Liquid-Oxygen

A tree-walk interpreter for the Lox language, based on the first half of the book, Crafting Interpreters by Robert Nystorm.

Cabal

REPL

cabal run liquid-oxygen

Interpret script

cabal run liquid-oxygen <script>

Resources

• Crafting Interpreters by Robert Nystorm

Notes:

Will be optimized further.

Linked Lists

• [Char] (String) is just a linked list of characters, which is inefficient.
• Alternatives like Text (from text) or ByteString (from bytestring) are much faster and more memory-efficient.
• Similarly, for other linked list operations, other structures like Vector or Seq can offer better performance depending on use case.

Resolving

• The original implementation uses a locals map to track only local variable resolutions.
• My implementation uses distances, which uniformly tracks local and global by their scope depth.

Initialize vs Assign

• Only modifyIORef (lazy) works for initialize due to Functions, because closures depend on lazily init envs and may involve cyclic refs (mdo / fixIO).
• atomicModifyIORef (strict) seems to work safely for assignAt, since assignment happens after eval and does not involve cyclic structs.