Re: [ jEdit-devel ] Parser generator to use in a jEdit plugin

[Lucas D. <ld...@in...>]

Shlomy Reinstein wrote:
> Thanks for the input. Note that my usage of parser generators is for a
> completely different purpose.
> As you know, syntax highlighting and indentation in jedit are
> specified using special-syntax "mode files", and are handled in a very
> complex way inside the core. Replacing these with a generated parser
> requires changing about half of jEdit...

I was more thinking of ways to compile more general grammars into the
internal machinery of jEdit (which I know very little about). The
current mode-language is not expressive enough to describe the syntax of
languages I work with (Standard ML mostly). I'm not sure if this is a
limit of the internal machinery of jEdit, or if it is just a limit of
the mode language. This is something I've been meaning to figure out for
a while, but not quite got round to.

> A long time ago I used to think that all editors that offer syntax
> highlighting use some grammar files for specifying the grammar of each
> mode. I was very surprised (a long time ago) to find that this is not
> the case, and in fact each editor has its own custom way of specifying
> how to syntax highlight the text and how to auto-indent.
> 
> It took me a while to realize that using a generated parser is not
> good enough due to the limitations of such grammars. You cannot parse
> a small part of the code (e.g. a single modified line) and update the
> data structures accordingly, which is what an editor does on each
> change of the text. jEdit maintains the token & parse information of
> each line in some cache, and its sophisticated rule handling only
> needs to do little work each time (most of the time). Parsing the
> entire text of the buffer on each change is not acceptable
> (performance wise), though maybe some time in the future it will be
> acceptable...
> 
> I am not very familiar with the syntax coloring and indentation in
> jEdit, but I'll be glad to share what I do know.

Thanks, even that high level view is useful to me. :) I also was naively
thinking that general purpose grammars should work out - perhaps
interestingly, I've done a little work on composable grammars - this
machinery was intended to work with a general grammar's parse tree, so
that is can be updated from text anywhere in the string, rather than
just at the start - also aiming for text which be edited anywhere and
for the parse tree to be updated in a minimal fashion. I should write
that up... and maybe also read more about other approaches - any
suggested reading?

In the meantime, is there is a way to write a mode purely in java,
without going through the compilation machinery of a mode file, so that
I might have a look at writing my own special syntax highlighter and
indentation? I guess I'm wondering what events the syntax highlighter
has to respond to, and similarly for indentation, and what functions I
might be able to re-use to simply tell jedit what colour to use for what
chunks of text...

as I write this, I'm starting to think this might be a lot of work...

any suggestions and comments would be very welcome,

best,
lucas

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