XPost: comp.lang.scheme

Pascal Costanza wrote:

(loop for x in '(1 2 3)
for y in '(4 5 6)
collect (* 2 (+ x y)))

vs.

(mapcar (lambda (x y)
(* 2 (+ x y)))
'(1 2 3)
'(4 5 6))

However, what if there were 9 lists instead of 2?
The CL (COBOL-Like) version would become:

(loop for a in '(1 2 3)
for b in '(4 5 6)
for c in '(7 8 9)
for d in '(20 21 22)
for e in '(23 24 25)
for f in '(26 27 28)
for g in '(29 30 31)
for h in '(32 33 34)
for i in '(35 36 37)
collect (* 2 (+ a b c d e f g h i)))


(354 372 390)

The Scheme version would simply become:

(map (~>> + (* 2))
'(1 2 3)
'(4 5 6)
'(7 8 9)
'(20 21 22)
'(23 24 25)
'(26 27 28)
'(29 30 31)
'(32 33 34)
'(35 36 37))

===>
(354 372 390)

Given:

(define-syntax ->>
(syntax-rules ()
[(_ x) x]
[(_ x (y ...) z ...)
(->> (y ... x) z ...)]
[(_ x y z ...)
(->> (y x) z ...)]))

(define-syntax ~>>
(syntax-rules ()
[(_ (func0 a ...) func ...)
(lambda xs (->> (apply func0 a ... xs) func ...))]
[(_ func0 func ...)
(lambda xs (->> (apply func0 xs) func ...))]))

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