Testing for Pre-existing symbols in a context

[Tim Johnson]

Example:

I have written my own cgi context. It has a number of control

variables (think symbols)

I want to - if necessary customize those symbols on startup.

I have a context method call 'on.

Code Select Expand


;; Intialize the CGI object
(cgi:on 'cs nil 'placeholder true) ;; assumes that 'cs and 'placholder
                                              ;; are already defined

Inside of the 'on method, a helper function called 'parse-args

intercepts args and processes them two at a time as follows:

Code Select Expand


(define (parse-args)
 (let((key)(val))
   (dolist (item (explode (args)))
  (set 'key (last(parse(string(first(first item)))":")))
  (set 'val(second(first item)))
  (set (sym key) val))) ;; reset the symbol
 )
As written, I may mistakenly submit a symbol that is not predefined

in the context. I would like to be able to test whether that symbol

is already defined and throw an error if not. I like error messages!

I'd welcome some suggestions on how to proceed.

Thanks

Tim

[lithper]

"symbols"



> (context 'cgi 'xxx 33)

33

> xxx

nil

> cgi:xxx

33

> (symbols cgi)

(cgi:xxx)

>

[cormullion]

Is symbol? useful here?



(symbol? exp)

Evaluates the exp expression and returns true if the value is a symbol; otherwise, it returns nil.

[Jeff]

(context? ctx "symbol")

[Tim Johnson]

(context? ctx "symbol")

Hello Jeff:

A quick test suggests that this is what I'm after.

Thanks

Tim