[Python-Dev] The impact of '@' on Leo

[Edward K. Ream]

The mandate for this post is the following from GvR:

> Please bring up the Leo issues in Python-dev.

The major concern I have with '@' syntax as it relates to Leo is the
potential for ongoing and never-ending conflicts between Leo's directives
and @x constructs in Python.

Leo presently supports the following directives:

@ (followed by one or more whitespace characters)
@all, @asis,
@c, @code, @color, @comment,
@delims, @doc,
@encoding, @end_raw,
@file, @first,
@header,
@ignore,
@killcolor,
@language, @last, @lineending,
@nocolor, @noheader, @noref, @nosent, @nowrap,
@others,
@pagewidth, @path,
@quiet,
@raw,
@root, @root-code, @root-doc,
@silent,
@tabwidth, @terse, @thin,
@unit,
@verbose,
@wrap

Worse, Leo allows plugins to define their own directives.  There is already
a plugin that defines @wiki.  Furthermore, @run, @test and @suite are also
used in special contexts.

Leo's users could probably live with a small, fixed set of @x constructs in
Python.  But if the Python programmer can create new @x identifiers then
they have a big, big problem.  What happens when another Python @x construct
conflicts with one of these directives or some other directive?

These directives act as a markup meta-language.  Many of these directives
are found interspersed in the code: a conflict with a construct in Python
would have most unhappy consequences.

To make matters worse, one of the _best_ choices I ever made in Leo was to
remove all "escape" conventions regarding '@' (and other noweb constructs).
This took a bit of courage, but it has turned out to be clearly the right
choice.  But if Python can now generate arbitrary @x strings Leo will have
to do something really drastic.

There are a number of markup languages that use '@' to from the underlying
language (Python) to the markup language.  I was always under the impression
that the clear statement in the Reference Manual that at signs are invalid
everywhere (except in comments and strings) was a clear signal of an
intention to keep those symbols for other valid purposes.  I do hope this
won't change.

Edward

P.S.  I recently wrote a pretty-printer for Python using the tokenize
module.  What will be the status of the '@' token?  Is it still an
"errortoken" ?  Sure, this is a minor point, but it _will_ affect other
tools.

EKR
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Edward K. Ream   email:  edreamleo at charter.net
Leo: Literate Editor with Outlines
Leo: http://webpages.charter.net/edreamleo/front.html
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