:: a -> () -package:ghc-lib -package:unsafe package:control-dsl

Lift r to the answer type, similar to return. This return function aims to be used as the last statement of a do block. When return is present in a nested do block for when or unless, if the r' is not (), it will create a Cont that performs early return, skipping the rest statements of the outer do notation.

Examples

>>> :set -XTypeOperators

>>> :set -XRebindableSyntax

>>> import Prelude hiding ((>>), (>>=), return, fail)

>>> import Control.Dsl

>>> import Control.Dsl.Return

>>> import Control.Dsl.Yield

>>> import Control.Dsl.Cont

>>> import Control.Dsl.Empty

>>> :{
earlyGenerator :: Bool -> Cont [String] Integer
earlyGenerator earlyReturn = do
Yield "inside earlyGenerator"
when earlyReturn $ do
Yield "early return"
return 1
Yield "normal return"
return 0
:}

>>> :{
earlyGeneratorTest :: [String]
earlyGeneratorTest = do
Yield "before earlyGenerator"
i <- earlyGenerator True
Yield "after earlyGenerator"
Yield $ "the return value of earlyGenerator is " ++ show i
empty
:}

>>> earlyGeneratorTest
["before earlyGenerator","inside earlyGenerator","early return","after earlyGenerator","the return value of earlyGenerator is 1"]