handle recurrence

src/compiler/code.jl

@@ -6,7 +6,7 @@ export @model
 
 function process_func(ex, params = [])
   @capture(shortdef(ex), (args__,) -> body_)
-  body = Flow.il(graphm(body))
+  body = Flow.il(graphm(unblock(body)))
   body = mapconst(x -> x in params ? :(self.$x) : x, body)
   return args, body
 end
@@ -45,10 +45,12 @@ function deref_params(v)
 end
 
 function build_forward(body, args)
-  cse(deref_params(body))
+  iscyclic(body) && return :(error("Can't run forward pass on a cyclic graph"))
+  syntax(cse(deref_params(body)))
 end
 
 function build_backward(body, x, params = [])
+  iscyclic(body) && return :(error("Can't run backward pass on a cyclic graph"))
   Δs = invert(body)
   back = IVertex{Any}(Flow.Do())
   for param in params
@@ -60,7 +62,7 @@ function build_backward(body, x, params = [])
   ex = Δs[x]
   ex = deref_params(ex)
   thread!(back, @flow(tuple($ex)))
-  cse(back)
+  syntax(cse(back))
 end
 
 function process_type(ex)
@@ -73,8 +75,8 @@ function process_type(ex)
   @assert length(args) == 1
   quote
     $(build_type(T, params))
-    (self::$T)($(args...),) = $(syntax(build_forward(body, args)))
-    back!(self::$T, Δ, $(args...)) = $(syntax(build_backward(body, args[1], pnames)))
+    (self::$T)($(args...),) = $(build_forward(body, args))
+    back!(self::$T, Δ, $(args...)) = $(build_backward(body, args[1], pnames))
     update!(self::$T, η) = $(map(p -> :(update!(self.$p, η)), pnames)...)
     graph(::$T) = $(Flow.constructor(makegraph(body, args)))
     nothing
@@ -89,8 +91,8 @@ function process_anon(ex)
   end
   @assert length(args) == 1
   :(Flux.Capacitor(
-      ($(args...)) -> $(syntax(build_forward(body, args))),
-      (Δ, $(args...)) -> $(syntax(build_backward(body, args[1]))),
+      ($(args...)) -> $(build_forward(body, args)),
+      (Δ, $(args...)) -> $(build_backward(body, args[1])),
       η -> $(map(p -> :(update!($p, η)), layers)...),
       $(Flow.constructor(makegraph(body, args))))) |> esc
 end