Forth

Forth language! Implemented as a Racket #lang.

Install

From the package server:

> raco pkg install forth

From source:

> git clone https://github.com/bennn/forth
> raco pkg install ./forth

Usage

All files starting with #lang forth are interpreted as a sequence of Forth commands.

#lang forth

push 2      ;; add `2` to the stack
push 2
+           ;; add the top two numbers on the stack
dup         ;; duplicate head of stack
2           ;; short for `push 2`
swap        ;; swap order of top 2 stack arguments
-

: incr 1 +  ;; define a new command `incr`
incr
incr
+

To open an interactive session, run raco forth.

#lang Details

Running raco pkg install forth installs forth as a Racket package. Since the package contains a directory named lang/ that contains a file reader.rkt, the new package can be used as a #lang. Racket uses to reader defined in reader.rkt to process programs that begin with #lang forth. (Official docs here)

All reader.rkt modules need to provide the functions read and read-syntax. These functions must produce a Racket module (docs here).

In this project, read just calls read-syntax, which reads all lines from the file and interprets them as forth commands. The interpreting happens during compilation and produces a stack. After evaluating all commands in the module, our read-syntax function returns a module; inside the module, we save the stack to a variable. Doing so makes the stack available inside the Dr. Racket interactions panel.

One more thing: this package's info.rkt file defines the raco forth command. Docs here.)