[erlang-questions] Reading comments/annotations inside parse_transforms

Tim Watson <>
Tue Jul 10 19:20:39 CEST 2012

Does anyone have any suggestions about this, or do I just resort to brute force to get it done?

On 5 Jul 2012, at 10:10, Tim Watson <> wrote:

> There doesn't appear to be any way of doing this currently. There is
> support in erl_syntax for working with these and there is also an
> erl_comment_scan module in the syntax-tools application which parses
> and returns comments from a file (or whatever). What there doesn't
> appear to be, is a means to get erl_parse to return comments as
> attributes (?) in the AST that the compiler passes to a
> parse_transform.
> My question then, is this: what is the best (only!?) way to process
> comments at the same time as source code in a parse_transform? So far,
> given that this seems unlikely to work OOTB, I'm assuming I'll have to
> do something like:
> 1. once you hit the 'file' attribute, parse the comments and stash
> these away in a useful place
> 2. process the forms as usual, comparing each line number for each
> form, against the line numbers stored for the comments
> 3. when you get an interleaving of code and comments, you know where
> the comments reside in the source file in relation to the form you're
> currently working with
> I *can* do this of course, but it seems like an awful lot of hard
> work. Why can't comments be preserved in the AST passed to a parse
> transform, and then just dropped later on!? Is there an easier way of
> doing this that I'm currently missing?
> Cheers,
> Tim

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