middle_three_digits = proc (n: int) returns (string)
                      signals (too_small, even_length)
    s: string := int$unparse(int$abs(n))
    if string$size(s) < 3 then signal too_small end
    if string$size(s) // 2 = 0 then signal even_length end
    return(string$substr(s, string$size(s)/2, 3))
end middle_three_digits

start_up = proc ()
    po: stream := stream$primary_output()
    tests: sequence[int] := sequence[int]$
        [123,12345,1234567,987654321,10001,-10001,-123,-100,100,-12345,
         1,2,-1,-10,2002,-2002,0]

    for test: int in sequence[int]$elements(tests) do
        stream$putright(po, int$unparse(test) || ": ", 11)

        stream$putl(po, middle_three_digits(test))
        except
            when too_small: stream$putl(po, "Too small")
            when even_length: stream$putl(po, "Even length")
        end
    end
end start_up