# erlang_qq

**Repository Path**: porter4code/erlang_qq

## Basic Information

- **Project Name**: erlang_qq
- **Description**: No description available
- **Primary Language**: Erlang
- **License**: Apache-2.0
- **Default Branch**: main
- **Homepage**: None
- **GVP Project**: No

## Statistics

- **Stars**: 0
- **Forks**: 0
- **Created**: 2025-04-18
- **Last Updated**: 2025-04-18

## Categories & Tags

**Categories**: Uncategorized

**Tags**: None

## README

#+TITLE: 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

#+begin_src erlang
-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}.
#+end_src

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