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Program Testing and Analysis:

Operational Semantics

Dr. Michael Pradel

Software Lab, TU Darmstadt

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Warm-up Quiz

var e = eval;

(function f() {var x = 5;e("x=7")console.log(x);

})();

What does the following code print?

Options: 5, 7, or something else

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Warm-up Quiz

var e = eval;

(function f() {var x = 5;e("x=7")console.log(x);

})();

Correct answer: 5

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Warm-up Quiz

var e = eval;

(function f() {var x = 5;e("x=7")console.log(x);

})();

Correct answer: 5

eval() evaluatesJavaScript codegiven as a string

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Warm-up Quiz

var e = eval;

(function f() {var x = 5;e("x=7")console.log(x);

})();

Correct answer: 5

Store function into variable(functions are first-classobjects)

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Warm-up Quiz

var e = eval;

(function f() {var x = 5;e("x=7")console.log(x);

})();

Correct answer: 5

Define a function andcall it immediately

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Warm-up Quiz

var e = eval;

(function f() {var x = 5;e("x=7")console.log(x);

})();

Correct answer: 5

Indirect eval():Works in globalscope rather thanlocal scope

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Follow Up on Last Week

(Hand-written notes)

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Big Picture

Last lecture:� Syntax of languages

� Representations of programs

This lecture:� Assign meaning (= semantics) to programs

� Focus: Operational semantics of imperativelanguages

� Formal foundation for specifying languages andfor describing dynamic analyses

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Plan for Today

� Motivation & preliminaries

� Abstract syntax of SIMP

� An abstract machine for SIMP

� Structural operation semantics forSIMP� Small-step semantics

� Big-step semantics

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Plan for Today

� Motivation & preliminaries

� Abstract syntax of SIMP

� An abstract machine for SIMP

� Structural operation semantics forSIMP� Small-step semantics

� Big-step semantics

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Plan for Today

� Motivation & preliminaries

� Abstract syntax of SIMP

� An abstract machine for SIMP

� Structural operation semantics forSIMP� Small-step semantics

� Big-step semantics

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