Hashtables

[Nic F. <nfe...@ta...>]

One of the TODO items is hashtable code.

I have a hashtable interface that I have written for my XML parser
(to store attributes).

I wanted to write a pure functional hashtable that could still
interface to the Java implementations but I haven't been able to find
a good enough description of a functional hashtable so the one I've
got now is kind of a "wanna-be".

Here's the code:


;;Hash handling
;;(c) Nic Ferrier - Tapsell-Ferrier Limited
;;
;;a simple Kawa interface to Java hash tables.
;;Could be implemented as native Scheme if necessary.
;;

(module-export put)
(module-export get)
(module-export remove)


;;add a pair to a hashtable
;;=<java.util.Map> the hash
;;
;;This is a slightly recursive version that creates the hash
;;if it doesn't exist
;;
(define (put key value hashtable :: <java.util.Map>) ::
<java.util.Map>
  (if (eqv? hashtable #!null)
      (let ((hashtable (make <java.util.Hashtable>)))
	(put key value hashtable))
      (let ((real-key (invoke key 'to-string)))
	(invoke hashtable 'put real-key value)
	hashtable)
      )
  )

;;get a value specified by key from the hashtable
;;=value assigned to the key or #f if not found
;;
(define (get key hashtable :: <java.util.Map>)
  (let ((got (invoke hashtable 'get key)))
    (if (eqv? got #!null)
	#f
	got)
    )
  )

;;remove a value specified by key from the hashtable 
;;=value removed or #f if not found
;;
(define (remove key hashtable :: <java.util.Map>)
  (let ((removed (invoke hashtable 'remove key)))
    (if (eqv? removed #!null)
	#f
	got)
    )
  )



Harsh or fair critisism appreciated. 

My intention is for this to be a "this is how it might be done" and
for some discussion to improve it. The improved hashtable can then be
adopted into BRL?


Nic Ferrier