Re: [q-lang-users] "listof" surprises

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

/me wrote:
> Unfortunately, the above won't work yet if you define 'let' in terms of
> 'case', because 'case' expressions aren't an instance of 'Lambda' right
> now. Should they be? Probably. Another item for the Q 7.7 TODO list...

Ok, this is fixed now. Thus the following alternative definition of
'let' will now work as expected:

type Let : Lambda = special let B X;
let (A=Z) X = case Z (A,X;);
lambdax (let (A=Z) X) = '(case Z (A,X;));

As a bonus, I've also added two special forms 'condfun' and 'casefun'
which allow you to create conditional and pattern-matching abstractions,
which take their data as the second parameter. I.e., 'casefun' is just
'case' with its arguments reversed, which provides you with a means to
quickly define an anonymous p.-m. function, e.g.:

==> casefun ((X,Y),X*Y;X,X) (2,3)
6

Similarly, 'condfun' applies the predicate P from each branch (P,X) to
the extra parameter Y and, if it yields true, returns the corresponding
X Y. For instance, here's a rather contrived way to describe the sign
function:

==> condfun ((>0),cst 1;(<0),cst (-1);(=0),cst 0) 0
0

In fact, both 'case' and 'casefun' are now instances of 'Lambda' which
just expand to an equivalent 'condfun' expression.

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