High-level programming language
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A high-level programming language is a programming language that, in comparison to low-level programming languages, may be more abstract, easier to use, or more portable across platforms. Such languages often abstract away CPU operations such as memory access models and management of scope.
Features of high-level languages
The term "high-level language" does not imply that the language is always superior to low-level programming languages - in fact, in terms of depth of knowledge of how computers operate the inverse may in fact 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 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 languages like Assembly language. Other features such as string handling routines, object-oriented language features and file input/output may also be present.
Stereotypically, high-level languages make complex programming simpler, while low-level languages tend to produce more efficient code. In a high-level language, complex elements can be broken up into simpler, though still fairly complex, elements for which the language provides abstractions, keeping programmers from having to "reinvent the wheel." 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 more efficient code than most low-level programmers can do by hand.
Note that the terms "high-level" and "low-level" are inherently relative. Originally, assembly language was considered low-level and COBOL, C, etc. were considered high-level, as they allowed the abstractions of functions, variables and expression evaluation, and also that they had to be compiled to assembly before being compiled into machine code. Many programmers today might refer to C as low-level, as it still allows memory to be accessed by address, and provides direct access to the assembly level. For more on this distinction, see C2's page about high-level languages.
There are three models of execution for modern high-level languages:
- Interpreted languages are read and then executed directly, with no compilation stage.
- 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 byte code.
- Machine code generation
- Some languages compile directly into machine code (or assembly language). 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.
- 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.
- Low-level programming languages
- Medium-level programming languages
- Very high-level programming languages
- Categorical list of programming languages
- http://c2.com/cgi/wiki?HighLevelLanguage - The WikiWikiWeb's article on high-level programming languages