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Function predefinitions
Prerequisite Concepts		Related Syntax

No special provision is required when declaring a function that calls itself, but if two functions are written such that each calls the other, it is impossible to define each function prior to its first use: one must precede the other. To support such mutually recursive functions, OmniMark provides function "predefinitions". A function predefinition looks just like a function definition except that it has no body. Instead of as and a following set of local declarations and actions, there is just the keyword elsewhere.

For example:

  define function analyse-command-set (value stream command-set)
        elsewhere

Functions must be defined or predefined before they are used. For mutually recursive functions, one or more of the functions must be predefined prior to the first actual function definition.

Here are some rules for using function predefinitions:

• If a function is predefined, it must also be defined.
• A function can have more than one predefinition. Predefinitions can come after, as well as before, the function's definition.
• The definition and every predefinition for a function must use the same result type (or none in all cases) and the same set of arguments, in the same order, each with the same class, type and name.
• External functions must not be predefined. External functions are not actually defined in an OmniMark program, they are just declared.

Prerequisite Concepts      Function types and anatomy    Functions

Related Syntax    define function    elsewhere

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