Prune duplicates in ghci history

When we enter the same expressions in ghci, all of them go in to history. It'd be useful to have an option to eliminate duplicate expressions before storing them in ghci history.

We can also consider doing this for storing ghci history as a file.

Trac metadata

Trac field	Value
Version	6.8.3
Type	FeatureRequest
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	GHCi
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system	Unknown
Architecture	Unknown

changed weight to 5

added GHCi Tfeature request Trac import labels

changed milestone to %6.10 branch

Trac metadata

Trac field	Value
Architecture	Unknown → Unknown/Multiple

Trac metadata

Trac field	Value
Operating system	Unknown → Unknown/Multiple

changed milestone to %6.12 branch

changed milestone to %6.12.3

removed milestone

changed weight to 3

Trac metadata

Trac field	Value
Priority	normal → low

You can add the following line to your .haskeline file:

> historyDuplicates IgnoreConsecutive

or AlwaysAdd or IgnoreAll.

Right now the haskeline library reads all its preferences upon startup. The Prefs are in a ReaderT and so were presumably not designed to be updated during execution.

Trac metadata

Trac field	Value
TypeOfFailure	- → OtherFailure

changed milestone to %7.0.2

changed milestone to %7.2.1

changed milestone to %7.4.1

changed milestone to %7.6.1

changed weight to 0

Trac metadata

Trac field	Value
Priority	low → lowest

changed milestone to %7.6.2

changed milestone to %7.10.1

Moving to 7.10.1.