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Function types and anatomy
Prerequisite Concepts		Related Syntax

An OmniMark program can define two different kinds of functions:

• Internal functions are defined completely in OmniMark.
• External functions have an interface that is defined in OmniMark, and an implementation that is defined in another programming language.

Internal functions serve the following purposes:

• To encapsulate a code sequence that is executed in more than one place.
• To increase readability by supplying a name and an explicit parameterization to a complex sequence of code.

External functions are used to gain access to external applications or operating system services which are not available directly in OmniMark.

There are two aspects to a function:

• The function definition defines the interface and, for internal functions, provides the implementation of the function. For external functions, the function definition defines the interface, the name of the external function, and the external function library which provide the implementation.
• The function call causes the function to be executed.

Additionally, a function may have a function predefinition which simply defines the function interface.