Refine binary predefined function calls

Binary predefined calls always require parentheses due to left recursion and ambiguity issues, e.g. in id = ( 1 + 1 ) , the parentheses are required. It should be possible to specify top-level expressions without parentheses, e.g. id = 1+1, but multiple expressions will require parentheses still, e.g. id = 1 + (1 + 1) (or grouping the first two instead id = (1 + 1) + 1). The possibility to use parentheses should be retained for compatibility.