Why does Julia restrict dependent types to integers (or tuples thereof)?
julia> type Foo{a} end
julia> Foo{3}()
Foo{3}()
julia> Foo{"hello"}()
ERROR: type: apply_type: in Foo, expected Type{T<:Top}, got ASCIIString
julia> Foo{(1,2)}()
Foo{(1,2)}()
When I write code for rings over the integers, modulo N, I can stick N in
the type. It's great, because you don't want to mix your fields, so the
type keeps things separate, and you don't need extra storage space,
repeating N for each instance.
But when I want to do the equivalent for factor rings of polynomials (where
a polynomial is the equivalent of N above) then, suddenly, I cannot. I
cannot replace N above with a polynomial, because the type system won't
allow it (afaict). Yet the same arguments apply - I don't want to mix
factor rings (different polynomials give different types) and I don't want
to repeat the factor in each instance - it's just wasting storage space.
What is the reason for this (apparently arbitrary) restriction? I think I
can work round it by encoding the polynomial as a tuple of integers, but
it's going to be painful, and likely inefficient.
And sorry I am asking multiple questions today. I feel like I am sitting
here complaining about everything just because I am ignorant...
Andrew
PS How does the logic of the error above work? How are integers types? Is
it special cased in the compiler?
