I can't pass a variable as parameter to a function

[etardiff]

@vuk

<$let p=2>
{{{ [.myfun[<p>]] }}}
</$let>

You’ve got too many brackets — try [.myfun<p>] instead.

Those Pesky Brackets is a good reference for when to use each type of bracket — but the super-short rule is that you should never be nesting them inside a filter.

tag[literal name of the tag]
tag<variable>
tag[<variable>]
tag{!!fieldname}
tag[{!!fieldname}]

(@Brian_Radspinner, I’m noticing that all your examples are things like <$list filter="[<stuff>]" /> — great as a minimal testcase! But it occurs to me that it might be useful to include things like <$list filter="[tag<stuff>]" /> as well, so it’s more obvious how variables/transclusions are intended to work with filter operators.)