Atom can't evaluate a line which the regular REPL can

juno
knet

#1

Hello,

I encountered this error when using a registered Julia package called “Knet” yet I wasn’t sure whether to post it as an issue for Knet or ask it here. I eventually decided to ask about it here as the error was only reproducible in Atom but the code ran smoothly in the regular Julia REPL.

So here is the problem:

I am using a deep learning package called Knet. When I run the following code at the REPL I get the desired results and expected outputs:

julia> using Knet

julia> x = Param([1,2,3])
3-element Param{Array{Int64,1}}:
 1
 2
 3

julia> y = @diff sum(abs2,x)
T(14)

julia> println(grad(y, x))
[2, 4, 6]

Param, @diff and grad are Knet functions. The documentation regarding them are as follows:

   Param(x) returns a struct that acts like x but marks it as a parameter you want to compute
   gradients with respect to.
 
   @diff expr evaluates an expression and returns a struct that contains its value (which should be
   a scalar) and gradient information.
 
   grad(y, x) returns the gradient of y (output by @diff) with respect to any parameter x::Param,
   or nothing if the gradient is 0.

Yet when I try to run the same code line by line using Shift+Enter in Atom first two line run with no problem and the third line (namely y = @diff sum(abs2,x)) produces the following error:

Julia Client – Internal Error
MethodError: no method matching iterate(::AutoGrad.Node)
Closest candidates are:
  iterate(!Matched::Core.SimpleVector) at essentials.jl:578
  iterate(!Matched::Core.SimpleVector, !Matched::Any) at essentials.jl:578
  iterate(!Matched::ExponentialBackOff) at error.jl:171

What seems to be the problem here?


#2

I would argue that this is a “bug” in AutoGrad.jl, because they introduce a typealias for Tape = IdDict{Value,Node} and overload iterate for that to return something different from a normal AbstractDict. Usually one would expect to get a key => value pair back, but iterate(::Tape, ...) only returns the value.

On the Juno side, the issue only appears since


was merged, because before that PR we would’ve just used the (working) show method for the Tape.