New in: 5.1.20The conditional filter operators allow if-then-else logic to be expressed within filters.
The foundation is the convention that an empty list can be used to represent the boolean value false and a list with at one (or more) entries to represent true.
The conditional operators are:
[[HelloThere]is[missing]then[FOO]]
evaluates to (empty)[[Missing Tiddler]is[missing]then[FOO]]
evaluates to FOO
[[HelloThere]is[tiddler]else[BAR]]
evaluates to HelloThere
[[Missing Tiddler]is[tiddler]else[BAR]]
evaluates to BAR
These operators can be combined. For example:
[[New Tiddler]is[missing]then[I am missing]else[No I am not missing]]
evaluates to I am missing
The else Operator can be used to apply a defaults for missing values. In this example, we take advantage of the fact that the get Operator returns an empty list if the field or tiddler does not exist:
[[HelloThere]get[custom-field]else[default-value]]
evaluates to default-value