How to implement an iterator in Julia?

Question

I am trying to implement an iterator in Julia, but get an exception when the for-loop tries to call start already.

Here is what I get (I ran include(...), then using RDF):

julia> methods(start)
# 1 method for generic function "start":
start(graph::Graph) at /Users/jbaran/src/RDF.jl/src/RDF.jl:214

julia> for x in g
       println(x)
       end
ERROR: `start` has no method matching start(::Graph)
 in anonymous at no file

The function definition in the RDF module looks like this at the moment:

function start(graph::Graph)
    return GraphIterator(collect(keys(graph.statements)), nothing, nothing, nothing, [], [])
end

Any idea what I am doing wrong?

Answer 1

Don't forget to specify Base. - you are adding methods to an existing function.

module MyMod
  type Blah
    data
  end
  export Blah
  Base.start(b::Blah) = 1
  Base.done(b::Blah,state) = length(b.data) == state-1
  Base.next(b::Blah,state) = b.data[state], state+1
end
using MyMod
x = Blah([1,2,3])
for i in x
  println(i)
end

This works as of Julia 0.3.