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High-Level Language

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High-Level Language

In computer science, 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 may automate (or even hide entirely) significant areas of computing systems (e.g. memory management), making the process of developing a program simpler and more understandable relative to a lower-level language. The amount of abstraction provided defines how "high-level" a programming language is.[1] Examples of high-level programming languages include FOCUS, Lisp, Perl, Python, Ruby, SAS, and COBOL.

The first high-level programming language designed for computers was Plankalkül, created by Konrad Zuse.[2] However, it was not implemented in his time, and his original contributions were largely isolated from other developments (it influenced Heinz Rutishauser's language "Superplan").

In the 1960s, high-level programming languages using a compiler were commonly called autocodes.[3] Examples of autocodes are COBOL and Fortran.[4]

Features

"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 variables, arrays, objects, complex arithmetic or boolean expressions, subroutines and functions, loops, threads, locks, and other abstract computer science concepts, with a focus on usability over optimal program efficiency. Unlike low-level assembly languages, high-level languages have few, if any, language elements that translate directly into a machine's native opcodes. Other features, such as string handling routines, object-oriented language features, and file input/output, may also be present.

Abstraction penalty

While high-level languages are intended to make complex programming simpler, low-level languages often produce more efficient code. Abstraction penalty is the border that prevents high-level programming techniques from being applied in situations where computational resources are limited. High-level programming exhibits features like more generic data structures, run-time interpretation, and intermediate code files; which often result in slower execution speed, higher memory consumption, and larger binary program size.[5][6][7] For this reason, code which needs to run particularly quickly and efficiently may require the use of a lower-level language, even if a higher-level language would make the coding easier. In many cases, critical portions of a program mostly in a high-level language can be hand-coded in assembly language, leading to a much faster or more efficient optimised program.

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 hand, and the higher abstraction may allow for more powerful techniques providing better overall results than their low-level counterparts in particular settings.[8] High-level languages are designed independent of structure of a specific computer. This facilitates executing a program written in such a language on different computers.

Relative meaning

The terms high-level and low-level are inherently relative. Some decades ago, the C language, and similar languages, were 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". Today, many programmers 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.

Assembly language may itself be regarded as a higher level (but often still one-to-one if used without macros) 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.

Execution models

There are three general models of execution for modern high-level languages:

Interpreted 
Interpreted languages are read and then executed directly, with no compilation stage. A program called an interpreter reads each program statement following the program flow, decides what to do, and does it. A hybrid of an interpreter and a compiler will compile the statement into machine code and execute that; the machine code is then discarded, to be interpreted anew if the line is executed again. Interpreters are commonly the simplest implementations, compared to the other two variants listed here.
Compiled 
Compiled languages are transformed into an executable form before running. There are two types of compilation:
Machine code generation 
Some compilers compile source code directly into machine code. This is the original mode of compilation, and languages that are directly and completely transformed to machine-native code in this way may be called "truly compiled" languages. See assembly language.
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 byte code. The intermediate representation must then be interpreted or further compiled to execute it. Virtual machines that execute byte code 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 lower-level programming language for which native code compilers are already widely available. The C programming language is a common target for such translators. See Chicken Scheme.

Note that languages are not strictly "interpreted" languages or "compiled" languages. Rather, language implementations use interpretation or compilation. For example, Algol 60 and Fortran have both been interpreted (even though they were more typically compiled). Similarly, Java shows the difficulty of trying to apply these labels to languages, rather than to implementations; Java is compiled to bytecode and the bytecode is subsequently executed by either interpretation (in a JVM) or compilation (typically with a just-in-time compiler such as HotSpot, again in a JVM).

See also

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Computer programming portal

References

External links

  • WikiWikiWeb's article on high-level programming languages

Template:Programming language

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