Takashi Kato scripsit:

> I've just noticed there is no string-cursor? predicate. Since the SRFI
> adds cursor type, I think it's better to have a predicate for it. Or
> is there a reason why it's not there?

Cursors don't necessarily belong to a disjoint type.  In Chibi they do,
but they could also be implemented as negative exact integers or by some
other means.

I thought of having a predicate (valid-string-cursor? s c) that returns
#t iff c is a valid cursor for s, but it might need to be O(n) in the
length of s, which is not what you expect from a type predicate.

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John Cowan          http://www.ccil.org/~cowan        xxxxxx@ccil.org
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