Adding an extension module to ABC without modifying ABC

This repository contains an example on how to add a module to ABC without modifying ABC itself. This has several advantages:

• You can easily update to newer version of ABC.
• You can put this in a separate source control repository.
• You can easily combine multiple such projects without any additional modification to ABC.

This examples add a command @hello, that prints out a greeting and its arguments.

Instructions

1. Clone the ABC repository

git clone https://github.com/berkeley-abc/abc.git

2. Extract this repository under src/

cd abc/src
git clone https://github.com/berkeley-abc/ext-hello-abc

3. Build ABC

make

4. Run the new command

$ ./abc
UC Berkeley, ABC 1.01 (compiled Mar 11 2018 00:55:29)
abc 01> @hello 1 2 3
Hello world!
  argv[0]: @hello
  argv[1]: 1
  argv[2]: 2
  argv[3]: 3
abc 01>

Some Details

.gitignore

ABC's .gitignore file also ignores src/ext*, to prevent accidentally adding your extensions to ABC.

Makefile

The ABC Makefile is based on the classic paper Recursive Make Considered Harmful.

The Makefile has a variable named MODULES that contains a list of subdirectories where it looks for files named module.make. The module.make file should add the module's source files to the variable SRC.

The MODULES varialbe also contains a line

$(wildcard src/ext*) 

which instructs it to look for module.make files under any directory under src/ whose name starts with ext.

Adding Commands to ABC

To run your code as part of ABC, you need to register commands. To do that, we provide an way of registering functions to be called on ABC startup and termination. This is demonstrated in init.cpp.

1. Write an init() and destroy() functions.

2. Create a global initializer object:

Abc_FrameInitializer_t frame_initializer = { init, destroy };

3. Register the initializer object:

Abc_FrameAddInitializer(&frame_initializer);

This is best done before main() is called. The simplest way to do that is in C++, by using a constructor of a global obejct, as constructors of global objects are called before main().