Re: Guile: What's wrong with this?

[nalaginrut <nalaginrut@gmail.com>]

> >   In many systems it is desirable for constants (i.e. the values of literal
> >   expressions) to reside in read-only-memory.  To express this, it is
> >   convenient to imagine that every object that denotes locations is
> >   associated with a flag telling whether that object is mutable or immutable.
> >   In such systems literal constants and the strings returned by
> >   `symbol->string' are immutable objects, while all objects created by
> >   the other procedures listed in this report are mutable.  It is an error
> >   to attempt to store a new value into a location that is denoted by an
> >   immutable object.
> > 
> > In Guile this has been the case since commit
> > 190d4b0d93599e5b58e773dc6375054c3a6e3dbf.
> > 
> > The reason for this is that Guile’s compiler tries hard to avoid
> > duplicating constants in the output bytecode.  Thus, modifying a
> > constant would actually change all other occurrences of that constant in
> > the code, making it a non-constant.  ;-)
> 
> This is a terrible example of the RnRS promoting some strange idea of
> mathematical purity over being useful.
>  
> The idea that the correct way to initialize a string is
> (define x (string-copy "string")) is awkward.  "string" is a read-only
> but copying it makes it modifyiable?  Copying implies mutability?
>  
> Copying doesn't imply modifying mutability in any other data type.
>  
> Why not change the behavior 'define' to be (define y (substring str 0)) when STR
> is a read-only string?  This would preserve the shared memory if the variable is never
> modified but still make the string copy-on-write.
>  
> Regards,
>  
> Mike
> 

Hi guys! I just pass by and see your dispute.
I have been confused by the new immutable string design. But I used a
macro "make-mutable-string" which hide string-copy for an abstraction.
Anyway, if the efficiency would be an issue, one may choose bytevector
to implement "make-mutable-string". And it's easy to substitute with
sed.

BTW, can't we make an efficient "mutable-string" module for an
alternative? Just like old version. I mean it could be a Guile specific
feature.

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