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CSE-321 Programming Languages Evaluation Contexts

CSE-321 Programming Languages Evaluation Contexts. 박성우. POSTECH April 16, 2007. Simply Typed  -Calculus. 18 Reduction Rules. Simpler?. Outline. Evaluation contexts Abstract machine C. Reduction Rules. Derivation Trees. Reducing an Expression e.

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CSE-321 Programming Languages Evaluation Contexts

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  1. CSE-321 Programming LanguagesEvaluation Contexts 박성우 POSTECH April 16, 2007

  2. Simply Typed -Calculus

  3. 18 Reduction Rules

  4. Simpler?

  5. Outline • Evaluation contexts • Abstract machine C

  6. Reduction Rules

  7. Derivation Trees

  8. Reducing an Expression e • Locate an appropriate subexpression (redex) of e • Apply a corresponding reduction rule

  9. Locate and Apply

  10. Decompose and Apply = +

  11. Decompose and Apply Expression = Redex + Context remaining intact

  12. Evaluation Contexts (CBV) • An expression with a hole ¤ in it • The hole ¤ indicates the position of a subexpression to be reduced in the next step,i.e., the redex for the next step. • Example:

  13. Reduction Strategy • Determined by the definition of evaluation contexts call-by-value call-by-name

  14. Reduction Rule

  15. Example

  16. Still Cryptic?

  17. Outline • Evaluation contexts V • Abstract machine C

  18. This Rule is a Sagi.

  19. Example • Implicit analysis • Explicit analysis

  20. Abstract Machine C • Explicit decomposition of a given expression • Uses a stack of frames instead of evaluation contexts. • Each frame corresponds to a specific step in the decomposition.

  21. Example

  22. State of the Machine

  23. Example

  24. Outline • Evaluation contexts V • Abstract machine C V • Something important!

  25. Midterm • Three hours, closed book • 20% toward your final grade • Next Wednesday, 8pm - 11pm, in the classroom April 2007 Su Mo Tu We Th Fr Sa 16 17 18 19 20 21 22 23 24 25 26 27 28

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