Roman numerals/Decode

# title: Roman numerals/Decode
# source: https://rosettacode.org/wiki/Roman_numerals/Decode
# category: Rosetta Code
# difficulty: Easy
# summary: Convert a Roman numeral string back to its integer value.
# tags: popular, strings, math, conversion
# vibe: 0.2

def roman_value(char)
  if char == "M"
    return 1000
  elsif char == "D"
    return 500
  elsif char == "C"
    return 100
  elsif char == "L"
    return 50
  elsif char == "X"
    return 10
  elsif char == "V"
    return 5
  elsif char == "I"
    return 1
  end
  0
end

def from_roman(roman)
  total = 0
  i = 0

  while i < roman.length
    current = roman_value(roman.slice(i))
    if i + 1 < roman.length
      next_val = roman_value(roman.slice(i + 1))
      if current < next_val
        total = total + (next_val - current)
        i = i + 2
      else
        total = total + current
        i = i + 1
      end
    else
      total = total + current
      i = i + 1
    end
  end

  total
end

def run
  {
    i: from_roman("I"),
    iv: from_roman("IV"),
    xlii: from_roman("XLII"),
    xcix: from_roman("XCIX"),
    mmxxiv: from_roman("MMXXIV")
  }
end