Let's Build Objects in GForth

2016-01-02 04:56:00 UTC

Although FORTH is considered by many to be a procedural language, its flexibility has allowed it to adapt other programming styles as well. If you are running GForth (HINT: sudo apt-get install gforth ), you already have access to a great object oriented programming (OOP) library called oop.fs .

The documentation is well written, but might be a little bit wordy if you just want to play around.

Below is an example of OOP in GForth that will cover 80% of the use cases:

Instance CRUD

Instance level variable CRUD

Method definitions

Method calls

Inheritance

\ include oof.fs for GFORTH OOP. There's also mini-oof.fs, which is \ only 12 lines long and gives you (most of) the same functionality \ in a smaller package include oof.fs \ Let's define a class called "square". It inherits from the object \ class, which is the mother of all classes in oof.fs. \ Syntax: <parent> class <child> object class square \ Give it an instance method called "area" method area \ Give instances of square 2 cells of memory. \ On my system, that means 128 bytes. 1 cells var length 1 cells var width \ Now that class "square" is defined, we can implement it. how: \ Constructor expects 2 integers on the stack when called: width \ and length. : init ( n-width n-length -- self ) \ Take the first item on the stack (length) and store that into \ the instance variable "length". length ! \ Same thing for width width ! ; : area ( self -- n-area ) \ Grab length and push onto stack length @ \ Grab width and push onto stack width @ \ Multiply length by width * ; class; \ Create a new instance of square called "my-square" 20 30 square : my-square \ Call the method "my-square" on square instance "my-square"... \ ... Print the return value to screen. my-square area . cr \ Destroy the square object (for example purposes) my-square dispose \ gracefully exit. bye

I hope that helps. If you have any questions, you can always ask the friendly folks at /r/forth.