CS3723: Concepts in Programming Languages - Skills and Concepts Covered, Study notes of Programming Languages

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Review

Concepts in Programming

Languages

What we have learned

 Skills  Language syntax (context-free grammar, parse tree, and AST)  Lambda calculus (apply beta reduction)  Functional programming (recursion in Scheme and ML)  Type inference (from Scheme to ML or C)  Tail recursion, loops, and continuation passing (methods of programming)  Object-oriented programming (from ML datatype/abstype to C++ classes)  Knowledge (concepts)  Language semantics (expressing power, interpretation vs. compilation, higher-order functions, functions as first-class objects)  Types, type checking and type inference; Polymorphism  Memory management (blocks, functions, classes and inheritance)  Continuation and exceptions  Abstractions, object-oriented abstractions,  C++ and Java language design and implementations  Advanced topics  What if we modify a language by adding …

Skills

Lambda Calculus

 Higher order functions to the extreme

 Use functions to express everything

 Key: understand function abstractions and

function applications

 Exercise: apply beta reductions

 λ x. (λ y. y x) (λ z. x z)

 (λ x. (λ y. y x) (λ z. x z) ) (λ y. y z)

 (λ y. (λ x. λ y. x (x y)) (λ g. g y)) 5

Skills---

Blocks and Memory Management

 Key: understand the algorithm (get pass the syntax barrier)  Function definitions can be nested inside one another, but a function block is not entered untilled the function is invoked by a caller  Exercise: list the order of events for the following code; then draw the runtime stack snapshot. 1: let 2: fun mk_x(x) = 3: let fun add1(y) = x + y 4: in 5: let val x = 7 in add1(5) end 6: end 7: fun apply(f,x) = f(x) 8: in 9: apply(mk_x,10)- 10:end;

Concepts:

Languages and Functions

 Why high-level programming languages?  Productivity, portability, maintenability, machine efficiency  What can programming languages express?  Data and algorithms  Partial recursive functions  Programming paradigms  Can you define what they are and give examples?  Functional, imperative, object-oriented  What is a high-order function? What does “functions are first- class objects” mean?  In what ways can prog. languages be implemented? Give examples? What is the trade-off? What are the implementation phases  Compilation vs. interpretation  Lexical analysis, Syntax analysis, semantic analysis, interpretation/code generation+optimziation

Concepts --- Types

 What is a type? What is it used for?

 Types are classification of values  Different types of values have different layout/interpretation

 Type declaration and equivalence

 Name vs. structure type equivalence

 What is a type system

 How to determine types of variables and expressions?  Compile-time vs. runtime type checking  Type checking vs. type inference  Compile-time vs. runtime type checking  Type safety of languages

 Polymorphism

 Parametric, ad-hoc and subtype polymorphism

Concepts--

Implementing Functions

 How many ways can parameter values be passed?  Pass by value vs. pass by reference  What is a function closure? What is it used for?  The value of a function <code, env>  Used to setup environment for function calls  Why is implementing higher-order functions hard?  When a function returns other functions, the activation records needs to be saved  Activation record in the heap  OO languages  What is tail recursion? Why is it equivalent to loops?  Tail recursion: do not need to return  What is a continuation? What is continuation passing  Continuation: the rest of computation after function exit

Concepts: Exceptions

 Why are exceptions considered dynamic jumps?  Static jumps: goto, loop, conditionals, …  Exception:  Jump out of one or many levels of nested blocks  Until reaching some program point to continue  Pass information to the continuation point  What is required from a language to support expections?  Type (exception) declaration  Raise an exception  Handle an exception  Are exceptions part of the type system?  Raising of exceptions not part of type system  Handling of exceptions need to agree with type system

Object-oriented Abstractions

 OO abstractions are types

 Have constructors and can be used to build objects  Grouping of relevant data and functions  Access control: private, protected, public, friend, package

 Encapsulation

 Separate interface from implementation details

 Subtype polymorphism

 Values of subtypes can be used to substitute base type values

 Dynamically-bound functions

 Function pointers stored inside class objects  Virtual function are looked up at runtime

 Implementation inheritance

 Derived classes can redefine virtual functions of base classes

Object-oriented languages

 C++/Java classes vs. ML datatype + scoping

(nested functions)

 ML can simulate most features of C++/Java except  Inheritance and extensibility  Java/C++ encapsulation  ML function closure  Java/C++ namespaces ML structures/signatures  Java/C++ virtual methodsfunction pointers as values  Java/C++ subtyping  union types and pattern matching

 Implementation of classes C++ vs. Java

 Layout of class objects and Java interfaces  Managing class member functions  Design philosophies of the two languages