String literal typing appears to be a common feature of type systems bolted onto dynamic languages:

    # Python
    MyStringBool = Literal("Yes") | Literal("No")

    // TypeScript
    type MyStringBool = "Yes" | "No"

It would seem pretty unnecessary in Haskell, where you can just define whatever types you want without involving strings at all:

    data MyBool = Yes | No

    parseMyBool :: String -> MyBool 
    parseMyBool "Yes" = Yes
    parseMyBool "No" = No
    parseMyBool _ = error "..."

    @type my_bool() :: :yes | :no

    @spec parse_my_bool(String.t()) :: my_bool()
    def parse_my_bool("Yes"), do: :yes
    def parse_my_bool("No"), do: :no
    def parse_my_bool(_), do: throw("...")