< EBNF >
Expr ::= Term([+|-] Expr)?
Term ::= Factor ([*|/] Term)?
Factor :: = (Expr)
| Value
Value ::= Integer | Double
< >
Expr ::= Term
(s) expr.isDouble = term.isDouble
(i) term.type = if expr.isDouble then double else int
Expr1 ::= Term [+-] Expr2
(s) expr1.isDouble = term.isDouble or expr2.isDouble
(i) term.type = expr1.isDouble then double else int
(i) expr2.type = expr1.isDouble then double else int
Factor ::= (Expr)
(s) factor.isDouble = expr.isDouble
(i) expr.type = factor.isDouble then double else int
Factor ::= Value
(s) factor.isDouble = value.isDouble
(i) value.type = factor.isDouble then double else int
Value :: Decimal Integer
(s) value.isDouble = false
(i) value.type = value.type == double then double else int
Value :: Double
(s) value.isDouble = true
(i) value.type = value.type == double then double else int
