This page is part of the web mail archives of SRFI 118 from before July 7th, 2015. The new archives for SRFI 118 contain all messages, not just those from before July 7th, 2015.
On 12/20/2014 08:21 AM, John Cowan wrote:
I think this is an excellent SRFI, and I support it. However, it specifies only that `make-string` must return a variable-length string. What about `string`, `string-*case`, `substring`, `string-copy`, and `string-map`?
Well, it does say:Standard Scheme functions that return mutable strings, such as make-string or
string-copy, are specified to return variable-size mutable strings by default.
My notion is that `string` ought to be free to return either a variable-length or a fixed-length string, and that the others ought to be guaranteed to return variable-length strings if (not iff) their string argument is variable-length.
We could do something like that, but is the extra implementation flexibility justified by the extra complexity? There is something to be said for just having two kinds of strings: immutable and mutable variable-sized. If we allow some functions to return fixed-size mutable strings, I think it would be simpler to just specify some functions always return variable-sized strings, and some may return fixed-size mutable strings. In retrospect, it would have been cleaner if functions such as string-upcase or string-append were defined to return immutable strings, but for compatibility they must returns mutable strings, though not necessarily variable-sized ones.
Also, what about conversions between fixed-length and variable-length strings? On Kawa, these would be no-ops, but on other systems they might not be.
If we specify that some functions (for example string-copy) always returns a variable-size string, then we don't need explicit conversion functions: string-copy will do. If we split up the r7rs string functions, I suggest: Procedures that may return a fixed-size string: string string-upcase string-downcase string-foldcase substring string-append list->string (These are functions it would be plausible for a future RnRS to specify that they should return an immutable string.) Procedures that must return a variable-size string: make-string string-copy -- --Per Bothner per@xxxxxxxxxxx http://per.bothner.com/