<step-slice> ( from/f to/f step seq -- step-slice )

Vocabulary

sequences.extras

Inputs

from/f	an integer or f
to/f	an integer or f
step	an object
seq	a sequence

Outputs

step-slice

a slice

Word description

Outputs a new virtual sequence sharing storage with the subrange of elements in seq with indices starting from and including from/f, and up to but not including to/f, with step step.

If fis given in place of from/f, it is taken as 0.

If fis given in place of to/f, it is taken as the length of seq.

Definition

USING: kernel math math.order sequences ;

IN: sequences.extras

:: <step-slice> ( from/f to/f step seq -- step-slice )
    step zero? [ "can't be zero" throw ] when
    seq length :> len step 0 >
    [ from/f [ 0 ] unless* to/f [ len ] unless* ]
    [ from/f [ len ] unless* to/f [ 0 ] unless* ] if
    [ dup 0 < [ len + ] when 0 len clamp ] bi@ seq dup slice?
    [ collapse-slice ] when step step-slice boa ;