Binary to Decimal

Implement BinaryToDecimal<S> which takes an exact string type S consisting 0 and 1 and returns an exact number type corresponding with S when S is regarded as a binary.
You can assume that the length of S is equal to or less than 8 and S is not empty.

type Res1 = BinaryToDecimal<'10'>; // expected to be 2
type Res2 = BinaryToDecimal<'0011'>; // expected to be 3