User Defined Functions with Expression arguments

[#1]

In JSL there are many functions which allow Expressions as arguments, like

dt << New Column( "X", Formula( row() ) );

where the supplementary argument Formula( row() ) can be at any position (N>1) within (...) because it can be identified via the keyword 

Formula().

Can user-defined functions have similar supplementary arguments?

[#2]

No. The user defined function always evaluates the arguments that were passed before putting the values into its local parameters.

You could use expr(), but a list is a better choice: myfunc( "X", { formula( row() ) } ). I used that somewhere recently, and it worked well; variables inside the list still need to be evaluated, and myfunc finds them in the proper calling context. (Assuming no collisions between the caller names and myfunc names...) I think I used a single list and took advantage of nitems() as well.

[#3]

Thanks @Craige_Hales , the workaround with the list - brilliant

Hm, worth to write a post for the wish list?

Ah, there is one:
Keyword arguments for functions