Control flow with sequences
Factor handbook » The language » Collections » Sequence operations

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To reduce the boilerplate of checking if a sequence is empty, several combinators are provided.

Checking if a sequence is empty:
if-empty ( ..a seq quot1: ( ..a -- ..b ) quot2: ( ..a seq -- ..b ) -- ..b )

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

unless-empty ( ... seq quot: ( ... seq -- ... ) -- ... )