Scalding viz options

[MansurAshraf]

Continuation of #1426 with published Chill version

[rubanm]

Should this be a Semigroup? Looks like a side-effecting function here. Are we guaranteed associativity?

[MansurAshraf]

I think strategies will be applied in a sequence so it is associative (and not commutative)? /cc @ianoc as he wrote this.

[Gabriella439]

Yep, this is a semigroup because plus is assocative

[johnynek]

It's not side-effecting. Nothing happens in plus. It is just creating a new strategy. Looks correct to me.

[Gabriella439]

Making an analogy to Haskell, it's equivalent to the semigroup over this type:

newtype FlowStepStrategy a =
    FlowStepStrategy (Flow a -> JList (FlowStep a) -> FlowStep a -> IO ())

instance Monoid (FlowStepStrategy a) where
    mempty = FlowStepStrategy (\_ _ _ -> return ())

    mappend (FlowStepStrategy f1) (FlowStepStrategy f2) = FlowStepStrategy f
      where
        f x y z = do
            f1 x y z
            f2 x y z

... and that's guaranteed to satisfy the Monoid laws in both Haskell and Scala.

The most common source of this thing failing in Scala specifically is if side effects are triggered prematurely by evaluating things in the wrong order but that does not appear to be the case for this code.

[rubanm]

Ah ok. What I was confused about was if plus(a, plus(b, c)).apply and plus(plus(a, b), c).apply will have the same effect.

[johnynek]

why didn't you use the case style here?

[johnynek]

also, use caused-by constructor (see below).

[johnynek]

Lgtm. What's up with the version number? What does exec mean here?

[rubanm]

+1

[coveralls]

Changes Unknown when pulling 899b645 on MansurAshraf:mashraf/scalding_viz into ** on twitter:develop**.