unless* ( ..a ? false: ( ..a -- ..a x ) -- ..a x )
Factor handbook » The language » Combinators » Conditional combinators

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Vocabulary
kernel

Inputs

?	a generalized boolean
false	a quotation with stack effect ( ..a -- ..a x )

Outputs

x

an object

Word description
Variant of if* with no true quotation.

Notes
The following two lines are equivalent:

X [ Y ] unless* X dup [ ] [ drop Y ] if

Definition

IN: kernel

: unless* ( ..a ? false: ( ..a -- ..a x ) -- ..a x )
    over [ drop ] [ nip call ] if ; inline