tweak constants approach

src/backend/tensorflow/graph.jl

@@ -1,5 +1,6 @@
 using Base: @get!
-using DataFlow: Constant, constant, Context, interpret, Split
+using DataFlow: Constant, constant, Context, interpret, Split, interptuple, interplambda, interpconst
+using Flux: interpmap
 using TensorFlow: RawTensor
 
 # TODO: implement Julia's type promotion rules
@@ -36,8 +37,6 @@ graph(op::Op, xs...) = op.f(xs...)
 interp(ctx, c::Conv2D, x) =
   nn.conv2d(interpret(ctx, x), interp(ctx, Constant(c.filter)), [1,c.stride...,1], "VALID")
 
-interp(ctx, c::Constant) = node(c.value)
-
 interp{T<:AArray}(ctx, p::Constant{Flux.Param{T}}) =
   haskey(ctx[:params], p.value) ?
      ctx[:params][p.value] :
@@ -51,7 +50,7 @@ function interp(ctx, model, args...)
 end
 
 function tograph(model, args...)
-  ctx = Context(interp, params = ObjectIdDict())
+  ctx = Context(interplambda(interptuple(interpmap(interpconst(interp)))), params = ObjectIdDict())
   out = interp(ctx, model, map(constant, args)...)
   return ctx[:params], out
 end