# [plt-dev] n-valued list and vector sequences

I've found these functions very useful and I'd like to add them to the
core. I'm not sure what a good naming convention is. Perhaps just
in-list and in-vector with an additional argument. What do you think?
#lang scheme
(require tests/eli-tester)
(define (in-list* l n)
(make-do-sequence
(lambda ()
(values (lambda (l) (apply values (take l n)))
(lambda (l) (drop l n))
l
(lambda (l) (>= (length l) n))
(lambda _ #t)
(lambda _ #t)))))
(define l (list 1 2 3 4))
(test
(for/list ([i (in-list l)]) i) => '(1 2 3 4)
(for/list ([i (in-list* l 1)]) i) => '(1 2 3 4)
(for/list ([(i j) (in-list* l 2)]) (cons i j)) => '((1 . 2) (3 . 4))
(for/list ([(i j k) (in-list* l 3)]) (list i j k)) => '((1 2 3)))
(define (in-vector* v n)
(make-do-sequence
(λ ()
(values (λ (i) (vector->values v i (+ i n)))
(λ (i) (+ i n))
0
(λ (i) (>= (vector-length v) (+ i n)))
(λ _ #t)
(λ _ #t)))))
(define v (vector 1 2 3 4))
(test
(for/list ([i (in-vector v)]) i) => '(1 2 3 4)
(for/list ([i (in-vector* v 1)]) i) => '(1 2 3 4)
(for/list ([(i j) (in-vector* v 2)]) (cons i j)) => '((1 . 2) (3 . 4))
(for/list ([(i j k) (in-vector* v 3)]) (list i j k)) => '((1 2 3)))
--
Jay McCarthy <jay at cs.byu.edu>
Assistant Professor / Brigham Young University
http://teammccarthy.org/jay
"The glory of God is Intelligence" - D&C 93