if-empty ( ..a seq quot1: ( ..a -- ..b ) quot2: ( ..a seq -- ..b ) -- ..b )
Factor handbook » The language » Collections » Sequence operations » Control flow with sequences

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when-empty ( ... seq quot: ( ... -- ... obj ) -- ... seq/obj )

Vocabulary
sequences

Inputs

seq	a sequence
quot1	a quotation
quot2	a quotation

Outputs
None

Word description
Makes an implicit check if the sequence is empty. An empty sequence is dropped and quot1 is called. Otherwise, if the sequence has any elements, quot2 is called on it.

Examples

USING: kernel prettyprint sequences ; { 1 2 3 } [ "empty sequence" ] [ sum ] if-empty .
6

Definition

USING: kernel ;

IN: sequences

: if-empty
    ( ..a seq quot1: ( ..a -- ..b ) quot2: ( ..a seq -- ..b ) -- ..b )
    [ dup empty? ] [ [ drop ] prepose ] [ ] tri* if ; inline