head? ( seq begin -- ? )
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Vocabulary
sequences

Inputs

seq	a sequence
begin	a sequence

Outputs

?

a boolean

Word description
Tests if seq starts with begin. If begin is longer than seq, this word outputs f.

Examples

USING: prettyprint sequences ; { "accept" "adept" "advance" "advice" "affect" } [ "ad" head? ] filter .
{ "adept" "advance" "advice" }

Definition

USING: kernel sequences.private ;

IN: sequences

: head? ( seq begin -- ? )
    2dup shorter?
    [ 2drop f ] [
        [ length [ head-slice ] keep swap ] keep mismatch-unsafe
        not
    ] if ;