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Environments

Mathematical value that models context.

1. Environment establishes context for syntactic phrase

   Resolution of ambiguities concerning meaning of identifiers.

2. As many environment values as distinct program contexts.

   Multiple environments are maintained during program evaluation.

3. Environment is a static object.

   Phrases uses the same environment each time it is evaluated.

• Simple model: store = environment
  • Only one environment.
  • Used in previous program examples.
• Complex model: store + environments.
  • One store.
  • Multiple environments.