Update recurrent.jl

Minor edits, adding some notes.

src/layers/recurrent.jl

@@ -99,13 +99,11 @@ function ChainRulesCore.rrule(
   # function is called in subsequent things...
   # hobbits = Vector{Tuple}(undef, length(x))  # Unfornately Zygote needs this
   # accum_init = ChainRulesCore.rrule_via_ad(config, op, init[1], nothing)
-  # @show typeof(accum_init)
   accum_init = ChainRulesCore.rrule_via_ad(config, op, init, x[1])
   hobbits = accumulate(x[begin+1:end]; init=accum_init) do (a, _), b
     @show a, b
     c, back = ChainRulesCore.rrule_via_ad(config, op, a, b)
   end
-  # @show typeof(hobbits)
 
   y = first(last(hobbits))
   axe = axes(x)
@@ -114,7 +112,6 @@ function ChainRulesCore.rrule(
     trio = accumulate(Iterators.reverse(hobbits); init=(0, dy, 0)) do (_, dc, _), (_, back)
       ds, da, db = back(dc)
     end
-    # @show trio
     f_ds, f_da, f_db = accum_init[2](trio[end][2])
     dop = sum(first, trio) + f_ds
     dx = [[f_db]; map(last, Iterators.reverse(trio))]
@@ -124,6 +121,7 @@ function ChainRulesCore.rrule(
   return y, unfoldl
 end
 
+# From Lux.jl
 # function ChainRulesCore.rrule(
 #   config::ChainRulesCore.RuleConfig{>:ChainRulesCore.HasReverseMode},
 #   ::typeof(Base.mapfoldl_impl),