initial work on loops

src/Flux.jl

@@ -14,6 +14,7 @@ back!(m::Model, ∇) = error("Backprop not implemented for $(typeof(m))")
 update!(m::Model, η) = m
 
 include("compiler/diff.jl")
+include("compiler/loop.jl")
 include("compiler/code.jl")
 
 include("cost.jl")

src/compiler/code.jl

@@ -27,6 +27,7 @@ function build_type(T, params, temps)
 end
 
 function build_forward(body, temps)
+  body = cut_forward(body)
   forward = IVertex{Any}(Flow.Do())
   for (ex, k) in temps
     k = Expr(:quote, k)
@@ -75,8 +76,19 @@ function process_type(ex)
   end |> longdef |> MacroTools.flatten
 end
 
-process_type(:(type Sigmoid
-  W
-  b
-  x -> σ(W*x+b)
+# process_type(:(type Sigmoid
+#   W
+#   b
+#   bp
+#   x -> σ(W*x+b)
+# end)) |> prettify
+
+process_type(:(type Recurrent
+  Wxh; Whh; Bh
+  Why; By
+
+  function (x)
+    hidden = σ( Wxh*x + Whh*Delay(hidden) + Bh )
+    y = σ( Why*hidden + By )
+  end
 end)) |> prettify

src/compiler/loop.jl

@@ -0,0 +1,16 @@
+function cut_forward(v::IVertex)
+  pushes = []
+  Flow.prefor(v) do w
+    value(w) == :Delay &&
+      push!(pushes, vertex(:push!, vertex(:(self.delay)), w[1]))
+  end
+  isempty(pushes) && return v
+  @assert length(pushes) == 1
+  v = vertex(Flow.Do(), pushes..., v)
+  prewalk(v) do v
+    value(v) == :Delay || return v
+    il(@flow(pop!(self.delay)))
+  end
+end
+
+cut_forward(g)