[Python-Dev] The impact of '@' on Leo (original) (raw)
Edward K. Ream edreamleo at charter.net
Fri Aug 6 00:09:32 CEST 2004
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> 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.
Can you give an example of a file that would be difficult to understand under that change? If you allow @foo inside a Python file, it is not Python anymore, is it?
There are two files involved. The .leo file (an xml file) contains the "marked up" code. Leo turns this file into a visual outline containing zero or more "derived files" that could be written in any language.
Here is the entire top-level node in the outline that represents the derived file leoApp.py:
[Node starts]
@first # -- coding: utf-8 --
@language python @tabwidth -4
import leoGlobals as g import os import sys
class LeoApp:
"""A class representing the Leo application itself.
Ivars of this class are Leo's global variables."""
@others[Node ends]
- The [Node starts] and [Node ends] are not part of the node, they delimit the node in this email.
- The @first directive makes sure that the first line of leoApp.py is # -- coding: utf-8 --
- The @language python and @tabwidth directives tell Leo how to syntax color the text and how to handle tabs.
- The @others directive tells Leo to insert all descendent nodes. In this case, each descendent node contains a single method of the LeoApp class.
- There are other details to Leo's markup, but this gives you the general feel.
Everything else is plain Python. When saving the .leo file, Leo produces leoApp.py following the rules of the markup. In particular, Leo writes all descendent nodes in place of the @others directive, indented the same as the @others directive. Most of these descendent nodes will contain few or no Leo directives: descendent nodes inherit most directives from their ancestors.
The problem is that Leo doesn't really understand any language, except to colorize it. Most Leo directives must start with @ in the leftmost column, but the @others and @all directives may contain leading whitespace. If @foo is both a valid Python construct and a valid Leo directive Leo will treat @foo as a Leo directive even if it is "supposed" to be Python.
If @foo is not a valid Leo directive, Leo creates a "verbatim" sentinel line in the derived file to indicate that the next line isn't a directive, even though it sorta looks like one. Like this:
#@verbatim @foo
This is basically how Leo handle's languages with @ signs. There is no problem until @x in the language conflicts with a Leo directive, in which case Leo doesn't have any way of distinguishing which usage was intended.
As I said in another post, Leo doesn't have escape conventions involving @ signs, and that has turned out well. There have been requests to allow strings other than "@" to delimit Leo directives, and that will probably happen, but in general Leo really would rather stick to "@"
Edward
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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