This a single-step interpreter for a subset of the Haskell language including integers, booleans, lists, tuples and recursive definitions. The principal focus is on simplicity since this is intended for teaching fundamentals of functional programming.
This project started as a re-implementation of the Lambda Lessons by Jan Paul Posma and Steve Krouse in Elm and extended with more features, e.g.:
- strings and characters;
- full pattern matching and boolean guards;
- case expressions;
- let and where bindings;
- algebraic data type definitions;
- lazy evaluation;
- definitions for commonly used functions from the Haskell Prelude.
This interpreter and associated lazy abstract machine are described in the paper Haskelite: A Tracing Interpreter Based on a Pattern-Matching Calculus (accepted for publication in the proceedings of the Haskell 2024 Symposium). A preprint version is available here.
The CodeView custom element is based on the code published by Bill St. Clair.
Please check the supported subset of the Haskell language here.
You can try the interpreter locally by opening the file
site/index.html using a web browser; several examples are also
available from this page. All the required HTML, CSS and JavaScript
files are bundled; no external files are downloaded and no internet
connection is needed.
The Elm source is in the src directory; some aditional open-source
JavaScript libraries are included in site/js.
To build the interpreter just run make from the main directory; this
will invoke elm make to download the Elm packages listed in
elm.json and compile all sources to a minimized haskelite-min.js
JS file. The following tools need to be installed:
- the Elm compiler;
- the uglyfy-js JavaScript minimizer (part of the NodeJS tools);
- a make tool (e.g. GNU make).
This software was developed in Ubuntu Linux with Firefox and tested with Chrome, but should work in other OSes and browsers provided they support reasonably recent CSS and JavaScript.
Pedro Vasconcelos, 2024.