I implemented something similar when I wrote libs/gap-buffer. It's called
'circular' and wraps an underlying sequence, allowing indexing to start from
any point in the sequence and wrap around.
TUPLE: circular start ;
C: circular ( seq -- circular )
0 over set-circular-start [ set-delegate ] keep ;
: circular@ ( n circular -- n seq )
[ tuck circular-start + swap length mod ] keep delegate ;
M: circular nth ( n seq -- elt ) bounds-check circular@ nth ;
M: circular nth-unsafe ( n seq -- elt ) circular@ nth-unsafe ;
M: circular set-nth ( elt n seq -- ) bounds-check circular@ set-nth ;
M: circular set-nth-unsafe ( elt n seq -- ) circular@ set-nth-unsafe ;
: change-circular-start ( n circular -- )
#! change start to (start + n) mod length
[ circular@ drop ] keep set-circular-start ;
I'm not sure what the problem you're encountering is, but maybe this will
help you work it out.
Alex
On 1/13/07, Daniel Ehrenberg <[EMAIL PROTECTED]> wrote:
Hi all
I'm trying to implement a particular datastructure in Factor for XML
parsing. It's sorta like a circular list. The code is at
http://paste.lisp.org/display/35077 . For some reason, it works when I
use things like length, nth and set-nth, but >string and sequence=
don't work, complaining that there is no length method. Strangely,
each and map still do work. Do you have any ideas for how to fix this
or what the problem is? Chris thought it might be something related to
delegation, but that isn't true, because no delegation is used. He
said that the code actually works if you step through nth-unsafe in
the walker. Is there an error in what I've written, or possibly in the
implementation of generic words?
Dan
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