from-octal (See related posts)

    from-octal: func [
        "Converts an octal number to a decimal value."
        octal [any-string! integer!]
        /local result len
    ][
        result: 0
        octal: form octal
        repeat i len: length? octal [
            result: add result (to integer! form octal/:i) * (8 ** (len - i))
        ]
        any [attempt [to integer! result] result]
    ]