Re: [Chicken-users] Hashtable is behaving unexpectedly

[Felix Winkelmann]

Michael Erdmann wrote:
> Dear all the code fragement below works as expected:
>
> (define h (make-hash-table))
>
> (define A_Age 'Age)
> (define Michael "Michael")
>
> (put! h Michael A_Age 45)
> (write (get h Michael A_Age )) (newline)
> (write (hash-table-ref h Michael)) (newline)
>
> (write (hash-table->list h)) (newline)                    
>
> address@hidden:~/scheme/x> ./ht
> 45
> ((Age . 45))
> (("Michael" (Age . 45)))
>
> _but_ when i am replacing Michael by "Michael" every where
> where i invoke get it fails. Probly because they are not
> the same objects.
>
> Why is it like this implemented? It is not very helpfull
> in this implementation, or did i miss something?

It depends on the comparison function used by the hash-table.
The default is eqv?, but you can pass the desired function
to make-hash-table:

(define h (make-hash-table string=?))

eqv? is more efficient, so it is the default.

cheers,
felix