Custom Function - how to reference the column

[#1]

It is cool that custom functions can be used as well as part of custom formulas in Formula Editor.

With the Transform Category command, the 

New Custom Function( "myNamespace", "Add Ten", Function( {x, y = 10}, x + y ),  << Transform Category( "Custom" ));

from https://www.jmp.com/support/help/en/16.2/#page/jmp/create-custom-functions-transforms-and-formats.sh...

will show up in the right click New Formula Column Menu - and produce a column with formula

I just started with @txnelson 's approach 
https://community.jmp.com/t5/Discussions/Formula-for-Number-of-Unique-Categories-in-Column/m-p/55284... 
to generate a column to  Count Unique values - but instead of typing the formula, I wanted to use a Custom Function.

The manually generated Formula Column works, but the column that uses the Custom Function count unique doesn't.

It fails with the error message

Seems that x in the by() expression is not replaced with the column name.

So, use Eval(Substitute() to fix the issue?
... but how?

With

Eval(Substitute(Expr(Summarize( values = by( _col_ ) )),Expr(_col_),Name Expr(x) ));

I get

- because in a Column Formula :x is treated as :x[row()]. Argh ...

Along this line, I start to wonder why does this work:

[NB: the red zig-zag line just tells the user that print in a column formula is not a good idea]

 why does Jmp know that it has to send get values to the COLUMN :sex and and not to :sex[row()].
And why does it actually return :sex[row()] in the second line - and not the column :sex ?

Names Default To Here( 1 );
dt = Open( "$SAMPLE_DATA/Big Class.jmp" );

Add Custom Functions(
	New Custom Function(
		"custom",
		"count unique",
		Function( {x},
			As Constant( Summarize( values = by( x ) ) );
			N Items( values );
		),
		<<Transform Category( "Custom" ),
		<<Description( "count unique values" )
	)
);

New Column( "functionColumn",
	Formula(
		As Constant( Summarize( values = by( :sex ) ) );
		N Items( values );
	)
); //works

New Column( "customFunctionColumn", Formula( custom:count unique( :sex ) ) ); //doesn't work

[#2]

Hello @hogi ,

I'm not sure if this is a smart approach, but the following script works. I used eval insert function. I hope it helps.

Names Default To Here( 1 );
dt = Open( "$SAMPLE_DATA/Big Class.jmp" );

Add Custom Functions(
	New Custom Function(
		"custom",
		"count unique",
		Function( {x},
			Eval( Parse( Eval Insert( "As Constant( Summarize( values = by( :^x^ ) ) )" ) ) );
			N Items( values );
		),
		<<Transform Category( "Custom" ),
		<<Description( "count unique values" )
	)
);

New Column( "customFunctionColumn", Formula( custom:count unique( "sex" ) ) ); 

[#3]

hm, unfortunately, it doesn't work:

produces the error message:

So, the same as like with

Substitute (..., Expr(_col_),Name Expr(x))

I guess it's because a function call to make it work has to be  

custom:count unique( "sex" )

instead if 

custom:count unique( :sex )

[#4]

I just found an earlier (2018) version of the same question:

Column reference in custom function 

[#5]

The quite definite reply from Jmp Support TS-00063463