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

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

Hi Marco,

ma...@ma... wrote:
> I just got burned by this unexpected (for me, of course) behavior of
> list comprehension.  Given the program
> 
>    delta X X      = 1;
>    delta _ _      = 0 otherwise;
>    tabulate N M F = [[F I J : I in [1..N]] : J in [1..M]];
>    eye N          = tabulate N N delta;
> 
> then (eye 2) evaluates to [[0,0],[0,0]] instead of [[1,0],[0,1]] as I
> would have imagined.

Yes, your imagination is certainly right. ;-) [delta I J : I in [1..2],
J in [1..2]] does the right thing, so it seems to be an issue with the
nested listof. Maybe a bug crept in there when the matching semantics
were slightly changed in Q 7.1, so that the nested listof now gets
evaluated too early. I'll look into it, thanks for the report!

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