Change Normal{P,X} to Normal{X,P}

[cscherrer]

@phipsgabler suggested this, so users can write, e.g.,

Normal{Float64}

instead of

Normal{P,Float64} where {P}

Any objections @mschauer @simeonschaub @femtomc ?

[cscherrer]

To be clear, this is just an example - we need a general pattern for measures that can follow different parameterizations.

One possible counterargument: The current setup makes it a bit easier to talk about generic measure types on X, since we can have e.g.

M{Float64}

and M might be Lebesgue or Normal{P} for some P.

Starting this issue I was "all in", but now I'm back to undecided. What do you think?

[mschauer]

in favor, there might be no P at all.

[cscherrer]

in favor, there might be no P at all.

Good point. And e.g. Array{T,N} is a a generalization of Vector{T}, also an argument toward "put X first". Are there standard Julia examples that go the other way? If not I'd say the change is the way to go.

[cscherrer]

Since X can be determined statically from P, we might not need X to be in the type anyway. Let's try it out this way and see how it goes - we can come back to this if we need to. I'll close this now.