?first ( seq -- elt/f )
Factor handbook » The language » Collections » Sequence operations » Accessing sequence elements

Prev:	fourth ( seq -- fourth )
Next:	?second ( seq -- elt/f )

Vocabulary
sequences

Inputs

seq	a sequence

Outputs

elt/f

an object or f

Word description
A forgiving version of first. If the sequence is empty, or if the sequence is f, simply outputs f.

Examples
On an empty sequence:

USING: sequences prettyprint ; { } ?first .
f

Works like first on sequences with elements:

USING: sequences prettyprint ; { 1 2 3 } ?first .
1

Definition

USING: kernel ;

IN: sequences

: ?first ( seq -- elt/f ) 0 swap ?nth ; inline