Very very nice! I don't know scheme well... but oh the macros, such a wonderful facility...
Functional lang never let me down. I haven't worked on a Java version yet... but i wonder what pain i'll have to endure for a lang that lacks eval. Since i'm not Java expert... i wonder if i can even do it in a few days. Xah [EMAIL PROTECTED] ∑ http://xahlee.org/ David Van Horn wrote: > Xah Lee wrote: > > here's the Python spec for the Table function: > ... > > References: > > > > • for a context of this message, see: http://xahlee.org/tree/tree.htm > > Here is a Scheme implementation of Table. As noted on your web page and the > Mathematica documentation, the first argument of Table "evaluates in a > non-standard way". Thus we use Scheme macros to control the evaluation of > this expression. The first three clauses in this syntax definition take care > to fill in the default values for i, imin, and di when they are not provided. > The fourth clause iterates over one variable constructing a list. Notice > this is done tail-recursively. The last clause handles the multiple variable > case by rewriting the term into a simpler form. > > (define-syntax table > (syntax-rules () > ((table exp (imax)) > (table exp (i 1 imax 1))) > > ((table exp (i imax)) > (table exp (i 1 imax 1))) > > ((table exp (i imin imax)) > (table exp (i imin imax 1))) > > ((table exp (i imin imax di)) > (let loop ((n imin) (accum '())) > (if (< imax n) > (reverse accum) > (loop (+ n di) (cons ((lambda (i) exp) n) accum))))) > > ((table exp i j ...) > (table (table exp j ...) i)))) > > > ;; Examples > > (table #t (0)) ;; => '() > (table #t (5)) ;; => '(#t #t #t #t #t) > (table i (i 5)) ;; => '(1 2 3 4 5) > (table i (i 2 5)) ;; => '(2 3 4 5) > (table i (i 2 5 2)) ;; => '(2 4) > (table i (i 2 6 2)) ;; => '(2 4 6) > (table (add1 i) (i 2 6 2)) ;; => '(3 5 7) > (table (- i j) (i 2) (j 2)) ;; => '((0 -1) (1 0)) > > (table (list i j k) (i 2) (j 100 200 100) (k 5 6)) > ;; => > '((((1 100 5) (1 100 6)) ((1 200 5) (1 200 6))) > (((2 100 5) (2 100 6)) ((2 200 5) (2 200 6)))) -- http://mail.python.org/mailman/listinfo/python-list
