Architectural changes to lambda evaluation and parsing to allow
for correct expression evaluation. Contains several failing AI-generated
tests and we're still failing tests for erroring incomplete definitions
Includes better error handling, additional tests, parsing and lexing
fixes to match the desired behavior defined by the new tests, and a very
basic REPL implementation.
Implemented evaluation of tree calculus terms alongside referentially
transparent variable identifiers. Implemented evaluation of defined
functions into tree calculus.
