Abstract syntax: N elem-of Nml = binary numerals

    N ::= I . F
    I ::= B | I B
    F ::= B | B F
    B ::= 0 | 1

Semantic domain: Z = real numbers

Semantic function: Nm: Nml -> Z

    Nm[[I . F]] = Nm[[I]] + Nm[[F]]
    Nm[[I B]] = 2*Nm[[I]] + Nm[[B]]
    Nm[[B F]] = Nm[[B]] + Nm[[F]]/2
    Nm[[0]] = 0
    Nm[[1]] = 1