csys: provide compose() function for combining synapse operators

lib/csys/csys.ex

@@ -78,4 +78,19 @@ defmodule Scopes.CSys do
   def proc(scope), do: elem(scope, 1)
   def syns(scope), do: elem(scope, 2)
   def env(scope), do: elem(scope, 3)
+
+  # helpers
+
+  def compose(ops) do
+    fn msg ->
+      Enum.reduce(ops, msg, 
+        fn op, val ->
+          case val do
+            nil -> nil
+            val -> op.(val)
+          end
+        end
+      )
+    end
+  end
 end

test/csys_test.exs

@@ -29,17 +29,17 @@ defmodule Scopes.CSysTest do
       #CSys.send_message(zero, [:csys, :create, :pred], %{op: neg_only()})
       CSys.send_message(zero, [:csys, :create, :pred], %{op: Program.negate()})
       one = receive_data([:csys, :created]).new
-      CSys.send_message(one, [:csys, :create, :succ], %{op: CSys.data_only()})
+      CSys.send_message(one, [:csys, :create, :succ], 
+        %{op: CSys.compose([CSys.data_only(), Program.negate()])})
       two = receive_data([:csys, :created]).new
       Process.sleep(1)
       CSys.send_value(one, 1)
-      #assert 1 = receive_data().value
-      assert Enum.member?([-1, 1], receive_data().value)
-      assert Enum.member?([-1, 1], receive_data().value)
+      assert receive_data().value in [-1, 1]
+      assert receive_data().value in [-1, 1]
       CSys.send_message(two, [:csys, :create, :pred])
       three = receive_data([:csys, :created]).new
       CSys.send_message(three, [:csys, :connect], %{target: zero})
-      Process.sleep(1)
+      Process.sleep(2)
       CSys.send_value(three, 3)
       assert 3 = receive_data().value
       assert 3 = receive_data().value