merl vs erl_syntax

Hugo Mills hugo@REDACTED
Fri Feb 25 22:19:34 CET 2022

   I'm trying to write some code that compiles a small DSL into erlang
functions. I found the merl module, but that doesn't seem to have a
function to output its AST to a file. So I tried writing the AST with
erl_prettypr:format/2, but it fails.

The code I'm using to generate this example is:

        MapperName = 'foo',
        Mapper = ?Q("@MapperName(Row) -> Row."),
        io:format("~p~n", [Mapper]),
        io:format("~ts", [erl_prettypr:format(Mapper, [{encoding, utf8}])]),

The first io:format/2 in the above code results in this output:


The second io:format/2 results in this:

erl_syntax:type failed on line 734
Reason: {badarg,foo}

=== Ended at 2022-02-24 18:31:54
=== Location: [{erl_syntax,type,734},
=== === Reason: bad argument: foo
  in function  erl_syntax:type/1 (erl_syntax.erl, line 734)
  in call from erl_prettypr:lay_2/2 (erl_prettypr.erl, line 450)
  in call from erl_prettypr:lay_2/2 (erl_prettypr.erl, line 605)
  in call from erl_prettypr:format/2 (erl_prettypr.erl, line 288)
  in call from stad_compile:compile_relalg/1 (src/stad_compile.erl, line 11)
  in call from compile_SUITE:rename/1 (test/compile_SUITE.erl, line 10)
  in call from test_server:ts_tc/3 (test_server.erl, line 1783)
  in call from test_server:run_test_case_eval1/6 (test_server.erl, line 1292)

If I put the same function ("foo(Row) -> Row.") into a module, and use
epp:parse_file/3 to read it, I get this fragment of the output:


   Note that this output has {tree,atom,_,foo} as the function name,
where the merl output has simply foo. This suggests to me that merl
isn't generating the same kind of AST as epp. Are these things
actually incompatible?  Are they intended (or just known) to be so?

   What libraries and techniques would people recommend that I use to
generate erlang code?


Hugo Mills             | PowerPoint is just graphic novels for business
hugo@REDACTED | meetings.  |
PGP: E2AB1DE4          |                                             @zer0jack

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