Expect semicolon after 'ret' statement.
Test parsing function declarations.
Use 'lam' for lambdas; parse and evaluate them.
Test lambdas.
Catch and report parse errors in unit tests.
Rename 'FunExpression' to 'FunValue'.
Add stream insertion operator for 'Environment'.
Kill dead character.
Use correct lexical environment for lambdas.
Test currying and interaction with 'whenever' statement.