Re: [pure-lang-users] C macros

[Eddie R. <er...@bm...>]

On Tue, 2008-08-26 at 02:54 +0200, Albert Graef wrote:
> Better yet: HYGIENIC macros. :-P

I'm looking forward to playing with this.

> I'm falling asleep at the keyboard (past 2:30am over here), will reply 
> to your questions in more detail tomorrow. Just some quick remarks:

I would probably do this to if I had a computer at home. It is probably
best that I don't because I would never get anything around the house
done ;-)

>  You can make a C function fail, but only if it returns an expr* 
> (pure_expr* on the C side), then you can just return a null pointer. So 
> you need to provide a wrapper for the GSL function which returns a real 
> pure_expr*, that's probably not what you want I guess. But for hard 
> error conditions like alloc failure it would be ok to just throw a Pure 
> exception, no?

In csv.c and csv.pure I just invoked an error rule with a message about
the error. Maybe I should revisit csv.c and throw a Pure exceptions in
the alloc cases?

> - I'd eventually like the GSL matrices to be some kind of native type in 
> Pure if possible. For the time being, I'd suggest to wrap them up in a 
> Pure constructor (matrix p or something like that where p is the pointer 
> to the GSL struct or whatever it is).

Yes, it is a GSL struct. I've been playing with the following
constructor.

Matrix (x:xs) = (gsl_matrix_alloc rows cols, rows, cols)
		when 
		  rows = #(x:xs);
		  cols = #x
                end;

To take a list of lists to convert it to the GSL struct and returns a
tuple with the pointer, the number of rows and cols. Since I can access
fields, I can completely do away with the rows and cols and access the
rows and cols with getter functions. Now, I just need a constructor for
a zero matrix and an identity matrix.

So you're suggesting to differentiate matrices and vectors. I should do
something like

Matrix (x:xs) = matrix (gsl_matrix_alloc rows cols)
	when
	  rows = #(x:xs);
	  cols = #x
	end;

and 

Vector (x:xs) = vector (gsl_vector_alloc len)
	when len = #(x:xs) end;

?

Then the operations become:

(matrix a) + (matrix b) = ...
(vector a) + (vector b) = ... 

Am I following correctly?

> - Accessing the fields of a struct through pointers in Pure is possible 
> (see the stuff at the end of primitives.pure), but probably 
> non-portable. You'd probably need some getter/setter functions in your 
> wrapper to do that in a safe way.

Got it.

I hope you got a good rest.

e.r.