Raise an exception when applying ansatze on a diagram with frames (#222)

* Added new `SplitTensorAnsatz` for tensor network ansatzes that splits large boxes into smaller units
* Reorganize tests and imports

lambeq/ansatz/base.py

@@ -20,13 +20,21 @@
 """
 from __future__ import annotations
 
-__all__ = ['BaseAnsatz', 'Symbol']
+__all__ = ['BaseAnsatz']
 
 from abc import ABC, abstractmethod
 from collections.abc import Mapping
 
 from lambeq.backend import grammar, tensor
-from lambeq.backend.symbol import Symbol
+
+
+AnsatzWithFramesRuntimeError = RuntimeError(
+    'Attempting to apply an ansatz to a diagram '
+    'with frames. Try using `sandwich=True` when '
+    'calling `DisCoCircReader.text2circuit()` '
+    'or applying a custom functor that converts '
+    'frames to boxes before applying an ansatz.'
+)
 
 
 class BaseAnsatz(ABC):

lambeq/ansatz/circuit.py

@@ -36,7 +36,7 @@
 
 import numpy as np
 
-from lambeq.ansatz import BaseAnsatz
+from lambeq.ansatz.base import AnsatzWithFramesRuntimeError, BaseAnsatz
 from lambeq.backend.grammar import Box, Diagram, Functor, Ty
 from lambeq.backend.quantum import (
     Bra,
@@ -111,6 +111,10 @@ def __init__(self,
 
     def __call__(self, diagram: Diagram) -> Circuit:
         """Convert a lambeq diagram into a lambeq circuit."""
+
+        if diagram.has_frames:
+            raise AnsatzWithFramesRuntimeError
+
         return self.functor(diagram)  # type: ignore[return-value]
 
     def ob_size(self, pg_type: Ty) -> int:

lambeq/ansatz/tensor.py

@@ -22,9 +22,10 @@
 
 __all__ = ['TensorAnsatz', 'MPSAnsatz', 'SpiderAnsatz']
 
+from abc import abstractmethod
 from collections.abc import Mapping
 
-from lambeq.ansatz import BaseAnsatz
+from lambeq.ansatz.base import AnsatzWithFramesRuntimeError, BaseAnsatz
 from lambeq.backend import grammar, Symbol, tensor
 from lambeq.backend.grammar import Cup, Spider, Ty, Word
 from lambeq.backend.tensor import Dim
@@ -108,10 +109,33 @@ def _generate_directed_dom_cod(self, box: grammar.Box) -> tuple[Dim, Dim]:
 
     def __call__(self, diagram: grammar.Diagram) -> tensor.Diagram:
         """Convert a diagram into a tensor."""
+
+        if diagram.has_frames:
+            raise AnsatzWithFramesRuntimeError
+
         return self.functor(diagram)  # type: ignore[return-value]
 
 
-class MPSAnsatz(TensorAnsatz):
+class SplitTensorAnsatz(TensorAnsatz):
+    """Base class for tensor network ansatzes that splits large boxes
+    into smaller units."""
+
+    split_functor: grammar.Functor
+
+    @abstractmethod
+    def _split_ar(self, _: grammar.Functor, ar: Word) -> grammar.Diagrammable:
+        """Split large boxes into smaller units."""
+
+    def __call__(self, diagram: grammar.Diagram) -> tensor.Diagram:
+        if diagram.has_frames:
+            raise AnsatzWithFramesRuntimeError
+
+        return self.functor(
+            self.split_functor(diagram)
+        )  # type: ignore[return-value]
+
+
+class MPSAnsatz(SplitTensorAnsatz):
     """Split large boxes into matrix product states."""
 
     BOND_TYPE: Ty = Ty('B')
@@ -169,13 +193,8 @@ def _split_ar(self, _: grammar.Functor, ar: Word) -> grammar.Diagrammable:
         return (grammar.Id().tensor(*boxes)
                 >> grammar.Id().tensor(*cups[:-1]))  # type: ignore[arg-type]
 
-    def __call__(self, diagram: grammar.Diagram) -> tensor.Diagram:
-        return self.functor(
-            self.split_functor(diagram)
-        )  # type: ignore[return-value]
-
 
-class SpiderAnsatz(TensorAnsatz):
+class SpiderAnsatz(SplitTensorAnsatz):
     """Split large boxes into spiders."""
 
     def __init__(self,
@@ -220,8 +239,3 @@ def _split_ar(self, _: grammar.Functor, ar: Word) -> grammar.Diagrammable:
 
         return (grammar.Id().tensor(*boxes)
                 >> grammar.Id().tensor(*spiders))
-
-    def __call__(self, diagram: grammar.Diagram) -> tensor.Diagram:
-        return self.functor(
-            self.split_functor(diagram)
-        )  # type: ignore[return-value]

lambeq/backend/pennylane.py

@@ -430,7 +430,7 @@ def param_substitution(self, weights):
             The weights to substitute for the symbols.
 
         Returns
-        -------e
+        -------
         :class:`torch.FloatTensor`
             The concrete (non-symbolic) parameters for the
             circuit.

lambeq/training/model.py

@@ -26,7 +26,7 @@
 
 from sympy import Symbol as SymPySymbol
 
-from lambeq.ansatz.base import Symbol
+from lambeq.backend.symbol import Symbol
 from lambeq.backend.tensor import Diagram
 from lambeq.training.checkpoint import Checkpoint
 from lambeq.typing import StrPathT

lambeq/training/pytorch_model.py

@@ -25,8 +25,8 @@
 
 import torch
 
-from lambeq.ansatz.base import Symbol
 from lambeq.backend.numerical_backend import backend
+from lambeq.backend.symbol import Symbol
 from lambeq.backend.tensor import Diagram
 from lambeq.training.checkpoint import Checkpoint
 from lambeq.training.model import Model

lambeq/training/pytorch_quantum_model.py

@@ -23,9 +23,9 @@
 
 import torch
 
-from lambeq.ansatz.base import Symbol
 from lambeq.backend.numerical_backend import backend
 from lambeq.backend.quantum import Diagram as Circuit
+from lambeq.backend.symbol import Symbol
 from lambeq.backend.tensor import Diagram
 from lambeq.training.checkpoint import Checkpoint
 from lambeq.training.quantum_model import QuantumModel