Hi all,
I was trying to do some Elm Voodoo and I stumbled upon a funny thing. It is
probably deeply wrong, but I want to understand why it is wrong :-)
What I was trying to do was to define a type like this:
type alias Convertor a =
{ convert : b -> a
}
Here I get "Type alias `Convertor` must declare its use of type variable b"
Now, I understand, why you cannot have
type alias X a = { field1: a, field2: b }
But with the source type of functions, things are IMHO different than with
values. You cannot write values of unbound types and you could not decide
whether two instances of X are really the same type.
But you can easily write functions that have unbound source types - like
this one:
convertString: a -> String
convertString x =
(toString x) ++ "_Foo"
And since all of functions with this signature really have the same type at
JavaScript level, two instances of 'Convertor a' would always had the same
type.
Now if I had
c: Convertor String
c = {convert = convertString}
the whole thing seems type-safe...
So my question is:
Is this syntax forbidden, because it is an obscure feature that is not
worth supporting, or would this syntax really allow for some type unsafe
code?
Thanks!
Martin
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