Le 30 mai 09 à 10:20, Mark Polesky a écrit :
Here's another useful set of procedures that is not in
lily-library.scm. These functions make quick work of calculating
offsets, extents, bounding-boxes, etc.
Here's a new patch that also incorporates conditionals.
;; defines 14 functions:
;; pair_+ pair_- pair_* pair_/
;; pair_= pair_< pair_> pair_<= pair_>=
;; pair_gcd pair_lcm pair_min pair_max pair_average.
;; eg. (pair_+ '(1 . 1) '(2 . 3) '(5 . 8)) ==> (8 . 12)
;; (pair_<= '(1 . 8) '(1 . 5) '(2 . 3)) ==> (#t . #f)
;; (pair_min '(1 . 8) '(1 . 5) '(2 . 3)) ==> (1 . 3)
(map primitive-eval
(map
(lambda (f)
`(define-public
(,(symbol-append 'pair_ f) . pairs)
(apply (lambda (f . pairs)
((lambda (lst) (cons (car lst) (cadr lst)))
(primitive-eval
(append `(map ,f)
(map (lambda (x) `(list ,(car x) ,(cdr x)))
pairs)))))
,f pairs)))
'(+ - * / = < > <= >= gcd lcm min max average)))
This is not the way to do it in guile scheme. When you find yourself
using primitive-eval, ask yourself if there is not a better way.
To write code that writes codes, use macros: read about defmacro.
Also note that you usually don't use underscores in function names.
But in that particular case, why not define a function that takes
a function and a list of pairs? It's usual to have procedure arguments:
(define (map-on-pairs fn pairs)
(cons (apply fn (map car pairs))
(apply fn (map cdr pairs))))
(map-on-pairs + '((1 . 1) (2 . 3) (5 . 8))) => (8 . 12)
(map-on-pairs min '((1 . 8) (1 . 5) (2 . 3))) ==> (1 . 3)
nicolas
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