Either
Monadics

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Vocabulary
monadics

Word description
An Either value holds either a "correct" Right value or a Left value, usually signifying an error of some kind. Any action over a Left value preserves the Left value instead.

USING: math monadics prettyprint ; [ + ] 5 right <$> "Bad Input" left <*> .
T{ Left { value "Bad Input" } }

See also
?either, validate

Definition

IN: monadics

MIXIN: Either INSTANCE: Left Either INSTANCE: Right Either

Methods

USING: accessors kernel monadics ;

M: Either and-then
    over Right? [ [ value>> ] dip lazy-call ] [ drop ] if ;


USING: kernel monadics ;

M: Either choose dup Right? [ drop ] [ nip ] if ;


USING: accessors kernel monadics ;

M: Either fmap
    over Right? [ [ value>> ] dip lazy-call right ] [ drop ] if
    ;


USING: monadics ;

M: Either pure right ;


USING: accessors kernel monadics ;

M: Either reify
    2dup [ Right? ] bi@ and
    [ [ value>> ] bi@ swap lazy-call right ]
    [ dup Left? [ nip ] [ drop ] if ] if ;