Add fromLeft and fromRight to Data.Either

This ticket is the result of the discussion of the proposal on the libraries mailing list to add the following two functions to Data.Either in base:

fromLeft :: a -> Either a b -> a
fromRight :: b -> Either a b -> b

The functions extract an Either a b value for the constructors in their namesake, providing their first argument as a default value for values created using the other constructor.

Trac metadata

Trac field	Value
Version	8.0.1
Type	FeatureRequest
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	libraries/base
Test case
Differential revisions
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Blocking
CC
Operating system
Architecture

changed weight to 5

added Tfeature request Trac import core libraries labels

Trac metadata

Trac field	Value
Differential revisions	- → D2403

closed

Trac metadata

Trac field	Value
Resolution	Unresolved → ResolvedFixed

mentioned in commit a0f83a62

changed milestone to %8.2.1

Thanks mettekou!

added Pnormal label