On Thu, May 25, 2006 at 12:23:51AM -0700, j h woodyatt wrote:
> On May 24, 2006, at 10:56 PM, Martin Jambon wrote:
> >
> >So I'd really love to see actual examples where using immutable  
> >strings would be such an improvement over mutable strings.
> >If the problem is just to ensure that string data won't be changed  
> >by the user of a library, then it is trivial using module  
> >signatures and String.copy for the conversions.
> 
> I have no dog in this fight, but I can imagine a pragmatic approach  
> that might satisfy some of these concerns without introducing much in  
> the way of extra runtime complexity costs.
> 
> Change the way strings are boxed so that there is an additional tag  
> for immutable strings as opposed to the normal mutable ones.  In all  
> respects, allow string objects with either tag to be treated the same  
> by functions that do not modify the content of the string.  When the  
> "safe" variants of the string mutation functions are called on a  
> string object with the immutable tag, throw a runtime exception.   
[...]

Compiletime error would be what I would prefer.


[...]
> It *might*  
> give a pragmatic benefit of surfacing unintentional programming  
> errors earlier than they might otherwise be found,
[...]

The earlier the better it is.
It's like non-matching types found by the compiler: it helps
a lot in development. Debugging normallay takes the most time
in development; and with OCaml debugging time decreases much - that
is what I experienced. And this comes from early getting a hint
to possible problems (possible with compilers that would accept
such code; im possible when the compiler says: "no! I don't accept
these sources!").

Ciao,
  Oliver