Makefile

Introduction
The way to structure projects in Erlang is a mystery to me. In C++, it's simple because everything names itself in the projects:

/project
    include/
        project /
    src/
    test/
    resources/
    views/

Then in the root directory I normally place my qmake or premake4 files. This seems like second nature. After building we'd also end up with some other directories to hold binaries, libraries, and object files.

In Erlang we have the notion of macro/definition files (hrl's); we also have source code (erl's). The compiled output for Erlang is a beam file. How does everything normally get structured? To better answer this question I thought I'd examine the Erlang makefile.

Getting It

I grabbed a version from git:

> git clone https://github.com/extend/erlang.mk.git

This gives you erlang.mk. Have this handy to copy into your experimental directory.

Trying it Out

Follow the steps below to make a small test:

> mkdir experiment
> cd experiment
> cp erlang.mk ./ # Or wherever erlang.mk exists.
> vim Makefile # Or your editor of choice.

Inside of Makefile, just add:

include erlang.mk

And save. Back in the terminal try this:

> make

This won't work because we don't have any sources set up! It will complain with:

find: `src': No such file or directory
find: `src': No such file or directory
find: `src': No such file or directory
find: `src': No such file or directory
 APP    experiment.app.src
cat: src/experiment.app.src: No such file or directory

This is because we need to make a directory called src and put some Erlang sources inside of it:

> mkdir src
> cd src
> vim test1.erl

Put a test program inside of test1.erl, could be something simple like:

-module(test1).
-export([blah/0]).

blah() -> "Hello".

After saving, step down a directory and try to make again:

> cd ..
> make

This time it will create a directory called "ebin"; this is where all of the beam files end up. Some additional notes on structuring Erlang programs can be found here:

http://www.erlang.org/doc/design_principles/applications.html#7.4

The hrl files can go into an include directory.

Dependencies

We have our source code but we need to use other people's libraries/projects in our own. The Erlang Makefile is like a dream come true for this purpose: it can automatically pull down your required dependencies directly from git. I suspect it can do more than just that but for now we'll end with that.

In the line before include erlang.mk:

DEPS = eredis
dep_eredis = https://github.com/wooga/eredis.git
include erlang.mk

Now try building. Pretty impressive isn't it? The format here is to list your dependencies after DEPS, then for each entry you add a dep_ENTRY = followed by the location of the target library. The Makefile then automates building everything for you. I can't emphasize how cool this is, although most Erlang developers probably already know it.