Assembly languages directly correspond to a machine language (see below) in order to allow machine code instructions to be written in a form understandable by humans. Assembly languages allow programmers to use symbolic addresses which are later converted to absolute addresses by the assembler. Most assemblers also allow for macros and symbolic constants.
Message passing languages provide language constructs for concurrency. The predominant paradigm for concurrency in mainstream languages such as Java is shared memory concurrency based on monitors. Concurrent languages that make use of message passing have generally been inspired by CSP or the π-calculus, but have had little commercial success, except for Ada and Erlang. Ada is a multipurpose language and concurrent programming is only one option available.
Dataflow programming languages rely on a (usually visual) representation of the flow of data to specify the program. Frequently used for reacting to discrete events or for processing streams of data. Examples of dataflow languages include:
Data-oriented languages provide powerful ways of searching and manipulating the relations that have been described as entity relationship tables which map one set of things into other sets. Examples of data-oriented languages include:
Declarative languages describe a problem rather than defining a solution. Declarative programming stands in contrast to imperative programming via imperative programming languages, where serial orders (imperatives) are given to a computer. In addition to the examples given just below, all (pure) functional and logic-based programming languages are also declarative. In fact, "functional" and "logical" constitute the usual subcategories of the declarative category.
Functional programming languages define programs and subroutines as mathematical functions. Many so-called functional languages are "impure", containing imperative features. Not surprisingly, many of these languages are tied to mathematical calculation tools. Functional languages include:
Interpreted languages are programming languages which programs may be executed from source code form, by an interpreter. Theoretically, any language can be compiled or interpreted, so the term *interpreted language* generally refers to languages that are commonly interpreted rather than compiled.
Machine languages are directly executable by a computer's CPU. They are typically formulated as bit patterns, usually represented in octalor hexadecimal. Each group of npatterns (often 1 or more bytes) causes the circuits in the CPU to execute one of the fundamental operations of the hardware. The activation of specific electrical inputs (eg, CPU package pins for microprocessors), and logical settings for CPU state values, control the processor's computation. Individual machine languages are processor specific and are not portable. They are (essentially) always defined by the CPU developer, not by 3rd parties. The symbolic version, the processor's assembly language, is also defined by the developer, in most cases. Since processors come in families which are based on a shared architecture, the same basic assembly language style can often be used for more than one CPU. Each of the following CPUs served as the basis for a family of processors:
Metaprogramming is writing of programs that write or manipulate other programs (or themselves) as their data or that do part of the work that is otherwise done at run time during compile time. In many cases, this allows programmers to get more done in the same amount of time as they would take to write all the code manually.
Procedural programming languages are based on the concept of the unit and scope (the data viewing range of an executable code statement). A procedural program is composed of one or more units or modules, either user coded or provided in a code library; each module is composed of one or more procedures, also called a function, routine, subroutine, or method, depending on the language. Examples of procedural languages include:
Reflective languages let programs examine and possibly modify their high level structure at runtime. This is most common in high-level virtual machine programming languages like Smalltalk, and less common in lower-level programming languages like C. Languages and platforms supporting reflection:
Rule-based languages instantiate rules when activated by conditions in a set of data. Of all possible activations, some set will be selected and the statements belonging to those rules will be executed. Examples of rule-based languages include:
"Scripting language" has two apparently different, but in fact similar meanings. In a traditional sense, scripting languages are designed to automate frequently used tasks that usually involve calling or passing commands to external programs. Many complex application programs allow users to implement custom functions by providing them with built-in languages. Those which are of interpretive type, are often called scripting languages.
More recently many of these applications have chosen to "build in" traditional scripting languages, such as Perl or Visual Basic, but there are quite a few "native" scripting languages still in use. Many scripting languages are compiled to bytecode and then this (usually) platform independent bytecode is run through a virtual machine (compare to Java).
These are languages based on or that operate on XML. Although the big-boy equivalents of Oracle/PostgreSQL/MSSQL don't yet exist for XML, there are languages to navigate through it and its more tree-oriented structure.