A Lambda Calculus interpreter. Uses PEG.js, CoffeeScript, and Underscore.
- Built a Lambda Calculus interpreter in Haskell for a class (Design of Programming Languages with Professor Fred Martin and TA Nat Tuck at UMass Lowell Spring 2013)
- Thought of a way to emulate the pattern matching syntax of Haskell in CoffeeScript (see
- Learned how to use PEG.js to build a parser.
- Thought to generate an abstract syntax tree using simple object literals with a string
typeproperty (one of
- Had to write helper functions for the parser to achieve proper associativity for sequential apply statements and multi-argument lambdas.
- Ported Haskell interpreter to CoffeeScript (using Underscore when needed)
- Started by mixing pure functional (immutable AST nodes) and imperative (mutable AST nodes) styles
- Using mutable AST nodes led to an error where multiple references to the same node appeared multiple times in the tree (from the substitution step), leading to a stack overflow error when reducing due to circular reference (e.g. applying a node to itself).
- For safety, chose to go with pure functional style by always creating new AST nodes for all reduction steps
- Ideas for future work:
- Use a procedural style that mutates AST nodes during reduction steps.
- Instrument the code to count how many new AST objects are created.
- Visualize a table with the following columns:
- input - a lambda calculus expression (from unit tests)
new AST objects created in functional style
new AST objects created in procedural style