Re: when to use strings, when to use symbols

[Hans Aberg]

On 9 Jan 2011, at 03:25, Andy Wingo wrote:

> Let's say you have an association list.  It could be (("foo" .  
> "bar")) or
> ((foo . "bar")) or ((foo bar)), or even (("foo" . bar)).  If you're
> parsing this data from over the network, in textual form, which do you
> use?
>
> The answer is this:
>
>  * Use symbols when you want to match against a symbol literal in your
>    source code.
>
>  * Use strings otherwise.

I have found very useful the associative container with keys  
implemented as a balanced tree and called std::map in C++ and Map in  
Haskell. The keys then varies according to context. For example,  
sparse multivariate polynomials can be implemented as a map from  
monomials to coefficients. Then sparse multivariate monomials can be  
implemented as a map from variables to exponents (integers); for  
variables, I choose strings.

> ps. I very, very rarely hold Python up as an example of language  
> design,
> especially regarding strings, but I think that their approach to  
> string
> mutabililty and identity is preferable to the symbol vs string
> distinction that Scheme has.

Symbols and strings are semantically different with respect to the  
lambda theory. Perhaps in Scheme, symbols are used in other contexts  
because 'eq?' is faster, which was important on the slower computers  
of the past.