On Wed, Jun 27, 2007 at 12:48:48PM +0200, Hoehle, Joerg-Cyril wrote:
Albert Krewinkel wrote:
(symbol-macrolet ((el (aref vec row-index col-index))) (... body...)) Macrolet is a possibility, but what about writing a driver that provides access to the 2 index variables, modeled after in-vector? (for x in-vector foo with-index i) (for e in-matrix foo with-indices (i j)) (setf (aref foo i j) bar)
That sure is a good way to do this. Maybe you are right, and the python zen "explizit is better than implicit" applies to this situation as well. But I just feel like it's more verbose than necessary.
BTW, how do you use Iterate to walk across a 2-dimensional thing like a matrix? This would likely involve 2 nested iterations, so any single clause does not provide a complete solution?!?
Regards, Jorg Hohle
A single clause is sufficient for my needs, see code below. It's a quick hack and for testing only, so it's plain ugly. One of my concernes is efficiency. It might be premature optimization, but still: If I do (let ((v (vector 65 42 23 5 105))) (iter (for el in-vector v with-index i) (setf (aref v i) 1)) v) the expansion code will contain (setq el (aref...)). Having a variable to be set to a new value in every iteration, although not needed, doesn't seem to be optimal. Of course I could just iterate using the index, but wouldn't I loose some nice abstractions this way? Thanks for your help Albert <code style="ugly"> (defmacro-driver (FOR var IN-MATRIX matrix &optional WITH-INDICES (indices (list (gensym "ROW") (gensym "COL"))) BY (row-or-column 'column)) (let ((mat (gensym "MAT")) (kwd (if generate 'generate 'for))) (ecase row-or-column ((or column col) (let ((num-cols (gensym "COLS")) (num-rows (gensym "ROWS")) (col-index (car indices)) (row-index (cadr indices))) `(progn ;nlisp (with ,mat = (val ,matrix)) (initially (setq ,col-index 0)) (with ,mat = ,matrix) (with ,num-cols = (array-dimension ,mat 1)) (with ,num-rows = (array-dimension ,mat 0)) (with ,row-index = -1) (generate ,col-index next (incf ,col-index)) (,kwd ,var next (progn (incf ,row-index) (when (>= ,row-index ,num-rows) (if (>= (next ,col-index) ,num-cols) (terminate) (setf ,row-index 0))) (aref ,mat ,row-index ,col-index)))))) ('row (let ((end (gensym "END-INDEX")) (index (gensym "INDEX"))) `(progn ;nlisp (with ,mat = (val ,matrix)) (with ,mat = ,matrix) (with ,end = (array-total-size ,mat)) (with ,index = -1) (,kwd ,var next (progn (incf ,index) (if (>= ,index ,end) (terminate)) (row-major-aref ,mat ,index))))))))) </code>