Implement behavioral properties for functions including:
- Property annotations: is pure, is total, is idempotent, is deterministic, is commutative
- Where clause constraints: where F is pure
- Result refinements: where result >= 0 (parsing only, not enforced)
Key changes:
- AST: BehavioralProperty enum, WhereClause enum, updated FunctionDecl
- Lexer: Added keywords (is, pure, total, idempotent, deterministic, commutative, where, assume)
- Parser: parse_behavioral_properties(), parse_where_clauses(), parse_single_property()
- Types: PropertySet for tracking function properties, updated Function type
- Typechecker: Verify pure functions don't have effects, validate where clause type params
Properties are informational/guarantees rather than type constraints - a pure
function can be used anywhere a function is expected. Property requirements
are meant to be enforced via where clauses (future work: call-site checking).
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
