Re: shared-substrings missing in 1.7

[Greg Troxel]

Tom's arguments and Roland's explanation of what he is doing are very
persuasive, so I withdraw my comments that removing
make-shared-substring is a reasonable change.

I think Tom's comments about having an explict cross-mutation
semantics for make-shared-substring and having 'make-substring' just
share implementation but not semantics (hence cow).

While I am awed by the whole guardian and weak ref scheme, it might
make sense to just have strings have a refcount (of other scheme
objects that point to their storage), possibly splitting 'string
storage' and 'string object'; the former doesn't even need to be a
scheme object, just length, pointer, and refcount.

It would be cool to enable shortening up the storage if the really big
string is gone, but some smaller ones remain.  But this gets into
searching for references and computing what can go, or having
references be per-character with some sparse/range encoding, and that
sounds too hairy.


-- 
        Greg Troxel <address@hidden>