About this notebook

What is covered

Besides the core language, the lessons cover logic programming in depth: the syntax and execution model, resolution and unification (resolvents, substitutions, most general unifiers), Peano arithmetic and data types programmed from scratch, full relationality, tail recursion and immutability, searching the solution space, cut, term inspection, operators and DSLs, dynamic theories and every metainterpreter variant (resolution, vanilla, built-ins and control, reverse order, tracing with a size bound), and a hands-on constraint programming lesson. Programs whose names clash with built-ins of other systems may differ slightly from other environments; the lessons say so where it matters.

About the author

PrologEZ is created by Luca Bonaldo. Find more of his work, projects and writing on his website, lucabonaldo.dev, and on GitHub. The source code, issues and contributions for PrologEZ live in the GitHub repository.

What runs your code

Every cell executes on SWI-Prolog 9, compiled to WebAssembly and running in a background thread of your browser. Nothing is sent to a server. The first run takes a moment while the engine loads (about 4 MB, cached afterwards).

How cells work

• A program cell adds clauses to a knowledge base. Press Load to check it for errors.
• A query cell runs against all program cells above it in the lesson. Use Ctrl/⌘ + Enter to run, or Enter in a query box.
• Every run starts from a clean slate: the program is loaded fresh, the query runs once, and anything it asserted is forgotten afterwards.
• Up to ten solutions are shown per query. Ask for more specific ones, or use findall/3.
• Runaway queries (infinite loops, endless recursion) are stopped automatically, or press Stop.
• Your edits, exercise solutions and progress are stored in this browser only (localStorage). Use Reset lesson to start a lesson over.

Differences from the interactive toplevel

• There is no keyboard input: read/1 just hits end-of-file.
• Answers are printed all at once instead of one by one with ;.
• halt/0 stops the engine; it restarts on the next run.
• Output of write, format and friends appears above the answers.

Going further

When you're comfortable, install SWI-Prolog locally and read the manual. Everything in this notebook runs there unchanged.