{{alias}}( s1, s2 )
    Calculates the Hamming distance between two equal-length input strings.

    The function returns a sentinel value of -1 if the input string lengths
    differ.

    Parameters
    ----------
    s1: string
        First input string.

    s2: string
        Second input string.

    Returns
    -------
    out: number
        Hamming distance.

    Examples
    --------
    > var d = {{alias}}( 'algorithms', 'altruistic' )
    7
    > d = {{alias}}( 'elephant', 'hippopod' )
    7
    > d = {{alias}}( 'javascript', 'typescript' )
    4
    > d = {{alias}}( 'levenshtein', 'levitations' )
    8
    > d = {{alias}}( 'sacrifice', 'paradisal' )
    8

    See Also
    --------