High-level programming language

In computing, a high-level programming language is a programming language with strong abstraction from the details of the computer. In comparison to low-level programming languages, it may use natural language elements, be easier to use, or more portable across platforms. Such languages hide the details of CPU operations such as memory access models and management of scope.

A high level language isolates the execution semantics of a computer architecture from the specification of the program, making the process of developing a program simpler and more understandable with respect to a low-level language. The amount of abstraction provided defines how 'high level' a programming language is. [ [http://www.ittc.ku.edu/hybridthreads/glossary/index.php HThreads - RD Glossary ] ]

Historical Note

The first high-level programming language was the "Plankalkül", created by Konrad Zuse.

Features

The term "high-level language" does not imply that the language is always superior to low-level programming languages - in fact, in terms of the depth of knowledge of how computers work required to productively program in a given language, the inverse may be true. Rather, "high-level language" refers to the higher level of abstraction from machine language. Rather than dealing with registers, memory addresses and call stacks, high-level languages deal with usability, threads, locks, objects, variables, arrays and complex arithmetic or boolean expressions. In addition, they have no opcodes that can directly compile the language into machine code, unlike low-level assembly language. Other features such as string handling routines, object-oriented language features and file input/output may also be present.

Abstraction penalty

Stereotypically, high-level languages make complex programming simpler, while low-level languages tend to produce more efficient code. "Abstraction penalty" is the barrier preventing applying high level programming techniques in situations where computational resources are limited. High level programming features like more generic data structures, run-time interpretation and intermediate code files often result in slower execution speed, higher memory consumption and larger binary size [cite paper
author = Surana P
title = Meta-Compilation of Language Abstractions.
date = 2006
url = ftp://lispnyc.org/meeting-assets/2007-02-13_pinku/SuranaThesis.pdf
format = PDF
accessdate = 2008-03-17 ] [cite web
last = Kuketayev
title = The Data Abstraction Penalty (DAP) Benchmark for Small Objects in Java.
url= http://www.adtmag.com/joop/article.aspx?id=4597
accessdate = 2008-03-17 ] [ Citation
last = Chatzigeorgiou
last2 = Stephanides
editor-last = Blieberger
editor2-last = Strohmeier
contribution = Evaluating Performance and Power Of Object-Oriented Vs. Procedural Programming Languages
title = Proceedings - 7th International Conference on Reliable Software Technologies - Ada-Europe'2002
year = 2002
pages = 367
publisher = Springer
url = http://books.google.com/books?id=QMalP1P2kAMC&dq=%22abstraction+penalty%22&lr=&source=gbs_summary_s&cad=0 ] . For this reason, code which needs to run particularly quickly and efficiently may be written in a lower-level language, even if a higher-level language would make the coding easier.

However, with the growing complexity of modern microprocessor architectures, well-designed compilers for high-level languages frequently produce code comparable in efficiency to what most low-level programmers can produce by handFact|date=March 2008, and the higher abstraction may allow for more powerful techniques providing better overall results than their low-level counterparts in particular settings. [citation
author = Manuel Carro, José F. Morales, Henk L. Muller, G. Puebla, M. Hermenegildo
title = Proceedings of the 2006 international conference on Compilers, architecture and synthesis for embedded systems
contribution = High-level languages for small devices: a case study
url = http://www.clip.dia.fi.upm.es/papers/carro06:stream_interpreter_cases.pdf
format = PDF
date = 2006
publisher = ACM]

Relative meaning

The terms "high-level" and "low-level" are inherently relative. Some decades ago, the C language, and similar languages, was most often considered "high-level", as it supported concepts such as expression evaluation, parameterised recursive functions, and data types and structures, while assembly language was considered "low-level". Many programmers today might refer to C as low-level, as it lacks a large runtime-system (no garbage collection etc), basically supports only scalar operations, and provides direct memory addressing. It therefore readily blends with assembly language and the machine level of CPUs and microcontrollers.

Also note that assembly language may itself be regarded as a higher level (but still one-to-one) representation of machine code, as it supports concepts such as constants and (limited) expressions, sometimes even variables, procedures, and data structures. Machine code, in its turn, is inherently at a slightly higher level than the microcode or micro-operations used internally in many processors. See [http://c2.com/cgi/wiki?HighLevelLanguage C2's page about high-level languages] .

Execution models

There are three models of execution for modern high-level languages:;Interpreted :Interpreted languages are read and then executed directly, with no compilation stage.;Compiled :Compiled languages are transformed into an executable form before running. There are two types of compilation::;Intermediate representations :When a language is compiled to an intermediate representation, that representation can be optimized or saved for later execution without the need to re-read the source file. When the intermediate representation is saved it is often represented as bytecode.:;Machine code generation :Some compilers compile source code directly into machine code. Virtual machines that execute bytecode directly or transform it further into machine code have blurred the once clear distinction between intermediate representations and truly compiled languages.;Translated :A language may be translated into a low-level programming language for which native code compilers are already widely available. The C programming language is a common target for such translators.

ee also

* Abstraction (computer science)
* Low-level programming languages
* Very high-level programming languages
* Categorical list of programming languages

External links

* http://c2.com/cgi/wiki?HighLevelLanguage - The WikiWikiWeb's article on high-level programming languages

References