Re: Question about how to check a symbol is bound

[Kon Lovett]

> On Jun 22, 2023, at 9:07 PM, Pan Xie <xiepan@skyguard.com.cn> wrote:
> 
> Hello
> 
> I am new to CHICKEN scheme and here is a (very) quick question of how to 
> check whether a symbol is bound.
> 
> I know it doable but I can't find the way.
> 
> I don't find the methods from the main CHICKEN manual document. Then I import 
> the "symbol-value-utils" module. I believe the "unbound?" or "symbol-value" 
> will do what I want, but to my surprise they does NOT:
> 
> I expect `symbol-value' will give me value of a symbol, but it will throw 
> exception for an
> undefined symbol, even I provide the default value:
> 
> (symbol-value foo #f)
> Error: unbound variable: foo

#;2> (symbol-value 'foo #f)
#f

(symbol-value foo #f) is asking for the symbol-value of the derefed variable 
`foo’

> 
> I expect (symbol-value (string->symbol "list")) will give me the list 
> procedure, but what I get is '#f'
> 
> (symbol-value (string->symbol "list"))
> #f

#;6> (symbol-value (string->symbol (string-append "scheme" "#" "list")))
#<procedure (scheme#list . lst)>

> 
> I expect (unbound? foo) will return True value, but it just throw exception.

#;7> (unbound? ‘foo)
#t

#;9> (unbound? (string->symbol (string-append "scheme" "#" "list")))
#f

> 
> Does CHICKEN scheme provide facilities that make user check whether arbitrary 
> symbol is bound or get its value, just like the `boundp' or `symbol-value' in 
> Common Lisp?
> 
> Thanks
> Pan
> 
>