Alee Forth

Alee Forth is a concise Forth implementation written in modern C++ that aims for portability, minimal memory footprint, and execution efficiency.

Cross-platform compatibility

Alee Forth relies on the C++20 standard. It does not rely on any operating system. As a result, portability extends down to microcontroller targets with < 16kB flash and < 1 kB of RAM. See the msp430 folder for an example of such a port.

System-specific functionality is achieved through a sys Forth word. This word calls a user-supplied C++ function that implements whatever functionality is needed.

Forth compatibility

Alee Forth uses the Forth 2012 test suite to ensure standards compliance. The entire "core" word-set is implemented as well as most of the "core extension" word-set. The compiled program contains a minimal set of fundamental words with libraries in the forth directory supplying these larger word-sets. The "core" word-set can be compiled into the program by building the standalone target.

Missing core extension words:

PARSE PARSE-NAME REFILL RESTORE-INPUT S\" SAVE-INPUT SOURCE-ID

Building

Alee requires make and a compiler that supports C++20. Simply running make will produce the libalee.a library and a REPL binary named alee. The core word-sets can be passed into alee via the command line: ./alee forth/core.fth forth/core-ext.fth.

Other available build targets:

• small: Optimize for minimal binary size.
• fast: Optimize for maximum performance on the host system.
• standalone: Builds the core dictionary (core.fth) into the binary.
• msp430-prep and msp430: Builds a binary for the MSP430G2553 microcontroller. See the msp430 folder for more information.

If building for a new platform, review these files: Makefile, libalee/types.hpp, and libalee/state.hpp. It is possible to modify the implementation to use 32-bit words, but this will require re-writing the core word-sets.