oper $ gen prefix 50
oper $ gen infix none 50

def gen{a}{b,c} = __mul{a,__sub{b,c}}
def gen{a,b}{c} = __add{a,__mul{b,c}}

fn fun() : f64 = { 20 ${3} ${4,5} 2 }

fn fi() : f64 = {
  def o = ${4,5}
  (${3}){20, o{2}}
}