Circuit ansatze should be dagger functors

lambeq/backend/grammar.py

@@ -362,6 +362,9 @@ def rotate(self, z: int) -> Diagrammable:
 
         """
 
+    def dagger(self) -> Diagrammable:
+        """Implements conjugation of diagrams."""
+
     def __matmul__(self, rhs: Diagrammable | Ty) -> Diagrammable:
         """Implements the tensor operator `@` with another diagram."""
 
@@ -1572,6 +1575,9 @@ def rotate(self, z: int) -> Self:
     def dagger(self) -> Box:
         return self.box
 
+    def apply_functor(self, functor: Functor) -> Diagrammable:
+        return functor(self.dagger()).dagger()
+
     @classmethod
     def from_json(cls, data: _JSONDictT | str) -> Self:
         data_dict = json.loads(data) if isinstance(data, str) else data

tests/backend/test_grammar.py

@@ -277,6 +277,7 @@ def ar(func, box):
     assert func(g.r) == func(g).r == g_z.r
     assert func(f >> g) == f_z >> g_z
     assert func(f @ g) == f_z @ g_z
+    assert func(f.dagger()) == func(f).dagger()
 
     def bad_ar(func, box):
         return Box("BOX", a, c) if box.cod == b else box

tests/test_circuit.py

@@ -320,3 +320,20 @@ def test_lambeq_tket_conversion():
 def test_special_characters(box, expected_sym_count):
     ansatz = Sim15Ansatz({n_ty: 2, comma_ty: 2, space_ty: 2}, n_layers=1)
     assert(len(ansatz(box).free_symbols) == expected_sym_count)
+
+
+def test_ansatz_is_dagger_functor():
+    ansatz = IQPAnsatz({N: 1, S: 1}, n_layers=1)
+    diagram = Word('John', N)
+    circuit1 = ansatz(diagram).dagger()
+    circuit2 = ansatz(diagram.dagger())
+    assert circuit1 == circuit2
+
+def test_ansatz_is_dagger_functor_sentence():
+    ansatz = IQPAnsatz({N: 1, S: 1}, n_layers=1)
+    diagram = (Word('Alice', N) @ Word('runs', N >> S) >>
+               Cup(N, N.r) @ S)
+
+    circuit1 = ansatz(diagram).dagger().normal_form()
+    circuit2 = ansatz(diagram.dagger()).normal_form()
+    assert circuit1 == circuit2