matasar

def n5s(str)
  first, num, last = str.match(/([a-zA-Z])(\d+)([a-zA-Z])/).captures
  num = num.to_i
  puts open("/usr/share/dict/words").grep(/\b#{first}[a-zA-Z]{#{num}}#{last}\b/)
end

> n5s("i18n")
institutionalization
intercrystallization
interdifferentiation

kourge

operator prefix ~ {}

@prefix func ~(pattern: String) -> NSRegularExpression! {
    var error: NSError?
    return NSRegularExpression.regularExpressionWithPattern(
        pattern,
        options: nil,
        error: &error)
}