CSE321 Programming Languages Evaluation Contexts and Abstract Machine

CSE-321 Programming Languages Evaluation Contexts and Abstract Machine C 박성우 POSTECH April 12, 2006

Simply Typed -Calculus 2

18 Reduction Rules 3

Simpler? 4

Outline • Evaluation contexts • Abstract machine C 5

Reduction Rules 6

Derivation Trees 7

Reducing an expression e • Locate an appropriate subexpression • Apply a corresponding reduction rule 8

Locate and Apply 9

Decompose and Apply = + 10

Decompose and Apply Expression = Subexpression to be reduced + Context to remain intact 11

Evaluation Contexts (CBV) • An expression with a hole ¤ in it • The hole ¤ indicates the position of a subexpression to be reduced. 12

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

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Reduction Rule 15

Still Cryptic? 16

Outline • Evaluation contexts V • Abstract machine C 17

This Rule is a Sagi. 18

Example 19

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. 20

State of the Machine 21

Example 22

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

Midterm • One and half hours • Midterm 10% $ 15%, final 20% $ 25+% Su 9 16 23 30 Mo 10 17 24 April Tu We 11 12 18 19 25 26 2006 Th Fr 13 14 20 21 27 28 Sa 15 22 29 25