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Date:Mon Jan 25 18:43:14 1993 
Subject:Folding in VED 
From: Robin Popplestone  
Volume-ID:930126.06 

> Before this glorious future arrives, there is one feature I would love
> to have incorporated into VED as soon as possible -- and that's
> folding.  I'm always frustrated that when I'm writing a large program
> I can't collapse a bunch of related functions togther into a single
> line.  I thinking that text "folding" (as in the original OCCAM editor)
> could well add something special to VED.

It is always a mistake to pronounce something "hard". But it seems to
me that there is a real problem here, namely the mapping between screen
space and buffer-space. In VED (unlike EMACS) a buffer is conceptually
2-dimensional (EMACS has a 1-dimensional model of a buffer as a string,
which is no doubt optimised behind-the-scenes). Thus the mapping from
buffer space to screen space in VED is a linear transform (if you play the
old projective-geometry hack of homogeneous coordinates). This is deeply
built into VED. Folding would of course change the mapping.

Similar probems arise with a system like Pantechnicon. Here, each logical
sub-unit has an associated size, and the mapping from buffer-space to
screen-space requires a recursive descent through the hierarchy (do-able in
log time if there is a bound on the tree-branching-ration).

Robin