diff --git a/scopes/core/core.py b/scopes/core/core.py
index 027491b..dd0bf96 100644
--- a/scopes/core/core.py
+++ b/scopes/core/core.py
@@ -18,6 +18,7 @@ type Categ = tuple[Symbol, Symbol]
 type Proc = Callable[[Message, Scope], Awaitable[Scope | None]]
 type Program = Callable[[Scope], Proc]
 type Syn = Callable[[Message], Message]
+type ProgramSpec = dict[tuple[Symbol, Symbol], Proc]
 
 type Handler = Callable[[Message, Scope], 
      Awaitable[Message | None | tuple[Message | None, Scope | None]]]
@@ -29,6 +30,15 @@ async def proc_dummy(msg: Message, scope: Scope) -> None:
 
 global_mailbox: Mailbox = asyncio.Queue()
 
+def gen_program(spec: ProgramSpec, default: Proc = proc_dummy) -> Program:
+    def program(scope: Scope) -> Proc:
+        key = (scope.categ[1], scope.stage)
+        proc = spec.get(key, spec.get((key[0], k.default)))
+        if proc is None:
+            proc = spec.get((k.default, key[1]), default)
+        return proc
+    return program
+
 @dataclass
 class Scope:
 
@@ -36,7 +46,7 @@ class Scope:
     categ: Categ = (k.csys, k.c00)
     stage: Symbol = k.initial
     proc: Proc = field(init=False)
-    program: Program = lambda x: proc_dummy
+    program: Program = gen_program({})
     syns: list[Syn] = field(default_factory=list)
     environ: Mailbox = global_mailbox