Passing a Variable to an Action Macro

Tips & Tricks
#1

As discussed in this thread, here is a piece of TW syntax lore that may not be very obvious.

The $macrocall documentation tells us that

Macro parameters are specified as widget attributes, thus allowing indirection via {{title!!field}}, <<macroname>> or {{{filter}}}

However, this does not work directly when the macro call is used in the action attribute of various widgets. Instead, you have to wrap it in triple double quotes, like so:

\define clickactions(text)
<$action-sendmessage $message="tm-notify" $param=<<__text__>> />
\end

<$let variable="SampleNotification">
  <$button actions="""<$macrocall $name="clickactions" text=<<variable>> />""" >
    Click Me
  </$button>
</$let>

@EricShulman explained it in the context of the $button widget like this:

[With triple double quotes, the] macrocall is defined as literal text that is only invoked (and wikified) when the $button widget is actually clicked. Thus, a true macro call is occurring.

Without the triple quotes, the macrocall is simply replaced by the text of the macro when the $button widget is rendered, so that any macro parameters have no meaning.

Have a nice day
Yaisog

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#2

The tripple double-quotes are only needed, because the <$macrocall $name="clickactions" text=<<variable>> /> also contains a single double-quote character. So the parser needs the tripple quotes to know where the start and end of the string is

#3

The significance of this syntax is that it is not obvious and not explained in the documentation (at least of the ButtonWidget).

The “usual” behavior when putting a macro call into (triple) quotes is that it remains a literal string and unevaluated, e.g.

<$let variable="""<$macrocall $name="now" format="YYYY-0MM-0DD" />""">
  <$text text=<<variable>> /><br>
  <$text text="""<$macrocall $name="now" format="YYYY-0MM-0DD" />""" />
</$let>

will twice yield the string <$macrocall $name="now" format="YYYY-0MM-0DD" />, but not today’s date.
When used in the actions attribute, however, that string is being evaluated (albeit only when the actions are initiated).

That was the reason why – at least for me – that little gem went undiscovered until Eric posted about it.

Have a nice day
Yaisog

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