Re: [q-lang-users] newbie question: Efficiency & other stuff

[Albert G. <Dr....@t-...>]

Arnoldo Jose Muller Molina wrote:
> dmatch(E1,E2) = (#expand(E1) + #expand(E2)) - (2 * dmatchAux(expand
> (E1),expand(E2)));

As Q functions may have side effects, it is not possible to optimize 
away shared subexpressions like this. That's what where clauses are for. 
Try something like:

dmatch(E1,E2) = (#X1 + #X2) - (2 * dmatchAux(X1,X2))
   where X1 = expand(E1), X2 = expand(E2);

> I have executed some stats commands after executing this rule, with and
> without the "(#expand(E1) + #expand(E2))" and it seems that q is
> calculating expand(E1) and expand(E2) 2 times (1). 
> 
> 1) Is this true?
> 
> 2) if that is so, is there a way of implementing a "let" so I can
> compute only once the results of expand(_)? Of course I could create an
> elaborate chain of rules and allow this, but is there a way that doesn't
> involve creating several rules? 
> 
> Thank you!
> 
> --------------------------
> (1) (expand(...) is a deterministic rule, it will always return the same
> result for the same input)

-- 
Dr. Albert Gr"af
Dept. of Music-Informatics, University of Mainz, Germany
Email:  Dr....@t-..., ag...@mu...
WWW:    http://www.musikinformatik.uni-mainz.de/ag