> > 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. -- GNU Powered it GPL Protected it GOD Blessed it HFG - NalaGinrut --hacker key-- v4sw7CUSMhw6ln6pr8OSFck4ma9u8MLSOFw3WDXGm7g/l8Li6e7t4TNGSb8AGORTDLMen6g6RASZOGCHPa28s1MIr4p-x hackerkey.com ---end key---
