Re: string->symbol escaping numbers

Hello Lorry,

the symbol is escaped to distinguish it from a number! Note that both symbols and numbers are atoms, but numbers are not symbols, nor vice versa:

  (atom? 3) ;=> #t
  (atom? '|3|) ;=> #t
  (symbol? 3) ;=> #f
  (symbol? '|3|) ;=> #t
  (number? 3) ;=> #t
  (number? '|3|) ;=> #f

  (memv 3 '(foo 3)) ;=> '(3)
  (memv '|3| '(foo 3)) ;=> #f

  (memv 3 '(foo |3|)) ;=> #f
  (memv '|3| '(foo |3|)) ;=> '(|3|)

Ciao,
Thomas

19.07.2024 12:44:58 Lawrence Woodman <[email protected]>:

> Hello,
> 
> I'm confused by string->symbol escaping the symbol when used with a string
> consisting soley of a number:
> 
> (string->symbol "3")  =>  |3|
> (eq? (string->symbol "3") 3)  =>  #f
> 
> I've looked but can't find a reason for its being escaped.  It would be
> great if someone could explain or point my in the direction of
> somewhere that explains what is happening here.
> 
> The reason this is important to me is because I want to use memq in a
> cond to handle various inputs a bit like this with itemtype as a symbol:
> 
>     (cond ((memq itemtype '(text 0))
>             (list "0" username selector hostname port))
>           ((memq itemtype '(menu 1))
>             (list "1" username selector hostname port))
>           ((memq itemtype '(error 3))
>             (list "3" username selector hostname port)))
>          
> There are workarounds I could make such as comparing against strings but
> ideally I would like to pass itemtype around as a symbol.  Is there an
> idiomatic way of handling this situtation?
> 
> 
> Best wishes
> 
> 
> Lorry