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Shelf heralds
Prerequisite Concepts

Heralds are keywords that precede a variable name and indicate its type.

Versions of OmniMark prior to V3 required all uses of a shelf or pattern name to be heralded to indicate the variable type. This allowed programmers to omit variable declarations for small simple programs.

OmniMark V3 requires variable declarations so that heralds may be omitted. This is more useful for larger programs where variable declarations are often present anyway.

OmniMark V3 can run V2 programs when the declare heralded-names declaration is placed after the translation type using the -herald command-line argument.

The following can be used as heralds:

• shelf types counter, switch, and stream
• opaque type names declared with declare opaque
• pattern for pattern variables
• some actions

Type heralds are always required, even with V3:

• before the built-in sgml-error rule pattern variables class, message, additional-info, recovery-info, file-name, and line-number
• in global and local shelf declarations
• before variable names that are quoted.

Type heralds are always prohibited after any action keyword that behaves as a type herald, even with V2. (In other words, it is illegal to herald a variable name twice.) These keywords are:

• open
• reopen
• put
• discard
• output-to
• using output as
• activate
• deactivate
• reset

In all other cases, type heralds are required when:

• declare heralded-names is specified
• -herald is specified on the command line
• OmniMark V2 or an earlier release is used

If none of the above cases apply, type heralds are optional.

Prerequisite Concepts      Arrays    Heralds

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