OpenEuphoria

Re: On indexes

• Posted by christian.cuvier at education.gouv.fr Aug 23, 2002
• 400 views

Thank you very much.
    So we are probably in the case where a major feature of the language is
stated in an end note buried in the docs. Deserves better IMO.

Regards.

Chris

----- Original Message -----
From: "Matthew Lewis" <matthewwalkerlewis at YAHOO.COM>
To: "EUforum" <EUforum at topica.com>
Subject: RE: On indexes


>
>
> -----Original Message-----
> From: christian.cuvier at education.gouv.fr
> [mailto:christian.cuvier at education.gouv.fr]
>
> > But there may be a problem with variable depth indexing. Assume we want
to
> manipulate
> > arbitrary trees in Euphoria. Trees are two-terms sequences: one object
as
> root node
> > content and a sequence of 0 or more trees (the subtrees originating from
> root).
>
> > Accessing an individual statement using ordinary indexes requires to
know,
> before run
> > time, its depth. Since generally we don't, the indexing scheme should be
> dynamic, so
> > it must be a sequence. How to get or set an arbitrary tree subtree or
> element (a 0-depth
> > node), given a tree, an index sequence and a value?
>
> > What about setting an element?
> > The way I found is to duplicate the tree with the modified element and
> return it. It seems
> > a terrible waste of machine cycles and memory. If somebody knows better,
> I'd appreciate.
> > If the interpreter is so smart that it does not really duplicate the
> structure, this rare
> > feature needs be more thoroughly documented.
>
> This came up a while back.  After some help from Jiri, I came up with the
> following iterative fetch and recursive store functions.  It should only
> copy the most deeply nested sequence within b.  Mostly, only pointers are
> copied (internally).  Pass c = 0 to simply assign b = a.  c = {1,0} = {1}.
> I use this in my database code to fetch and store nested fields.
>
> -- return a[b...]
> function seq_fetch(object a, sequence b)
>
>     for i = 1 to length(b) do
>
>         a = a[b[i]]
>
>     end for
>
>     return a
> end function
>
> -- store a in b at subcript c
> function seq_store(object a, object b, object c)
>     integer len
>
>     if atom(c) then
>         c = {c}
>     end if
>
>     len = length(c)
>
>     -- now it will insert a new element!
>     if c[1] = -1 or length(b) + 1 = c[1] then
>         return b & { a }
>     elsif len > 1 then
>         -- recursively go into the sequence
>
>         b[c[1]] = seq_store(a, b[c[1]], c[2..len] )
>         return b
>     end if
>
>     -- get the index
>     c = c[1]
>
>     if c then
>         b[c] = a
>     else
>         b = a
>     end if
>
>     return b
> end function
>
>
> Matt Lewis
>
>
>
>