roman = cluster is decode
    rep = null

    digit_value = proc (c: char) returns (int) signals (invalid)
        if c < 'a' then c := char$i2c(char$c2i(c) + 32) end
        if     c = 'm' then return(1000)
        elseif c = 'd' then return(500)
        elseif c = 'c' then return(100)
        elseif c = 'l' then return(50)
        elseif c = 'x' then return(10)
        elseif c = 'v' then return(5)
        elseif c = 'i' then return(1)
        else signal invalid
        end
    end digit_value

    decode = proc (s: string) returns (int) signals (invalid)
        acc: int := 0
        for i: int in int$from_to(1, string$size(s)) do
            d: int := digit_value(s[i])
            if i < string$size(s) cand d < digit_value(s[i+1]) then
                acc := acc - d
            else
                acc := acc + d
            end
        end resignal invalid
        return(acc)
    end decode
end roman

start_up = proc ()
    po: stream := stream$primary_output()
    tests: array[string] := array[string]$
        ["MCMXC", "mdclxvi", "MmViI", "mmXXi", "INVALID"]

    for test: string in array[string]$elements(tests) do
        stream$puts(po, test || ": ")
        stream$putl(po, int$unparse(roman$decode(test))) except when invalid:
            stream$putl(po, "not a valid Roman numeral!")
        end
    end
end start_up