preserve default values for hidden states

src/compiler/code.jl

@@ -14,7 +14,9 @@ end
 function makegraph(graph, args)
   @assert length(args) == 1
   mapconst(graph) do x
-    x == args[1] ? ModelInput(1) : x
+    x == args[1] ? ModelInput(1) :
+    isa(x, Delay) ? :(Delay($(Expr(:quote, x.name)), self.$(x.name))) :
+    x
   end
 end
 

src/compiler/loops.jl

@@ -1,7 +1,10 @@
 type Delay
   name::Symbol
+  default::Nullable{Param}
 end
 
+Delay(name) = Delay(name, nothing)
+
 function liftloops!(ex, params)
   e = Flow.normedges(ex)
   hidden = intersect((b.args[1] for b in ex.args), params)
@@ -42,13 +45,15 @@ end
 function break!(g::IVertex)
   g = bumpinputs(g)
   loops = []
+  defaults = []
   g = prewalk!(g) do v
     isa(value(v), Delay) || return v
     n = length(loops)+1
     push!(loops, unroll!(v, n))
+    push!(defaults, get(value(v).default))
     hinput(n)
   end
-  cse(vertex(tuple, vertex(tuple, loops...), g))
+  cse(vertex(tuple, vertex(tuple, loops...), g)), defaults
 end
 
 # r = Recurrent(10, 10)