On Thu, Jul 2, 2015 at 10:48 AM, Tom Breloff <[email protected]> wrote:
> Just curious... is there a reason simply checking for non-zero isn't enough?
> Readability? Performance?
>
> f(a,b,c) = (Bool(a) ? a * (b + c) : 0.0)
I'm guessing he want all code that gets his type automatically gets
this behavior? If yes, I don't think there's anyway you can do that.
If not, then just writing the branch or having a macro to rewrite that
in your own code is probably the best solution.
>
>
>
> On Thursday, July 2, 2015 at 9:47:59 AM UTC-4, Jan Drugowitsch wrote:
>>
>> Dear Julia users,
>>
>> I am implementing an algorithm to solve a specific type of Volterra
>> integral equation, and that simplifies significantly if some of its
>> parameters are set to zero or one. The function implementing the algorithm
>> takes quite a few arguments, such that writing specific versions for
>> different arguments being zero/one would lead to too many different
>> functions, which I would like to avoid. What I would rather like to do is to
>> write one generic function and let the compiler prune different parts of the
>> function, depending on the argument types.
>>
>> A minimal example of what I would like to do is
>>
>> immutable Zero <: Number; end
>>
>> const _zero = Zero()
>>
>> Base.promote_rule{T<:Number}(::Type{Zero}, ::Type{T}) = T
>> Base.convert{T<:Number}(::Type{T}, ::Zero) = zero(T)
>>
>> *(::Zero, ::Zero) = _zero
>> *(::Zero, ::Bool) = _zero
>> *(::Bool, ::Zero) = _zero
>> *(::Zero, ::Number) = _zero
>> *(::Number, ::Zero) = _zero
>>
>> f(a, b, c) = a * (println("summing b + c"); b + c)
>>
>> println("Evaluating f(0, 1, 2)")
>> f(0, 1, 2)
>> println("Evaluating f(_zero, 1, 2)")
>> f(_zero, 1, 2)
>>
>> (with Zero defined similar to
>> https://groups.google.com/forum/#!topic/julia-users/0ab30bE8q6c)
>> Running the above results in
>>
>> Evaluating f(0, 1, 2)
>> summing b + c
>> Evaluating f(_zero, 1, 2)
>> summing b + c
>>
>> even though the result of the second "summing b + c" is discarded, and
>> therefore wouldn't need to be evaluated. This is no surprise, as *(.,.) is a
>> standard function that evaluates its operands before applying the function.
>> Is there any way to change this behavior and turn *(.,.) into a function
>> that performs short-circuit evaluation? If not, is there an alternative
>> approach that achieves this without writing tons of specialized functions?
>>
>> Thanks,
>> Jan
