created: 20150220181617000 modified: 20150221221642000 tags: WikiText title: Macro Definitions in WikiText type: text/vnd.tiddlywiki caption: Macro Definitions A [[macro|Macros]] is defined using a `\define` [[pragma|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: <$codeblock code={{$:/editions/tw5.com/macro-examples/say-hi}}/> 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|Macro Definition Syntax]] 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|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: <$importvariables filter="$:/editions/tw5.com/macro-examples/say-hi-using-variables"> <$codeblock code={{$:/editions/tw5.com/macro-examples/say-hi-using-variables}}/> <$macrocall $name=".example" n="1" eg="""<$set name="address" value="Rabbit Hole Hill"> <> """/> !! 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 <<.tag $:/tags/Macro>>. It is also possible to write a macro as a [[JavaScript module|http://tiddlywiki.com/dev/index.html#JavaScript%20Macros]]. ~JavaScript macros are available to all tiddlers, and offer the maximum flexibility. A tiddler can manually import macro definitions from a [[selection|Title Selection]] of other tiddlers by using the <<.wlink ImportVariablesWidget>> widget.