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## Macro Definitions in WikiText

21st February 2015 at 10:16pm

A macro is defined using a \define pragma. Like any pragma, this can only appear at the start of a tiddler.

The first line of the definition specifies the macro name and any parameters. Each parameter has a name, and optionally a default value that is used if no value is supplied on a particular call to the macro. The lines that follow contain the macro's text (i.e. the snippet represented by the macro name), until \end appears on a line by itself:

\define sayhi(name:"Bugs Bunny" address:"Rabbit Hole Hill")
Hi, I'm $name$ and I live in $address$.
\end


Alternatively, the entire definition can be presented on a single line, without an \end marker:

\define sayhi(name:"Bugs Bunny") Hi, I'm $name$.

A more formal presentation of this syntax is also available.

## Placeholders

The snippet can contain placeholders for parameters. These consist of a parameter name between dollar signs, like $this$.

It can also contain placeholders for variables. These consist of a variable name (or macro name) between dollar signs and round brackets, like $(this)$.

The actual value of the parameter or variable is substituted for the placeholder whenever the macro is called:

\define say-hi-using-variables()
Hi, I'm $(name)$ and I live in $(address)$.
\end

\define name() Bugs

<$set name="address" value="Rabbit Hole Hill"> <<say-hi-using-variables>> </$set>

## Scope

Macros are available to the tiddler that defines them, plus any tiddlers that it transcludes.

To make a macro available to all tiddlers, define it in a tiddler that has the tag $:/tags/Macro. It is also possible to write a macro as a JavaScript module. JavaScript macros are available to all tiddlers, and offer the maximum flexibility. A tiddler can manually import macro definitions from a selection of other tiddlers by using the $importvariables widget.