From Newsgroup: comp.lang.lisp

Nathan Baum wrote:

Then suppose you later need the loop/map to collect some of the values
under certain conditions. You might have

(loop for x in (get-list)
for i from 0
do (format t "~A - ~A~%" i x)
if (test x)
collect (foo x))

Gauche Scheme

(filter-map
(lambda (x i)
(print i " - " x)
(and (odd? x) (square x)))
'(0 2 3 5 6 9)
(liota))

===>
0 - 0
1 - 2
2 - 3
3 - 5
4 - 6
5 - 9
(9 25 81)
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From Newsgroup: comp.lang.lisp

Pascal Costanza wrote:

- More often than not, the different variables actually iterate over different kinds of values. Recently, I needed the following costruct
quite often:

(loop for x in some-list
for i from 0
collect `(,x ,i))

This enumerates all elements in a list. You would have to express this completely manually without LOOP because none of the mapxyz functions
help you here.

Wrong.

Gauche Scheme:

(map list some-list (lrange 0))

Another way:

(use gauche.sequence :only (map-with-index))
(use srfi-1 :only (xcons))

(map-with-index xcons '(20 30 40 50))

((20 . 0) (30 . 1) (40 . 2) (50 . 3))
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From Newsgroup: comp.lang.lisp

Nathan Baum wrote:

Suppose you have

(loop for x in (get-list)
do (format t "~A~%" x))

and then it turns out you need to print a numeric index. You can do

(loop for x in (get-list)
for i from 0
do (format t "~A - ~A~%" i x))

If you start with

(mapc (lambda (x) (format t "~A~%" x)) (get-list))

it seems (to me) that it'd be harder to modify it as needed,

(let ((list (get-list)))
(mapc (lambda (i x) (format t "~A - ~A" i x))
(range 0 (length list))
list))

(I'm assuming the toolkit includes a RANGE utility, or something similar.)

Gauche Scheme

Shorter than the loop:

(for-each
(cut print <> " - " <>)
(lrange 0)
'(a b c))

0 - a
1 - b
2 - c


(for-each
(cut print <> " - " <> " - " <>)
(lrange 0)
'(a b c)
'(! ? @))

0 - a - !
1 - b - ?
2 - c - @



(use srfi-42) ; do-ec

(do-ec (:list x (index i) '(a b c)) (print i " - " x))

0 - a
1 - b
2 - c
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From Newsgroup: comp.lang.lisp

B. Pym wrote:

Nathan Baum wrote:

Suppose you have

(loop for x in (get-list)
do (format t "~A~%" x))

and then it turns out you need to print a numeric index. You can do

(loop for x in (get-list)
for i from 0
do (format t "~A - ~A~%" i x))

If you start with

(mapc (lambda (x) (format t "~A~%" x)) (get-list))

it seems (to me) that it'd be harder to modify it as needed,

(let ((list (get-list)))
(mapc (lambda (i x) (format t "~A - ~A" i x))
(range 0 (length list))
list))

(I'm assuming the toolkit includes a RANGE utility, or something similar.)

Gauche Scheme

Shorter than the loop:

(for-each
(cut print <> " - " <>)
(lrange 0)
'(a b c))

0 - a
1 - b
2 - c

(for-each
(cut print <> " - " <> " - " <>)
(lrange 0)
'(a b c)
'(! ? @))

0 - a - !
1 - b - ?
2 - c - @

(use srfi-42) ; do-ec

(do-ec (:list x (index i) '(a b c)) (print i " - " x))

0 - a
1 - b
2 - c

Nathan Baum wrote:

Then suppose you later need the loop/map to collect some of the values
under certain conditions. You might have

(loop for x in (get-list)
for i from 0
do (format t "~A - ~A~%" i x)
if (test x)
collect (foo x))

Gauche Scheme

(use srfi-42)

(list-ec (:list x (index i) '(0 -2 3 4 -7 9))
(begin (print i " : " x))
(if (negative? x))
(abs x))

0 : 0
1 : -2
2 : 3
3 : 4
4 : -7
5 : 9
(2 7)

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