Demo of a WAM Prolog implementation in Python

This is a simplified Warren Abstract Machine (WAM) implementation for Prolog, that showcases the main instructions, compiling, register allocation and machine functions.

Code organization

  • Data objects representing terms, programs, and machine entities.
  • Compiling of a list of rules into a list of instructions.
  • Interpreter that execute the instruction listing for a given query.
  • Sample application of interpreter, with a grammar that can parse itself. Try it out with python -m grammar and compare with the text in the file!


  1. About Prolog: a hurried primer if you don’t know what it is about.
  2. Resolution strategy: how a query is actually solved in Prolog.
  3. Warren Abstract Machine: details about the implementation attempted here.
  4. Indexing: indexing implementation to fast-track some call patterns.
  5. Parsing: explaining basic structures for parsing
  6. : documentation for the sample application of grammar parsing.
  7. Stuff left out: what this implementation has simplified from the WAM, and references.


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