cl-forth: Forth 2012 Standard in CL

The release of CL-Forth gives Lisp developers a native way to run Forth 2012 code inside their Lisp environment, eliminating the need for external Forth systems or custom bindings. This changes the workflow for engineers who want to prototype or script using Forth’s stack-based syntax while staying within a familiar Lisp toolchain. It also provides a reference implementation for those studying the Forth 2012 Standard. The change is primarily about accessibility rather than a new feature set.

Adopting CL-Forth requires installing ASDF, CFFI, and trivial-gray-streams via QuickLisp, loading the ASDF system, and optionally building a standalone executable with the provided save-application form. The MIT license imposes no legal restrictions, and the dependencies are already common in many Lisp projects, so the cost is mainly the initial setup time. No additional runtime fees or special hardware are needed. Engineers can start using it immediately after the quickload steps.

CL-Forth does not implement the Block word set, the Extended-Character word set, or the KEY word from the Core set. It also omits many Facility extension words such as AT-XY, KEY?, PAGE, and the various key-mask and arrow-key symbols (K-ALT-MASK, K-UP, etc.). Programs that depend on any of these missing words will not run correctly without further implementation or workarounds. This limits its suitability for applications that rely heavily on hardware interaction or advanced terminal features.

An experimental optimizer is included; when turned on with OPTIMIZER ON it reduces object code generation and speeds up the Forth test suite on SBCL (approximately 33% faster and 25% less code). The optimizer is off by default, so engineers must explicitly enable it to gain the performance benefit. The optimizer works by eliminating unnecessary data-stack use and redundant validity checks. Its presence offers a tangible upside for performance-sensitive embeddings, though it remains optional.