
program = [ " v1 = " expr ";" ]
          [ " v2 = " expr ";" ]
          [ " v3 = " expr ";" ]        
          [ " v4 = " expr ";" ]
          [ " v5 = " expr ";" ]
          "  y = " expr ";"

expr = expr op expr / 
       "(" expr op expr ")" /
       var

op = "+" / "-" / "/" / "*"

var = constant / "x[1]" / "x[2]" / "v1" / "v2" / "v3" / "v4" / "v5"
 
constant = decimal / neg-decimal

decimal = DIGIT "." 1*2DIGIT

neg-decimal = "(-" decimal ")"


