09 Type-based Analysis

09 Type-based Analysis - Section Outline Type and...

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Unformatted text preview: Section Outline Type- and Constraint-Based Analysis Constraint-based Analysis Type-based Analysis ◮ Type Systems ◮ Type Inference ◮ Steensgaard’s Flow-Insensitive Pointer Analysis Relation to Datafow Analysis Ben Hardekopf () CS 290C Program Analysis Fall 2011 1 / 71 Section Outline Type- and Constraint-Based Analysis Constraint-based Analysis Type-based Analysis ◮ Type Systems ◮ Type Inference ◮ Steensgaard’s Flow-Insensitive Pointer Analysis Relation to Datafow Analysis Ben Hardekopf () CS 290C Program Analysis Fall 2011 2 / 71 What Is A Type? Definition (Type) A type is a set of related values, or equivalently, a logical predicate. Types approximate values. An expression of type τ must have a value that belongs to the set of values described by τ . Ben Hardekopf () CS 290C Program Analysis Fall 2011 3 / 71 What Is A Type? Definition (Type) A type is a set of related values, or equivalently, a logical predicate. Types approximate values. An expression of type τ must have a value that belongs to the set of values described by τ . Example The statement “ exp : int ” states that expression exp evaluates to an integer. It is equivalent to the predicate int ( exp ) = true . Ben Hardekopf () CS 290C Program Analysis Fall 2011 3 / 71 What Is A Type? Definition (Type) A type is a set of related values, or equivalently, a logical predicate. Types approximate values. An expression of type τ must have a value that belongs to the set of values described by τ . Example The statement “ exp : int ” states that expression exp evaluates to an integer. It is equivalent to the predicate int ( exp ) = true . Example (Common Types) Type Description Example int integers 42 bool boolean values true int [ ] array of integers [1, 1, 2, 3] int → bool functions from int to bool fun ( x : int ) { return x ≤ } Ben Hardekopf () CS 290C Program Analysis Fall 2011 3 / 71 What Are Types Good For? Types prevent certain kinds of semantically nonsensical computations, i.e., computations that are not defined in the semantics of a language. Example (Ill-typed Program) def foo = fun (x) { y := x+1 ; return y } z := 1 + foo Ben Hardekopf () CS 290C Program Analysis Fall 2011 4 / 71 What Are Types Good For? Types prevent certain kinds of semantically nonsensical computations, i.e., computations that are not defined in the semantics of a language. Example (Ill-typed Program) def foo = fun (x) { y := x+1 ; return y } z := 1 + foo But not all kinds of errors. A program can still compute something of the right type , but the wrong value . Example (Well-typed, but Incorrect Program) def AbsVal = fun (x) { if (x < 0) then { y := x } else { y := 0-x } ; return y } z := AbsVal(10) Ben Hardekopf () CS 290C Program Analysis Fall 2011 4 / 71 Terminology There is a lot of confusion surrounding typing and its terminology. People often use the terms incorrectly or inconsistently, which can make the debates about typing very frustrating. Here we’ll lay out a number ofdebates about typing very frustrating....
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This note was uploaded on 12/27/2011 for the course CMPSC 290a taught by Professor Vandam during the Fall '09 term at UCSB.

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09 Type-based Analysis - Section Outline Type and...

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