[erlang-questions] in-flight module transforms - request for comments

Ulf Wiger <>
Tue Oct 18 13:12:40 CEST 2011


On 18 Oct 2011, at 12:06, Ulf Wiger wrote:

> From those of you who enjoy modifying existing code at run-time, I would like to ask for some input.
> 
> Inspired by Joe Norton's use of Meck to introduce support for asciiedoc syntax in EDoc [1], I started playing with Meck to do similar things with e.g. tweaking epp on the fly for alternative syntax support.

So, just to illustrate what tweaking epp could look like:

Say I want to abbreviate the Erlang fun … end syntax, using something shorter:

-module(toker_test).
-export([double/1, i2l/1]).

double(L) ->
    lists:map(`(X) -> X*2`, L).

i2l(L) ->
    lists:map(`integer_to_list/1, L).

A sample shell dialogue:

Eshell V5.8.4  (abort with ^G)
1> c(toker_test,[{outdir,"../ebin"}]).
./toker_test.erl:5: syntax error before: '`'
./toker_test.erl:8: syntax error before: '`'
./toker_test.erl:2: function double/1 undefined
./toker_test.erl:2: function i2l/1 undefined
error
2> c(toker_c,[{outdir,"../ebin"}]).   
{ok,toker_c}
3> toker_c:c(toker_test,[{outdir,"../ebin"}]).
{ok,toker_test}
4> toker_test:double([1,2,3]).
[2,4,6]
5> toker_test:i2l([1,2,3]).
["1","2","3"]

The actual tweak is almost exactly like the example I showed earlier, but replacing epp:parse_erl_form/1 with a version that calls my own, modified version of erl_parse. The other thing needed is to export epp:epp_request/2.

Not that I'm recommending doing this for real!  ;-)

BR,
Ulf W

Ulf Wiger, CTO, Erlang Solutions, Ltd.
http://erlang-solutions.com






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