Thread: [Jscheme-user] Testing if a symbol is bound?

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jscheme-user

[Jscheme-user] Testing if a symbol is bound?

From: Michael T. <mt...@bb...> - 2006-01-10 20:10:55

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What is the "proper" way to test to see if a symbol is bound?<br>
<br>
I was expecting something like (bound? 'foo).<br>
<br>
I've been using (.isDefined 'foo) but surely there is something
better...<br>
<br>
Thanks,<br>
&nbsp;&nbsp;&nbsp; mik<br>
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      <font color="#808080" size="2"><b>Michael Thome</b></font><br>
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Re: [Jscheme-user] Testing if a symbol is bound?

From: Timothy J H. <tjh...@br...> - 2006-01-10 21:43:20

Hi mik,

On Jan 10, 2006, at 3:10 PM, Michael Thome wrote:
>  What is the "proper" way to test to see if a symbol is bound?
There is no proper way, as far as I can tell.
>
>  I was expecting something like (bound? 'foo).
If you have created a scheme environment using the jscheme.JScheme 
constructor,
then there is an isDefined method which tests whether a symbol is 
defined in that interpreter,
e.g.

> [Timothy-Hickeys-Computer:~/Research/Software/jscheme] tim% java -jar 
> lib/jscheme.jar
> JScheme 7.2 (1/10/06 8:55 AM) http://jscheme.sourceforge.net
> > (define js (jscheme.JScheme.))  ;; create a new scheme interpreter
> $1 = jscheme.JScheme@5db13f
>
> > (.eval js '(define x 1))   ;; evaluate a define in that interpreter
> $2 = 1
>
> > (.isDefined js "x")   ;; check to see if the symbol corresponding to 
> the string "x" is defined in that interpreter
> $3 = #t
>
> > (.isDefined js "y")  ;; notice that "y" is not defined
> $4 = #f
>
> > (.isDefined 'x)  ;; also notice that 'x is not defined in the 
> toplevel Scheme environment, only in js
> $5 = #f
>
> > (.eval js 'x)  ;; we can get the value of 'x in js using eval 
> again....
> $6 = 1
>

If you want to check whether a symbol is defined in the toplevel then 
(.isDefined 'foo) works fine.
You could also use a macro with tryCatch  to test for defined-ness 
without having to quote the symbol...

> > (tryCatch (begin x #t) (lambda(e) #f))
> $7 = #f
>
> > (define-macro (isDefined s) `(tryCatch (begin ,s #t) (lambda(e) #f)))
> $8 = (macro isDefined (s)...)
>
> > (isDefined sin)
> $9 = #t
>
> > (isDefined sine)
> $10 = #f


I like the try/Catch approach better because the (.isDefined 'x) relies 
on the implementation of the Symbol.java class
in the jsint package, which could conceivably change at some point, 
whereas the tryCatch approach relies only on
the syntax of macros and tryCatch and the fact that evaluating an 
undefined symbol generates an exception....
But, using (.isDefined 'foo) is ten times faster then the tryCatch 
approach  ...

>
> > (time (isDefined foo) 100000)
> $10 = (#f (2929 msec) (367880 bytes))
>
> > (time (.isDefined 'foo) 100000)
> $11 = (#f (211 msec) (135856 bytes))

Does that help??

Best,
---Tim---

Re: [Jscheme-user] Testing if a symbol is bound?

From: Geoffrey K. <ge...@kn...> - 2006-01-11 09:02:09

Good question.  MIT/GNU Scheme has:

procedure: environment-reference-type environment symbol

Returns a symbol describing the reference type of symbol in  
environment or one of its ancestor environments.   The result is one  
of the following:

normal - means symbol is a variable binding with a normal value.
unassigned - means symbol is a variable binding with no value.
macro - means symbol is a keyword binding.
unbound - means symbol has no associated binding.

http://www.gnu.org/software/mit-scheme/documentation/scheme_14.html

Geoffrey
--
Geoffrey S. Knauth | http://knauth.org/gsk


On Jan 10, 2006, at 16:42, Timothy J Hickey wrote:

> Hi mik,
>
> On Jan 10, 2006, at 3:10 PM, Michael Thome wrote:
>>  What is the "proper" way to test to see if a symbol is bound?
> There is no proper way, as far as I can tell.
>>
>>  I was expecting something like (bound? 'foo).
> If you have created a scheme environment using the jscheme.JScheme  
> constructor,
> then there is an isDefined method which tests whether a symbol is  
> defined in that interpreter,
> e.g.
>
>> [Timothy-Hickeys-Computer:~/Research/Software/jscheme] tim% java - 
>> jar lib/jscheme.jar
>> JScheme 7.2 (1/10/06 8:55 AM) http://jscheme.sourceforge.net
>> > (define js (jscheme.JScheme.))  ;; create a new scheme interpreter
>> $1 = jscheme.JScheme@5db13f
>>
>> > (.eval js '(define x 1))   ;; evaluate a define in that interpreter
>> $2 = 1
>>
>> > (.isDefined js "x")   ;; check to see if the symbol  
>> corresponding to the string "x" is defined in that interpreter
>> $3 = #t
>>
>> > (.isDefined js "y")  ;; notice that "y" is not defined
>> $4 = #f
>>
>> > (.isDefined 'x)  ;; also notice that 'x is not defined in the  
>> toplevel Scheme environment, only in js
>> $5 = #f
>>
>> > (.eval js 'x)  ;; we can get the value of 'x in js using eval  
>> again....
>> $6 = 1
>>
>
> If you want to check whether a symbol is defined in the toplevel  
> then (.isDefined 'foo) works fine.
> You could also use a macro with tryCatch  to test for defined-ness  
> without having to quote the symbol...
>
>> > (tryCatch (begin x #t) (lambda(e) #f))
>> $7 = #f
>>
>> > (define-macro (isDefined s) `(tryCatch (begin ,s #t) (lambda(e)  
>> #f)))
>> $8 = (macro isDefined (s)...)
>>
>> > (isDefined sin)
>> $9 = #t
>>
>> > (isDefined sine)
>> $10 = #f
>
>
> I like the try/Catch approach better because the (.isDefined 'x)  
> relies on the implementation of the Symbol.java class
> in the jsint package, which could conceivably change at some point,  
> whereas the tryCatch approach relies only on
> the syntax of macros and tryCatch and the fact that evaluating an  
> undefined symbol generates an exception....
> But, using (.isDefined 'foo) is ten times faster then the tryCatch  
> approach  ...
>
>>
>> > (time (isDefined foo) 100000)
>> $10 = (#f (2929 msec) (367880 bytes))
>>
>> > (time (.isDefined 'foo) 100000)
>> $11 = (#f (211 msec) (135856 bytes))
>
> Does that help??
>
> Best,
> ---Tim---

Re: [Jscheme-user] Testing if a symbol is bound?

From: Michael T. <mt...@bb...> - 2006-01-11 16:39:56

Hmmm - thanks.  I think I'm going to stick to my definition:
(define (bound? symbol) (.isDefined symbol))
even though performance isn't much of an issue in the cases I want to 
use it.

I guess the followup question ought to be "How do I unbind a symbol?" 
but not only is this a hairier problem, but I don't really require an 
answer... ;-)

Cheers,
    -mik

Timothy J Hickey wrote:

> Hi mik,
>
> On Jan 10, 2006, at 3:10 PM, Michael Thome wrote:
>
>>  What is the "proper" way to test to see if a symbol is bound?
>
> There is no proper way, as far as I can tell.
>
>>
>>  I was expecting something like (bound? 'foo).
>
> If you have created a scheme environment using the jscheme.JScheme 
> constructor,
> then there is an isDefined method which tests whether a symbol is 
> defined in that interpreter,
> e.g.
>
>> [Timothy-Hickeys-Computer:~/Research/Software/jscheme] tim% java -jar 
>> lib/jscheme.jar
>> JScheme 7.2 (1/10/06 8:55 AM) http://jscheme.sourceforge.net
>> > (define js (jscheme.JScheme.))  ;; create a new scheme interpreter
>> $1 = jscheme.JScheme@5db13f
>>
>> > (.eval js '(define x 1))   ;; evaluate a define in that interpreter
>> $2 = 1
>>
>> > (.isDefined js "x")   ;; check to see if the symbol corresponding 
>> to the string "x" is defined in that interpreter
>> $3 = #t
>>
>> > (.isDefined js "y")  ;; notice that "y" is not defined
>> $4 = #f
>>
>> > (.isDefined 'x)  ;; also notice that 'x is not defined in the 
>> toplevel Scheme environment, only in js
>> $5 = #f
>>
>> > (.eval js 'x)  ;; we can get the value of 'x in js using eval 
>> again....
>> $6 = 1
>>
>
> If you want to check whether a symbol is defined in the toplevel then 
> (.isDefined 'foo) works fine.
> You could also use a macro with tryCatch  to test for defined-ness 
> without having to quote the symbol...
>
>> > (tryCatch (begin x #t) (lambda(e) #f))
>> $7 = #f
>>
>> > (define-macro (isDefined s) `(tryCatch (begin ,s #t) (lambda(e) #f)))
>> $8 = (macro isDefined (s)...)
>>
>> > (isDefined sin)
>> $9 = #t
>>
>> > (isDefined sine)
>> $10 = #f
>
>
>
> I like the try/Catch approach better because the (.isDefined 'x) 
> relies on the implementation of the Symbol.java class
> in the jsint package, which could conceivably change at some point, 
> whereas the tryCatch approach relies only on
> the syntax of macros and tryCatch and the fact that evaluating an 
> undefined symbol generates an exception....
> But, using (.isDefined 'foo) is ten times faster then the tryCatch 
> approach  ...
>
>>
>> > (time (isDefined foo) 100000)
>> $10 = (#f (2929 msec) (367880 bytes))
>>
>> > (time (.isDefined 'foo) 100000)
>> $11 = (#f (211 msec) (135856 bytes))
>
>
> Does that help??
>
> Best,
> ---Tim---
>