Re: [q-lang-users] The implicit operator in Q

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

John Cowan wrote:
> This makes me a bit nervous.  Would it be possible to distinguish
> between constants and constructors, and allow a constant in the head
> (but not all constants) while still forbidding a constructor?

That would be a rather arbitrary distinction between constructors of 
zero and nonzero arity.

> The whole point of constructors is that the application of a constructor
> is guaranteed to be in normal form.

Given a declaration like "type BinTree = const bin X T1 T2;" you still 
have that the following equations are all forbidden:

bin = ...;
bin X = ...;
bin X T1 = ...;
bin X T1 T2 = ...;

So, if you have an expression of the form bin X T1 T2 you can still be 
sure that it is a normal form. I guess that this solves your problem?

OTOH, the following equation is now valid:

bin X T1 T2 Y = ...;

Which makes sense if you want to also be able to use an (essentially 
equivalent) equation like:

T:Bintree Y = ...;

I've already implemented it that way, and I've also updated the 
documentation in qdoc.texi. Seems to work nicely so far. If you want to 
try it out, just get yourself the latest qcrules.c from cvs and recompile.

Cheers,
Albert

-- 
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