good morning
fn sum<A, F>(v: F) -> A where A: Monoid, A: Semigroup, F: Foldable<A, A=A> {
v.fold(A::mempty(), |b, a| A::mappend(&b, a))
}
is there a better way of saying that A: Monoid and Semigroup?
other than having to have the semigroup function be part of the Monoid
Are
Monoid and Semigroup independent, or does one require the other?
Monoid requires Semigroup
but Semigroup has teh mappend function and Monoid the mempty
A: Monoid + Semigroup
and what if they were independent?
just want to know the syntax change
thank you btw :)
Then you should probably define Monoid as
pub trait Monoid: Semigroup { ... }
monoid is defined that way
Then you shouldn't need to require
A: Semigroup specifically, as A: Monoid already implies that.
pub trait Semigroup: Clone {
fn mappend(self: &Self, other: &Self) -> Self;
}
pub trait Monoid: Semigroup {
fn mempty() -> Self;
}
it complains that mappend is not part of A
oh nvm
:/ it seems to be working now
maybe i was high when first testing it :)
thank you anyway
when you impl X for A does that mean that impl is now always in scope and i dont have to import it in some way?
@lemonxah you only need to have module with impl within your crate
so its almost like typeclasses?
Very similar
but let say i have a Show typeclass and i want multiple impl for the same type but i want to choose which one is in scope?
No. You can't have multiple instances
Except
They do not get compiled at the same time
You can have different impls for debug and release for example
oh ok
still trying to get used to this typesystem
i have seen stuff like
Foldable<A, A=A> and that works for my HKT type that i found on some gist
and i am guessing that it says the inner type A should be equal to the outer type A
Assotiated type named
A is A
but its a bit foreign for me its the first typesystem i see that you have to do that
Yes
does anyone managed to debug tests in osx with vscode?
anybody use Helix? or develop for Helix?
Are there any major differences in using GDB vs LLDB?