Given

Int i = ...
Num num = ...

Why does the following compile:

echo(i * num)

while the following does not:

echo(num * i)

I understand the class rationale, but the lack of symmetry over mult is confusing as an end result.

I agree it isn't ideal, but is really because of two independent features interacting together:

i*num  => i.mult(num) =>  i.mult((Int)num)

So the * shortcut turns into the normal mult method. Then the auto-cast feature doesn't force you to insert the manual Int cast.

So there is really only Int.mult(Int). Num doesn't have a mult method, since we'd have to support contra-variance to efficiently limit Int.mult to only take an Int.

Fan doesn't have the numerical tower like scheme languages.

Just to add that not all number systems are commutative and associative for addition and multiplication ;-)