Here is a piece of code that works:
nr=5;
new window("Button test",
	Lineuplist=Lineup Box( N Col( 2 ),
		
	)
);
For(i=1,i<=nr,i++,
	Lineuplist << append(textbox("Text nr "||char(i)));
	Lineuplist << append(
		buttonbox("Button nr "||char(i),
			<< Set Function(
				Function({this},
					ps=this<<sib;
					par=this<<parent;
					buttonName=this<<get button name;
					buttonNo=regex(buttonName,".*?([0-9]*)$","\1");
					locator=eval insert("//TextBox[text()='Text nr ^buttonNo^']");
					textBox=par<<xpath(locator);
					textBox<<delete;
					this<<delete;
				)
			)
		);
	);
);