Re: [q-lang-users] New 'where' syntax

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

Keith Trenton wrote:
> - In Q this definition can now be written as follows:
> - clunky ENV VAR1 VAR1
> -    where just VAL1 = lookup ENV VAR1,
> -          just VAL2 = lookup ENV VAR2: <<<<<
> 
> Is that colon ':' following 'VAR2' correct? It doesn't look right, but I know that I have probably missed something along the way... (so I'm asking you nicely for clarification =).

Yes it is... Some kind of proper delimiter which terminates the list of
lhs qualifiers/guards was needed (both for readability purposes, and to
resolve actual ambiguities in the grammar). I first considered ',', but
this wasn't possible since ',' also delimits different definitions in a
'where' clause, and ';' looked awful (as if the equation ended
prematurely). I think that ':' is a fairly good choice; if properly
formatted, it makes the lhs qualifiers stick out like a kind of "case
labels", as shown in my revision of Eddie's original 'strip' example in
my previous post:

        strip C S
        where N = #S-1 if not null S:
                = strip C $ sub S 0 (N-1) if S!N = C;
                = strip C $ sub S 1 N if S!0 = C;
        otherwise:
                = S;

-- 
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