I want to parse expressions such that the resulting parse trees are of the form:

#(BIN_OP left op right)

For "a+b-1", I want to see:

#(BIN_OP #(BIN_OP a PLUS b) MINUS 1)

I have the following code:

			
				

				exp7 :
				

				exp8 ( binop7 exp8
				

				{ #exp7 = #([BIN_OP, "BIN_OP"], exp7); } )*
				

				;
				

				

			
		

However, after assigning to #exp7, subsequent children are added to the right of the last child, which is not what I want. I get instead:

#(BIN_OP #(BIN_OP a PLUS b MINUS 1))

Since the documented behavior of assigning to #exp7 is not what I want, how do I construct this tree, such that the snippet in ( )* works properly? (Note: if I don't have ( )* then I do get an imaginary parent. This is well documented with plenty of examples.)