Hash tables

Hash tables

[Nick Roberts]

I am trying to using alists to store information (to display watched expressions
under gdb with the speedbar). I have expressions like:

(dolist (var gdb-var-list)
     (let ((var-list))
       some operation on var...
     (push var var-list))
(setq gdb-var-list (nreverse var-list)))

where var is a list like (varnum a b c d)

Update of the speedbar for arrays and structures is too slow, so I thought
hash tables might speed things up. I want to replace the above with something
like:

(maphash gdb-var-operation gdb-var-table)

The manual says that gdb-var-operation, should accept two arguments KEY and
VALUE.

but I want to pass some arguments to gdb-var-operation. I plan to change
maphash to:

(maphash FUNCTION TABLE &optional ARGS)

so that FUNCTION gets called with KEY, VALUE and ARGS.

This won't be an easy task for me so I'd like some reassurance that its
a) desirable and b) do-able.


Nick

Re: Hash tables

[Miles Bader]

On Thu, Sep 11, 2003 at 11:12:38PM +0100, Nick Roberts wrote:
> but I want to pass some arguments to gdb-var-operation. I plan to change
> maphash to:
> 
> (maphash FUNCTION TABLE &optional ARGS)
> 
> so that FUNCTION gets called with KEY, VALUE and ARGS.
> 
> This won't be an easy task for me so I'd like some reassurance that its
> a) desirable and b) do-able.

The traditional way of doing this sort of thing in lisp is to bind variables
around the call to maphash, which your function can read (or write), e.g.:

   (let ((extra-info ...)
	 (total sum 0))
     (maphash
      (lambda (key val) 
	(setq total (+ total (calculate-stuff key val extra-info))))
      some-hash-table))

-Miles
-- 
We have met the enemy, and he is us.  -- Pogo

Re: Hash tables

[Stefan Monnier]

> but I want to pass some arguments to gdb-var-operation. I plan to change
> maphash to:
> (maphash FUNCTION TABLE &optional ARGS)
> so that FUNCTION gets called with KEY, VALUE and ARGS.

That is not necessary.  You can just use

  (maphash `(lambda (key value) (fun key value ',arg)) table)

instead.  And in most cases the above can even be simplified to

  (maphash (lambda (key value) (fun key value arg)) table)


        Stefan