CSE321 Programming Languages Evaluation Contexts and Abstract Machine C

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CSE-321 Programming LanguagesEvaluation Contexts
and Abstract Machine C
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• POSTECH
• April 12, 2006

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Simply Typed ?-Calculus
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18 Reduction Rules
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Simpler?
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Outline

• Evaluation contexts
• Abstract machine C

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Reduction Rules
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Derivation Trees
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Reducing an expression e

• Locate an appropriate subexpression
• Apply a corresponding reduction rule

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Locate and Apply
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Decompose and Apply


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Decompose and Apply
Expression

Subexpression to be reduced

Context to remain intact
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Evaluation Contexts (CBV)

• An expression with a hole in it
• The hole indicates the position of a
  subexpression to be reduced.

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Reduction Strategy

• Determined by the definition of evaluation
  contexts

call-by-value
call-by-name
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(No Transcript)
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Reduction Rule
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Still Cryptic?
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Outline

• Evaluation contexts V
• Abstract machine C

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This Rule is a Sagi.
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Example
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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.

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State of the Machine
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Example
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(No Transcript)
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Outline

• Evaluation contexts V
• Abstract machine C V
• Something VERY important!

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Midterm

• One and half hours
• Midterm 10 15, final 20 25
• April 2006
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