Re: [q-lang-users] where

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

Eddie Rucker wrote:
> Dr. Graef and (Mr? Dr?) Hubbard,

No need to throw around titles here, we're all friendly people. ;-)

That reminds me of a "Hägar the Horrible" strip in which Hägar asks his
medical doctor, Dr. Zook, whether he is allowed to call him by his first
name. "Yes sure," Dr. Zook replies. "So what's your first name?" asks
Hägar. The reply: "Doctor." :)

Ok, back on topic...

> Of all of the functions in mathematics that I've ever seen, if a "where
> clause" is given at the end of a piecewise function, the variables and/or
> functions denoted by "where" are global to all of the "pieces."

That's true, although some mathematicians (me included) occasionally use
local "where" clauses in branches, too. A syntax which closely mimics
this style could maybe look like this:

foo X = ... Y ... where ... if ...,
      = ... Y ...,
where Y = ...;

But that's awkward to parse, since the entire collection of equations
must be in memory before you can start generating code.

> let N = #S - 1;
> strip C S = strip C $ sub S 0 (N-1) if (S!N = C);

This looks like the "let" and the following equation(s) are totally
unrelated. Not a good syntax IMHO.

> Another idea, so that wheres are nested:
> 
> f X Y Z
>   where A = ... ; // global to all equations belonging to f
>      = ...;
>      = ...;
>   where B = ... ; // global to all equations below this and belonging to f
>      = ...;
>      = ...;
>   where C = ... where D = ...;
>      = ...;

That's a neat idea, but still not fully general. What if you want A to
be defined only in eqns #1 and #2 and B only in eqns #3 and #4? You need
some kind of block structure to do that. And IMHO block structure looks
messy in equational programs, at least in a free-format language like Q
where you need explicit brackets to indicate the block structure.

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