Alee Forth

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

Cross-platform compatibility

Alee relies on the C++17 standard. Alee does not rely on operating-system-specific functions, making portability easy.

The goal of portability extends down to microcontroller targets with kilobytes of memory. See the msp430 target for an example of a port.

System-specific functionality is obtained through a sys Forth word. This word calls a user-supplied C++ function that implements the necessary (or any additional) functionality.

Forth compatibility

Alee implements a large majority of the "core" and "core extension" glossaries. Implementation is tracked in compat.txt, with missing words listed below. Fundamental words are built into Alee (written in C++); the rest of the implementation is in core.fth.

This means Alee should be executed as alee core.fth to include these words. Alternatively, the standalone target packages the core.fth dictionary into the program.

Missing core features:

• Pictured numeric output conversion <# #>
• Words for unsigned integers: U. U< UM* UM/MOD
• >NUMBER
• FIND

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 C++17-compatible compiler.

To compile, simply run the make command. This will produce a library, libalee.a, as well as a REPL binary named alee.
A small target exists that optimizes the build for size.
A fast target exists that optimizes for maximum performance on the host system. The standalone target will produce a alee-standalone binary that contains and pre-loads the core dictionary. The msp430 target builds Alee for the MSP430G2553 microcontroller. Like standalone, the core dictionary is built into the binary.

Configurable constants and types are defined either in the Makefile or in types.hpp.