undo-if-empty ( result a b -- seq )

Vocabulary

inverse

Inputs

result	an object
a	an object
b	an object

Outputs

seq

an object

Definition

USING: combinators kernel ;

IN: inverse

:: undo-if-empty ( result a b -- seq )
    a ( -- b ) call-effect result =
    [ { } ] [ result b [undo] ( a -- b ) call-effect ] if ;