On 2/24/20 2:00 PM, Shiro Kawai wrote:
> Literal empty string is immutable, off course.  What I meant by "empty string" is something that's returned from (string-copy "abc" 0 0) or even, (string-copy "").

I'm not sure what you're asking or who you're asking.

In srfi-140, (string-copy "") returns an fresh zero-length mutable string.
This is a valid argument to string-append! and string-replace!.
It is not an "empty string" in the R7RS "3.4 storage model" sense.

The following is valid:

     (define w (string-copy ""))
     (string-append! w "abc")
     (string-append! w "xyz")

Also note (not explicitly specified by srfi-140, but I think implied):

     (define s1 (string-copy "))
     (define s2 (string-copy s1))
     (eqv? s1 s2) => #f
     (eqv? s1 "") => #f

I don't think the R7RS concept of a string as consisting of a location
per character is appropriate.  Better to view a string as a single location.
Literal strings or other istrings that are equal? may be combined
into a single location, at the discretion of the implementation,
but every mstring must be a unique location.

(In fact, I don't see how the idea of a vector or a pair as consisting of
multiple locations gets you anything useful.  The definition of eqv? in 6.1
talks about them having a single location.)
--
	--Per Bothner
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