k32 / erlang_qq

Simple Erlang quasiquotation/splicing parse transform

erlang_qq

A simple quasi-quotation parse transform for Erlang (extracted from typerefl library).

It’s dumb and inefficient, but it’s only used to help creating parser transforms, so hopefully it’s not used often enough to impact compilation time.

How to use it:

• =’$$’(…)= pseudo-function quotes its argument.
• =’$’(…)= pseudo-function inside =’$$’= unquotes its argument.
• Content of variables with __AST suffix is spliced in unquoted
• =’$const(…)’= pseudo-function returns the AST of an erlang term corresponding to the argument

-compile({parse_transform, erlang_qq}).

...

create_form(Line, Default__AST) ->
  %% Quote some code
  '$$'(begin
         Foo = case some_module:function() of
                 {ok, Result} -> Result;
                 undefined    -> Default__AST %% Here AST is spliced as is
               end,
         '$'(other_form('Foo')) %% Argument is executed and spliced in as is, unquoted
       end).

other_form(Line, Var) ->
  {var, Line, Var}.

Known issues: code locations in the transformed code may be incorrect in some cases.