A concatenative programming language is a point-free computer programming language in which all expressions denote functions, and the juxtaposition of expressions denotes function composition.Concatenative programming replaces function application, which is common in other programming styles, with function composition as the default way to build subroutines.
For example, a sequence of operations in an applicative language like the following:
...is written in a concatenative language as a sequence of functions, without parameters:
foo bar baz
Functions and procedures written in concatenative style are not value level, i.e. they typically do not represent the data structures they operate on with explicit names or identifiers; instead they are function level - a function is defined as a pipeline, a sequence of operations that take parameters from an implicit data structure on which all functions operate, and return the function results to that shared structure so that it will be used by the next operator.
The combination of a compositional semantics with a syntax that mirrors such a semantics makes concatenative languages highly amenable to algebraic manipulation of programs;although it may be difficult to write mathematical expressions directly in them. Concatenative languages can be implemented in an efficient way with a stack machine, and are commonly present implicitly in virtual machines in the form of their instruction sets.
Much of the original work on concatenative language theory was carried out by Manfred von Thun.[ citation needed ]
The properties of concatenative languages are the result of their compositional syntax and semantics:
The first concatenative programming language was Forth, although Joy was the first language to call itself concatenative. Other concatenative languages are Factor, Onyx, PostScript, and RPL.
Most existing concatenative languages are stack-based; this is not a requirement and other models have been proposed.Concatenative languages are currently used for embedded, desktop, and web programming, as target languages, and for research purposes.
Most concatenative languages are dynamically typed. Exceptions include the statically typed Cat language.
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x = "foo", where
"foo" is a string literal with value
foo – the quotes are not part of the value, and one must use a method such as escape sequences to avoid the problem of delimiter collision and allow the delimiters themselves to be embedded in a string. However, there are numerous alternate notations for specifying string literals, particularly more complicated cases, and the exact notation depends on the individual programming language in question. Nevertheless, there are some general guidelines that most modern programming languages follow.
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In computer programming,
?: is a ternary operator that is part of the syntax for basic conditional expressions in several programming languages. It is commonly referred to as the conditional operator, inline if (iif), or ternary if. An expression
a? b : c evaluates to
b if the value of
a is true, and otherwise to
c. One can read it aloud as "if a then b otherwise c".
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