Re: [code] Debugging language modules

From: Mitchell <>
Date: Sat, 26 Mar 2016 14:28:05 -0400 (EDT)

Hi Arnel,

On Sat, 26 Mar 2016, Arnel wrote:

> Hello,
> I am currently working on a language module for Racket (formerly PLT Scheme).
> Here are the questions I have:
> - I have the following lines in the 'init.lua' file for the Racket module:
> textadept.file_types.extensions.rkt = 'racket'
> [snip]
> However, if I open a Racket script and try testing the syntax checking, nothing
> happens. The 'init.lua' file is located inside the 'racket' directory inside
> '~/.textadept/modules'. If I run
> ui.print(textadept.file_types.extensions.rkt)
> from the command entry, I come up with plain 'nil'. Why is that?

This is a bit of a Catch-22. I've snipped the relevant line from your
Racket module's init.lua file. In order for Textadept to know the 'rkt'
extension should load the 'racket' lexer (and eventually the 'racket'
module), that line needs to be run earlier. Right now, you are expecting
Textadept to load the 'racket' module, which then tells Textadept about
the extension needed in order to load the 'racket' module... Put that
single line in your `~/.textadept/init.lua` file and everything will work
as expected.

> If I place these lines in my regular '~/.textadept/init.lua', the syntax
> checking works fine.

This illustrates my point above :)

> - Is there a better way to debug lexer modules? The Racket lexer I'm working on
> was based off the Scheme lexer file provided with TA. I've read somewhere in
> the API manual that troubleshooting lexers can be tricky and it's recommended
> to run TA in the terminal to get the error messages. I tried this but I didn't
> get any. Those who have written lexers for other languages before - any
> pointers? Anything on seeing what's actually captured by the LPEG expressions
> would be great.

If you don't see any error messages in the terminal by default, then that
means your lexer is well formed and is processing text just fine. However,
that doesn't mean your lexer is processing text as you'd expect! Robert
already mentioned using Scintillua as a library (which is an idea I hadn't
thought of!). Normally I just use:

   P(function(input, index)
     return index

and put that in a pattern I'm debugging. The "return index" line ensures
that debug function "matches" so that text matching can continue.


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Received on Sat 26 Mar 2016 - 14:28:05 EDT

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