This is an implementation of the Roman numeral Kata, inspired by the novel Gadsby by Ernest Vincent Wright. It does not use the letter E.

roman.rb

MAP = [['M', 1000], ['D', 500], ['C', 100], ['L', 50], ['X', 10], ['V',5], ['I',1]]

prv = proc { |i|
  t = MAP.map(&:first)
  t.zip(t.drop(1)).rassoc(i).first
}

sub = proc { |string|
  string.gsub(/(.)?(.)(\2){3}/) { |_|
    output = nil
    output = $2 + prv[$2] if not $1
    output = $2 + prv[$1] if $1 and prv[$2] == $1
    output = $1 + $2 + prv[$2] if $1 and prv[$2] != $1
    output
  }
}

do_it = proc { |arabic|
  cons = MAP.find {|c| c.last <= arabic}
  arabic == 0 ? "" : cons.first + do_it[arabic - cons.last]
}

catch(:quit) {
  loop {
    arabic = ARGF.first
    throw(:quit) if ! arabic
    arabic = arabic.to_i
    puts arabic
    puts sub[do_it[arabic]]
    # 1 last thing:
    ARGF.first
  }
}

spc.sh

ruby roman.rb spc.txt | diff -u spc.txt - && printf 'Good!\n'
grep -i e roman.rb

spc.txt

1
I
2
II
7
VII
9
IX
40
XL
140
CXL
3999
MMMCMXCIX