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Lecture 2 Concepts of Programming Languages

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1 Lecture 2 Concepts of Programming Languages
Arne Kutzner Hanyang University / Seoul Korea

2 Concepts of Programming Languages
Topics Reasons for Studying Concepts of Programming Languages Programming Domains Language Evaluation Criteria Influences on Language Design Language Categories Language Design Trade-Offs Implementation Methods Programming Environments Concepts of Programming Languages

3 Reasons for Studying Concepts of Programming Languages
Improved background for choosing appropriate languages Reduction of the risk of wrong decisions Better use of languages that are already known Better understanding of significance of language implementations Concepts of Programming Languages

4 Concepts of Programming Languages
Programming Domains Business applications E.g. Middleware that implements some business process Java, COBOL (still popular here!) Web programming Languages: markup (e.g., HTML), scripting (e.g., PHP), general-purpose (e.g., Java) General purpose applications Examples: Photoshop, Autocad, Word …. Reliability and efficiency are important Systems programming / Operating System implementation Low level, code efficiency is very important C, Assembler Scientific applications E.g. Simulations; computational expensive tasks Fortran, (C, C++) Artificial intelligence Experimental work with languages like LISP (Scheme) and Prolog However, still on the level artificial stupidity Concepts of Programming Languages

5 Language Evaluation Criteria
Readability: Is this code easily readable? Writability: Do you like this coding? [>++++[>++>+++>+++>+<<<<-]>+>+>->>+[<]<-]>>.> >>.<-.< >>+.>++. Hello World in Brainfuck ( Reliability: unexpected crashes, blue screen of death Cost: $ $ $ $ $ … Concepts of Programming Languages

6 Evaluation Criteria: Readability / Writability
Overall readability/writability Are the constructs of the language self describing/intuitive/well human readable … Syntax considerations Special symbols and their meaning (e.g. creation of compound statements) Special words, meaningful keywords Data types and structures Adequate predefined data types and structures The presence of adequate facilities for defining new data structures Concepts of Programming Languages

7 Evaluation Criteria: Readability / Writability
Support for abstraction The ability to define and use complex structures or operations in ways that allow details to be ignored Expressivity A set of relatively convenient ways of specifying operations Strength and number of operators and predefined function Concepts of Programming Languages

8 Evaluation Criteria: Reliability
Static type checking vs. dynamic type checking Recognition of type errors during compile time / runtime Exception handling Intercept run-time errors and take corrective measures Concepts of Programming Languages

9 Evaluation Criteria: Cost
Training programmers to use the language Language implementation system: Availability of free compilers Reliability: poor reliability leads to high costs Maintenance costs Deployment costs Concepts of Programming Languages

10 Further Evaluation Criteria …
Portability The ease with which programs can be moved from one implementation to another Generality The applicability to a wide range of applications Well-definedness The completeness and precision of the language’s official definition Concepts of Programming Languages

11 Influences on Language Design
Computer Architecture Architecture as driving factor of language design. E.g. Von Neumann Architecture OpenCL/CUDA for computing on GPUs Programming Methodologies Abstract data types concept of object orientation Computational models / Mathematical models for computation Lambda Calculus, Predicate Logic Concepts of Programming Languages

12 Von Neumann Architecture
Concepts of Programming Languages

13 Programming Methodologies History / Mainstream developments
1950s and early 1960s: Simple applications; worry about machine efficiency Late 1960s: People efficiency became more important; readability, better control structures structured programming top-down design and step-wise refinement Late 1970s: Process-oriented to data-oriented data abstraction Middle 1980s: Object-oriented programming Data abstraction + Inheritance + Polymorphism Appearance of C++, Eiffel … Concepts of Programming Languages

14 Concepts of Programming Languages
Imperative Languages Inspired by von Neumann computers Data and programs stored in memory Memory is separate from CPU Instructions and data are piped from memory to CPU Characteristics of imperative languages Variables model memory cells Assignment statements used for assigning values to memory cells Iteration represents central concept Popular examples: C, Pascal Concepts of Programming Languages

15 Language Categories / Families
Imperative Comprises languages that support object-oriented programming Comprises scripting languages Examples: C, Java, Perl, JavaScript, Visual BASIC .NET, C++, C# Markup/programming hybrid Markup languages extended to support some programming Examples: HTML, XML, PHP, XSLT Functional Main means of making computations is by applying functions to given parameters Examples: LISP, Scheme, Haskell Logic Rule-based (rules are specified in no particular order) Example: Prolog Concepts of Programming Languages

16 Language Design Trade-Offs
Reliability vs. Cost of execution Example: Java demands all references to array elements be checked for proper indexing, which leads to increased execution costs Writability (flexibility) vs. Reliability Example: C pointers are powerful and very flexible but they are unreliable Concepts of Programming Languages

17 Implementation Characteristics of languages
Compilation Programs are translated directly into machine language Pure Interpretation Programs are interpreted by another program known as an interpreter Hybrid Implementations A compromise between compilers and pure interpreters Concepts of Programming Languages

18 Concepts of Programming Languages
Compilation Translate high-level program (source code) into machine code (executable file) Slow translation, fast execution Phases of compilation process: Lexical analysis: converts characters in the source program into lexical units Syntax analysis: transforms lexical units into parse trees which represent the syntactic structure of program Semantics analysis: generate intermediate code Optimization: automatically apply improvements Code generation: machine code is generated Concepts of Programming Languages

19 Additional Compilation Terminology
Linking: the process of collecting “objects files” for creating an executable file as output. Concepts of Programming Languages

20 Concepts of Programming Languages
Pure Interpretation Advantages No translation/compilation required Disadvantages Errors are recognized during runtime Slow execution speed (10 to 100 times slower than compiled programs) No static type-check, because of the absence of compilation Significant in the area of Web scripting languages (e.g. JavaScript, PHP) Concepts of Programming Languages

21 Hybrid Implementation Systems
A compromise between compilers and pure interpreters A program code is first translated to an intermediate code (called byte code) for later execution on a virtual machine Faster than pure interpretation More portable than compiled code Examples Java, C# Concepts of Programming Languages

22 Hybrid Implementations
Write Source Code Source Code program text in human readable form all 5 steps of compilation Compile Source Code Byte Code represents an intermediate code using a byte-code interpreter Execute Byte Code Concepts of Programming Languages

23 Just-in-Time Compilation
Optimization for hybrid implementations Instead of interpreting the byte-code the byte-code is first compiled into machine code and this machine code is executed direct on processor level Higher performance compared to interpretation JIT-compilation requires initially extra time. So it delays code execution / program start Nowadays standard with most hybrid implementations Concepts of Programming Languages

24 Concepts of Programming Languages
Preprocessors A preprocessor processes/changes source code before it is compiled Works like a macro mechanism and implements a text to text transformation C, C++ preprocessor expands #include, #define, and similar macros Not popular outside C and C++ Main disadvantage: Compiler error messages can become quite cryptic/strange Concepts of Programming Languages

25 Integrated Development Environments
Not part of the programming language itself; only supportive tools for convenient software development Popular examples: Microsoft Visual Studio tools: Supports MS-compiler for C#, Visual BASIC.NET, Jscript, J#, and C++ Eclipse Open programming environment that supports many programming languages NetBeans An integrated development environment for Java provided by Oracle Concepts of Programming Languages

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