I’m trying to dutifully use tagged types instead of, say, `Float`:
type DropsPerSecond
= DropsPerSecond Float
It turns out I want to know which of two `DropsPerSecond` is larger. Which
suggests this:
(>) : DropsPerSecond -> DropsPerSecond -> Bool
(>) (DropsPerSecond left) (DropsPerSecond right) =
left > right
However, that produces this error message:
> The left argument of (>) is causing a type mismatch.
>
> 18| left > right
> ^^^^
> (>) is expecting the left argument to be a:
>
> DropsPerSecond
>
> But the left argument is:
>
> Float
This doesn’t happen if I use `(<><>)` instead of `(>)`. Nor does it happen if I
use `gt`.
Help me understand?
—————
Somewhat related is this question: is this the right way to tag types?
—————
Also: I’m finding these types fairly awkward to work with, in that I have
functions that want to operate on the base type and also the wrapping type
(typically to pass work to other functions). It seems to me that means I have
to do things like this semi-contrived example:
animationSteps dropsPerSecond =
let
(DropsPerSecond raw) = dropsPerSecond
in
if raw > 8.0 then
steadyStream
else
fallingDrop dropsPerSecond
Given decent tests (which I’m good at), I’m dubious that all this work to avoid
the relatively small chance of confusing a-float-that-means-duration with
a-float-that-means-rate is cost-effective. However, I am intent on going all-in
on “the Elm/Haskell way”, so I’m curious whether I’m approaching this all
wrong. Also happy to hear experienced people tell me that the extra work does
indeed pay off.
--
You received this message because you are subscribed to the Google Groups "Elm
Discuss" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to [email protected].
For more options, visit https://groups.google.com/d/optout.
