[julia-users] Help understanding types parameterized by constants

[Glen Hertz]

Hi,

Perhaps I'm doing this the wrong way but I wanted to parameterize some 
types by a constant, Year, like so:

abstract TaxForm{Year}


type Form1{2013} <: TaxForm{2013}
    a
    b
    c
    Form1{2013}() = new(0.0, 0.0, 0.0)
end


type Form1{2012} <: TaxForm{2012}
    a
    b
    # no C field
    Form1{2013}() = new(0.0, 0.0, 0.0)
end


type Form2{2013} <: TaxForm{2013}
    e
    f
    g
    Form2{2013}() = new(0.0, 0.0, 0.0)
end


type Form2{2012} <: TaxForm{2012}
    e2 # different fields this year
    f2
    g2
    Form2{2012}() = new(0.0, 0.0, 0.0)
end


# Create all tax form for a given year:
createforms(Year::Int) = {Form1{Year}(), Form2{Year}()}

tax_payable(f::Form1{2013}) = max(2*f.a, 0.0) + max(f.b, 0.0) + max(0.95*f.c
, 0.0)
tax_payable(f::Form1{2012}) = max(3*f.a, 0.0) + max(f.b, 0.0)

tax_payable(f::Form2{2013}) = max(f.e, 0.0) + max(f.f, 0.0) + max(0.91*f.g, 
0.0)
tax_payable(f::Form2{2012}) = max(e2.a, 0.0) + max(f.f2, 0.0) + max(0.93*f.
g2, 0.0)

The fields of the form are different from form to form, and the same form 
can change year to year.  I've tried quite a few combinations and I get 
syntax errors.

Any recommendations how to code something like this?

Yes, it is Tax time....

Glen