This document summarizes a talk on abusing the Erlang compilation pipeline for fun and profit. It discusses how understanding the different stages of compilation, from source code to BEAM files, allows for optimizations, syntax sugar, language implementations, and more. Key stages discussed include preprocessing, Core Erlang, kernel Erlang, BEAM assembly, and the final BEAM file. Understanding the pipeline provides opportunities for hot code reloading, DSLs, configuration files, and code analysis tools.

1. Abusing Erlang Compilation Pipeline
for Fun and Profit
Erlang UG - Cracow (13.03.2017)

2. ~ # whoami (afronski)
➔ Software and Operations Engineer
at Appliscale
Erlang, Python, JS, AWS, Linux
➔ Co-organizer:
Functional Miners
Silesian BEAMers

4. http://learnyousomeerlang.com/designing-a-concurrent-application#hot-code-loving

5. Brainfuck?
++++++++++[>+++++++>++++++++++>+++>+<<<<-]>++.>+.+++++++..+++.>++.<<+++++
++++++++++.>.+++.------.--------.>+.>.

6. Brainfuck!
8 symbols
+ -
< >
[ ]
, .

7. Brainfuck!
Example:
,----------
[----------------------.
,----------]
a = 97 A = 65
n = 10 a - A = 32

8. github.com/afronski/bferl
+[,+[-[>+>+<<-]>[<+>-]+>>++++++++[<-------->-]<-[<[-]>>>+[<+<+>>-]<[>+<-]<[<++>>>+[<+<->>-]<[>+<-]]>[<]<]>>[-]<<<[[-]<[>>+>+<<<-]>>
[<<+>>-]>>++++++++[<-------->-]<->>++++[<++++++++>-]<-<[>>>+<<[>+>[-]<<-]>[<+>-]>[<<<<<+>>>>++++[<++++++++>-]>-]<<-<-]>[<<<<[-]>>>>
[<<<<->>>>-]]<<++++[<<++++++++>>-]<<-[>>+>+<<<-]>>[<<+>>-]+>>+++++[<----->-]<-[<[-]>>>+[<+<->>-]<[>+<-]<[<++>>>+[<+<+>>-]<[>+<-]]>[
<]<]>>[-]<<<[[-]<<[>>+>+<<<-]>>[<<+>>-]+>------------[<[-]>>>+[<+<->>-]<[>+<-]<[<++>>>+[<+<+>>-]<[>+<-]]>[<]<]>>[-]<<<<<-----------
-->>[[-]+++++[<<+++++>>-]<<+>>]<[>++++[<<++++++++>>-]<-]>]<[-]++++++++[<++++++++>-]<+>]<.[-]+>>+<]>[[-]<]<]
Demo

10. Source Code
% -*- coding: utf8 -*-
-module(main).
-export([main/0, a/0]).
-define(GUESS_WAT, ok).
a() -> ?GUESS_WAT.
main() ->
a(),
io:format("Hello, world!~n").

11. Preprocessor
-file("main.erl", 1).
-module(main).
-export([main/0,a/0]).
a() -> ok.
main() ->
a(),
io:format("Hello, world!~n").

12. sys_pre_expand
-file("main.erl", 1).
a() -> ok.
main() -> a(),
io:format("Hello, world!~n").
module_info() -> erlang:get_module_info(main).
module_info(X) -> erlang:get_module_info(main, X).

13. Core Erlang
Intermediate representation of Erlang, intended
to lie at a level between source code and the
intermediate code typically found in compilers.

14. Core Erlang
During its evolution, the syntax has become
complicated, making it difficult to develop
programs that operate on the source.

15. Core Erlang
module 'main' ['a'/0,'main'/0, ...]
attributes []
...
'main'/0 =
...
apply 'a'/0 ()
call 'io':'format' ([72|[101|[108|[...]]]])
...
end

16. Kernel Erlang
Source Code
module 'main'
export ['a'/0,'main'/0,...]
fdef 'main'/0() =
do
call (local 'a'/0)() >> <>
then
enter (remote 'io':'format'/1)("Hello,
world!~n")

17. BEAM assembler
{module, main}.
{exports, [{a,0},{main,0},...]}.
{function, main, 0, 4}.
{label,4}.
{allocate,0,0}.
{call,0,{f,2}}.
{move,{literal,"Hello, world!~n"},{x,0}}.
...
{call_ext_last,1,{extfunc,io,format,1},0}.

18. BEAM file
464f52310000023c4245414d41746f6d000000
3b00000008046d61696e0161026f6b02696f06
666f726d61740b6d6f64756c655f696e666f06
65726.................................

19. What did I miss?
Parse Transforms
Custom Parsers

20. github.com/afronski/bferl/Compiler
Lexer Parser CodeGen
+++++++++
+[>++++++
+>
Core
Erlang

21. Tools
- Leex and Yecc
- cerl:*, cerl_clauses:*
- c(example, to_core).
- Erlang playground
- It allows to compile source into different forms.
- Interactively!

22. Okay, we know how to “abuse” it. ;)
But why?

23. Community
Examples

24. Hot-Code Reloading
Configuration as a Code
Hardwiring Dependencies in Code

25. DSL
Templating Engines
Configuration Files
Elixir EEx

26. Different Languages
LFE
Elixir
Typed Erlang

27. Syntax Analysis and
Transformations
Mutation Testing
Code Analysis Tools
Syntax Sugar ;)

28. Low-level
Optimizations
Knowing how it works under the hood
helps you to write better code.

29. λ
Thank you!
Any questions?

30. References
1. Our company - Appliscale.
2. Me - afronski.pl and my talks.
3. Functional Miners (facebook, twitter, github, email).
4. Hot-Code Reload (Learn You Some Erlang For Great Good)
5. Implementing Languages on the Erlang VM (R. Virding)
6. Virtually Instructional (L. Fridén)
7. Hack your own Erlang VM (R. Studnicki)
8. Core Erlang - Specification
9. Core Erlang - Documentation
10. A Peek Inside the Erlang Compiler (J. Hague)
11. Notes on Erlang Compiler (bhuztez)