From e53ce879001be51f6fda9a39a588ec7132a790a3 Mon Sep 17 00:00:00 2001
From: Helmut Merz <helmutm@cy55.de>
Date: Fri, 15 May 2026 17:03:05 +0200
Subject: [PATCH] csys: more on synapse operations: filter_head, data_only

---
 lib/csys/csys.ex   | 9 +++++++++
 test/csys_test.exs | 9 ++-------
 2 files changed, 11 insertions(+), 7 deletions(-)

diff --git a/lib/csys/csys.ex b/lib/csys/csys.ex
index 8e3b9e2..b302acc 100644
--- a/lib/csys/csys.ex
+++ b/lib/csys/csys.ex
@@ -35,6 +35,15 @@ defmodule Scopes.CSys do
   
   def noop(msg), do: msg
 
+  def filter_head(pat) do
+    fn msg -> 
+      head = Shape.head(msg)
+      if List.starts_with?(head, pat), do: msg
+    end
+  end
+
+  def data_only(), do: filter_head([:csys, :data])
+
   # `send` shortcuts
 
   def send_message(rcvr, head, data \\ %{}) do
diff --git a/test/csys_test.exs b/test/csys_test.exs
index 8f33a55..e52d82d 100644
--- a/test/csys_test.exs
+++ b/test/csys_test.exs
@@ -17,10 +17,7 @@ defmodule Scopes.CSysTest do
   end
 
   def neg_only(msg) do
-    val = Shape.data(msg)[:value]
-    if val && val < 0 do
-      msg
-    end
+    if Shape.data(msg)[:value] < 0, do: msg
   end
 
   describe "basic:" do
@@ -28,16 +25,14 @@ defmodule Scopes.CSysTest do
       zero = Environ.setup(Program.prepare_basic())
       CSys.send_value(zero, "Hello Zero!")
       assert "Hello Zero!" = receive_data().value
-      #CSys.send_message(zero, [:csys, :create, :pred])
       CSys.send_message(zero, [:csys, :create, :pred], %{op: &neg_only/1})
       assert_receive {:created, new1}
-      CSys.send_message(new1, [:csys, :create, :succ])
+      CSys.send_message(new1, [:csys, :create, :succ], %{op: CSys.data_only()})
       assert_receive {:created, _new2}
       CSys.send_value(new1, "Hello New1!")
       assert "Hello New1!" = receive_data().value
       #assert "Hello New1!" = receive_data().value
       Process.sleep(50)
-      # Actor.stop(zero)
       refute_received msg, "unhandled message(s): #{inspect(msg)}"
     end
   end