Hacker News Reader

Comment by Dewie | Hacker News Reader

> type Kilogram = Double

type synonym/alias.

In Haskell? I wouldn't do that. That improves readability, but it doesn't allow the compiler to enforce correct unit usage. If a Kilogram is just a synonym for a Double, you can pass it in where other meanings of Double are expected. E.g. you can pass Kilograms into a function that takes Pounds. Which you don't want to do.

Yeah no kidding. I brought it up to show that you can have the same kind of thing that skybrian was talking about in Haskell.

That's why you want

    newtype Kilogram = Kilogram Double

which has no runtime overhead but does enforce the fact the Kilogram is a distinct type.

We probably wanna add to it to make it useful

    {-# LANGUAGE GeneralizedNewtypeDeriving #-}
   
    newtype Kilogram = Kilogram Double deriving (Show, Eq, Ord, Num, Real, Fractional, Floating, ...)

And remind ourselves that Haskell is really quite expressive.

Though unfortunately can't handle (mass * accel :: Newton) without swapping out the Prelude.

Ada does it all.

My point was that named types in Go are not type aliases like in other languages.

Reply on news.ycombinator.com