[plt-scheme] Okay, this is ugly

Your version is ugly because you are thinking in C (or some similar ugly language).
I think that real Scheme code can't be ugly.

Sincerely,
Chongkai Zhu  

======= At 2006-02-18, 07:46:24 Chongkai Zhu wrote: =======

>CPS:
>
>(define (env-get-binding s env)
>  (if (null? env)
>      (void) ;;or, (error ...)
>      (hash-table-get (car env)
>                      s
>                      (lambda ()
>                        (env-get-binding s (cdr env))))))
>
>Sincerely,
>Chongkai Zhu  
>
>======= At 2006-02-18, 01:13:12 Gregory Woodhouse wrote: =======
>
>>The idea here is that env is a list of hash tables (created, for  
>>example, by let), and when looking up a symbol, I want to start with  
>>the car of env and return the binding I find there (if there is one).  
>>Otherwise, I want to keep looking by repeating the process using the  
>>cdr of env, until it's empty.
>>
>>The following code seems to work, but it's ugly because it uses the  
>>failure thunk of hash-table-get to return #<void> if no binding is  
>>found, and then uses this as a kind of sentinel value to indicate  
>>that the code should recur on the list.
>>
>>(define (env-get-binding s env)
>>   (call/cc
>>    (lambda (k)
>>      (if (null? env) k (void))
>>      (let ((t (hash-table-get (car env) s (lambda () (void)))))
>>        (unless (void? t) (k t)
>>          (env-get-binding s (cdr env)))))))
>>
>>Using sentinel values like this seems unidiomatic and rather awkward.  
>>Surely, there is a cleaner (clearer?) way to do this.
>>
>>==
>>Gregory Woodhouse
>>gregory.woodhouse at sbcglobal.net
>>
>>"If you give someone Fortran, he has Fortran.
>>If you give someone Lisp, he has any language he pleases."
>>--Guy L. Steele, Jr.
>>
>>
>>
>>
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