Alee Forth

Alee Forth is a concise Forth implementation written in modern C++ that aims for portability, minimal program size, 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 < 1 kB of memory. See the msp430 folder for an example of such a port.

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

Forth compatibility

Alee implements the entire "core" and majority of the "core extension" word-sets. Implementation is tracked in compat.txt with missing words listed below. Fundamental words are hard-coded into Alee while the rest of the implementation is found in forth/core.fth and forth/core-ext.fth. Running Alee without these implementation files will leave you with a very minimal word-set. These files may be compiled into the Alee binary by building the standalone target.

Missing core extensions:

.R HOLDS PAD PARSE PARSE-NAME REFILL RESTORE-INPUT S\" SAVE-INPUT SOURCE-ID U.R U> UNUSED WITHIN [COMPILE]

Alee aims for compliance with common Forth standards like Forth 2012 and ANS Forth. Compliance is tested using a Forth 2012 test suite. Supported test files are in the test directory with tests for unimplemented words commented out.

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. You will likely want to pass in the core implementation files by calling ./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.