	Value
Version	6.10.3
Type	FeatureRequest
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	GHCi
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