/prog/ - ENTERPRISE METAPROGRAMMING

Name: Anonymous 2011-01-09 12:48

``ABSTRACT BULLSHITE''

;; range macro that builds a list of numbers at compile-time when possible

;; otherwise, it will be generated at run-time.

(define-syntax (range stx)

  (define gen

    (λ (x y s)

      (let-values (((compare +/-)

                    (if (< x y) (values > +)

                        (values < -))))

        (let loop ((x x)

                   (r '()))

          (if (compare x y) (reverse r)

              (loop (+/- x s)

                    (cons x r)))))))

  (syntax-case stx ()

    ((~ n m s) (let ((n1 (syntax->datum #'n))

                     (m1 (syntax->datum #'m))

                     (s1 (syntax->datum #'s)))

                 (cond ((and (number? n1)

                             (number? m1)

                             (number? s1)) #`'#,(gen n1 m1 s1))

                       (else #`(#,gen n m s)))))

    ((~ n m) #'(~ n m 1))

    ((~ m) (let ((m1 (syntax->datum #'m)))

             (if (number? m1) #`'#,(gen 0 (sub1 m1) 1)

                 #`(#,gen 0 (sub1 m) 1))))))



(range 0 10) ; => '(0 1 2 3 4 5 6 7 8 9 10), builds the list at compile-time.



(define x 10)

(range 0 x) ; => '(0 1 2 3 4 5 6 7 8 9 10), evaluated at run-time.



(range 10 0) ; => '(10 9 8 7 6 5 4 3 2 1 0), compile-time.

(range x 0) ; same, run-time.



(range 0 5 0.5) ; => '(0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5)



(range 10) ; => '(0 1 2 3 4 5 6 7 8 9), builds a list of 10 elements at compile-time.

(range x) ; same, but at run-time.

ENTERPRISE METAPROGRAMMING

1 Name: Anonymous 2007-10-10 8:24

11 Name: Anonymous 2011-01-09 12:48

Name: Anonymous 2007-10-10 8:24

Name: Anonymous 2011-01-09 12:48