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nesarkvechnep • yesterday at 9:37 PM • 2 replies • view on HN

I guess C# is more strongly-typed than Haskell then... /s

Replies

troad • today at 12:05 AM

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"
I assume it exists to compensate for the previous lack of typing, and consequent likelihood of ersatz typing via strings.

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
Of course you'd need a trivial parser, though this is probably a good idea for any string type:

    parseMyBool :: String -> MyBool 
    parseMyBool "Yes" = Yes
    parseMyBool "No" = No
    parseMyBool _ = error "..."
Interestingly, dynamic languages which make use of symbols (Ruby, Elixir, Common Lisp) probably fall closer to Haskell than Python or TS. Elixir example:

    @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("...")
Where :yes and :no are memory-efficient symbols, not strings.
goto11 • yesterday at 11:29 PM

You cant have a `type Foo = String | Strimg` in Haskell either.