Why can't you keep track of everything in the state variable, and make your
iterator-types trivial?
--Tim
On Sunday, July 27, 2014 11:07:36 AM Ben Ward wrote:
> My traverser types are not exactly wrappers quite a simple as they contain
> FIFO and FILO structures that keep track of things - I struggle to imagine
> how else to have them. Do the three iterate methods necessarily need to
> have the second argument "state"? My types know they are done -
> hasReachedEnd() - because there are no more nodes to visit in their Ahead
> Queue/Stack. So would a done() that only requires the type be sufficient
> with no state input variable as in done(tier, state)?
>
> Best,
> Ben.
>
> On Sunday, July 27, 2014 4:49:24 PM UTC+1, Tim Holy wrote:
> > 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/600cbcf645a73525fb6d563d5a148b9d8b
> > 2668aa/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.
