[erlang-questions] erl_scan, erl_parse, macros and records

[Mihai Balea]

On Jun 16, 2011, at 3:48 PM, Dan Kelley wrote:

> 
> Hi,
> 
> I'm working on a router of sorts.  I'd like to have a config file which specifies how to classify messages, what channels are available, and routing rules based on classifications and channels.
> 
> When my application starts, I'd like to transform the configuration into a module (let's call it 'router') so I can do someting like 'router:route(Message)'.  Message will be a record that encapsulates a bunch of things about the message, and the returned value will be the channel to which the message should be delivered.  The Message record is reasonably complicated - the top level thing contains several layers of different records.  I also have a large number of macros that I use to extract different fields/subrecords of a top-level Message.
> 
> When I started looking at how to do this, I quickly found erl_scan, erl_parse, and friends.  I can easily create a module on the fly with these, but everything falls apart when I need to get at the Message record and macro definitions.  Despite the access provided to compiler-ish things by erl_scan, erl_parse and friends, it looks like the only way to get at the preprocessor is to use epp on files.  This is a problem because the code I want to dynamically create needs to use the record definitions and macros from the Message header file.
> 
> Trying to figure a way around this led me to aleppo, which neatly solved the problem of including the header file, but aleppo doesn't process records.  For a brief and exciting moment, it looked like erl_expand_records might save the day, but it expects forms, and I can't get anything with records through erl_parse:parse_form.
> 
> Am I missing an easier way to dynamically create code that references macros and records?
> 
> Thanks,

Why not generate a temporary file and apply compile:file/2 on it? 

Mihai