Because #Funktal uses postfix expressions, there is no need for parentheses to group subexpressions. So I use the parentheses to delimit lambda functions. That is perhaps counter-intuitive but I prefer it over, say, [] or {}.

Funktal is strict, so any function gets applied right away. And it supports lambdas without arguments. So you can write something like

( 6 7 * )

and it will do the same as

6 7 *

but the parenthesised version is a function application.