Yes, the -> is fine. And, so is doing the same bounds check in my own procedure. I was surprised that the ->d was so much slower. I use contracts regularly and was trying to expand my usage of them. <div class="gmail_quote"> On Sat, Apr 11, 2009 at 12:46 PM, Robby Findler <<a href="mailto:robby@eecs.northwestern.edu">robby@eecs.northwestern.edu</a>> wrote: <blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;"> ->d is definitely substantially slower than the other because the wrappers are more complex. Are you finding the performance overhead of the ordinary -> acceptable? Robby <div><div></div><div class="h5"> On Sat, Apr 11, 2009 at 1:17 PM, Doug Williams <<a href="mailto:m.douglas.williams@gmail.com">m.douglas.williams@gmail.com</a>> wrote: > I would like to use ->d to impose a precondition for a function. For > example: > > (matrix-ref > (->d ((matrix matrix?) > (i (and/c exact-nonnegative-integer? (</c (matrix-rows matrix)))) > (j (and/c exact-nonnegative-integer? (</c (matrix-cols matrix))))) > () > (result any/c))) > > or > > (matrix-ref > (->d ((matrix matrix?) > (i exact-nonnegative-integer?) > (j exact-nonnegative-integer?)) > () > #:pre-cond (and ( > (< j (matrix-cols matrix))) > (result any/c))) > > instead of just > > (matrix-ref > (-> matrix? exact-nonnegative-integer? exact-nonnegative-integer? any/c)) > > The first two do work, but are really, really slow. > > I like having the bounds check in the contract (as opposed to bounds check > in the matrix-ref code, but can't accept the performance hit. Any ideas? > > Doug > > </div></div>> _________________________________________________ > For list-related administrative tasks: > <a href="http://list.cs.brown.edu/mailman/listinfo/plt-scheme" target="_blank">http://list.cs.brown.edu/mailman/listinfo/plt-scheme</a> > > </blockquote></div>