Go backward to Scoping Rules Go up to Top Go forward to Example

Dynamic Scoping

• Contex of phrase determined by place(s) where its value is required.
• Example: macro definition and invocation.
  • LET I=E binds I to text E.
  • Invocation provides context for evaluation of E.
• Semantics of abstraction and application:

  E[[LAMBDA (I) E]] =
      lambda e. inFunction(
          lambda e'.lambda d. E[[E]](updateenv [[I]] d e'))
  E[[E₁ E₂]] =
      lambda e. let x = (E[[E₁]]e) in
          cases x of
              isFunction(f) -> (f e (E[[E₂]]e))
              [] otherwise -> inError()
          end

Statically scoped languages are difficult to understand.