"foo"
     : string
match "a" with
| "a" => true
| _ => false
end
     : bool
String (Ascii.Ascii false true true false false true true false)
  (String (Ascii.Ascii true true true true false true true false)
     (String (Ascii.Ascii true true true true false true true false)
        EmptyString))
     : string
match
  String (Ascii.Ascii true false false false false true true false)
    EmptyString
with
| String (Ascii.Ascii true false false false false true true false)
  EmptyString => true
| _ => false
end
     : bool
