You can obtain different types of iteration simply by wrapping "obj" in
different thin-wrappers. For example, you can define
immutable SomeOtherWayOfTraversing{T}
obj::T
end
which is used as
for x in SomeOtherWayOfTraversing(obj)
# blah
end
and then write the specific start, next, done methods like this:
start{T}(iter::SomeOtherWayOfTraversing{T})
You can get totally different behavior this way from what would happen when you
just say "for x in obj...".
You might want to browse through more packages to see more examples. Here's
one:
https://github.com/timholy/Grid.jl/blob/600cbcf645a73525fb6d563d5a148b9d8b2668aa/src/counter.jl
but many other packages (DataFrames, Gtk, HDF5, etc) define iterators.
--Tim
On Sunday, July 27, 2014 06:41:43 AM Ben Ward wrote:
> I'm not nessecerily trying it iterate over the children of a node. Rather I
> have defined a series of types that facilitate traversing a tree in various
> ways for my Phylogenetics.jl package, for example by depth first:
>
> type TraverserCore
> Start::PhyNode
> Behind::Stack
> History::Array{PhyNode, 1}
> Current::PhyNode
> end
>
>
> type DepthFirstTraverser <: TreeTraverser
> Ahead::Stack
> Core::TraverserCore
> function DepthFirstTraverser(tree::Phylogeny)
> x = new(Stack(PhyNode), TraverserCore(tree.Root, Stack(PhyNode), PhyNode
> [], tree.Root))
> for i in x.Core.Current.Children
> push!(x.Ahead, i)
> end
> return x
> end
> end
>
>
> It has methods like:
>
>
> function next!(x::DepthFirstTraverser)
> push!(x.Core.Behind, x.Core.Current)
> x.Core.Current = pop!(x.Ahead)
> for i in x.Core.Current.Children
> push!(x.Ahead, i)
> end
> end
>
>
> function getCurrent(x::TreeTraverser)
> return x.Core.Current
> end
>
>
> function hasReachedEnd(x::TreeTraverser)
> length(x.Ahead) > 0 ? false : true
> end
>
>
> Which seem similar to start, next, and done. I'd use them in a loop like so
> again from Phylogenetics.jl:
>
> while true
> show(getCurrent(traverser))
> if hasReachedEnd(traverser)
> break
> end
> next!(traverser)
> end
>
> But I'd like to make it behave more like an iterator - so be able to define
> the iterator methods for it so I can do something like
>
> for i = DepthFirstTraverser(myTree)
> # BLARGH
> end
>
> And it will be translated accordingly. I think this is doable by defining
> the three methods, making use of the types the method already has.
>
> The idea is to have a load of types that allow the user to code iteration
> over the tree in any possible way, easily, providing there is a
> TreeTraverser type for it.
>
> Best,
> Ben.
>
> On Sunday, July 27, 2014 2:14:38 PM UTC+1, Tim Holy wrote:
> > for x in obj
> >
> > # blah
> >
> > end
> >
> > will iterate if you've defined start, next, and done functions for which
> > the
> > first argument has typeof(obj). In your case you'd presumably use a node
> > as
> > obj, and the traversal would be recursively over all children of that
> > node.
> >
> > If you want a specific tree example, check out ProfileView.jl/src/tree.jl.
> >
> > Best,
> > --Tim
> >
> > On Sunday, July 27, 2014 05:13:39 AM Ben Ward wrote:
> > > Hi,
> > >
> > > I've been writing a type for recursive tree structures, and several
> >
> > types
> >
> > > that traverse that tree in various manners like breadth first or depth
> > > first. They have their own methods for getting the current tree node,
> > > moving to the next node, whether an end has been reached and so on. The
> > > contain fields for the nodes several steps ahead, those past etc. I
> > > wondered if I might make it so as these types might easier be used in
> >
> > loops
> >
> > > by giving them the iterator protocol methods? I've not seen how to
> >
> > define
> >
> > > custom operators, is it as simple as defining start next and done? How
> >
> > is
> >
> > > the current value gotten? I guess its returned by next().
> > >
> > > Thanks,
> > > Ben.
