remove MultisetEvaluator.validate_arity() since the number of argum…

…ents to `next_state()` usually works well enough

courtesy check in `output_arity()` that each input has `output_arity` exactly 1

src/icepool/__init__.py

@@ -126,7 +126,12 @@
 from icepool.generator.compound_keep import CompoundKeepGenerator
 from icepool.generator.mixture import MixtureGenerator
 
-from icepool.multiset_expression import MultisetExpression, implicit_convert_to_expression, InitialMultisetGeneration, PopMultisetGeneration, MultisetBindingError
+from icepool.multiset_expression import (MultisetExpression,
+                                         implicit_convert_to_expression,
+                                         InitialMultisetGeneration,
+                                         PopMultisetGeneration,
+                                         MultisetArityError,
+                                         MultisetBindingError)
 
 from icepool.generator.multiset_generator import MultisetGenerator
 from icepool.generator.alignment import Alignment

src/icepool/evaluator/argsort.py

@@ -1,6 +1,7 @@
 __docformat__ = 'google'
 
 from icepool.evaluator.multiset_evaluator import MultisetEvaluator
+from icepool.multiset_expression import MultisetArityError
 
 from icepool.order import Order, OrderReason
 from typing import Any

src/icepool/evaluator/basic.py

@@ -4,6 +4,7 @@
 
 import icepool
 from icepool.evaluator.multiset_evaluator import MultisetEvaluator
+from icepool.multiset_expression import MultisetArityError
 from icepool.order import Order, OrderReason
 
 import operator

src/icepool/evaluator/joint.py

@@ -96,10 +96,6 @@ def _bound_inputs(self) -> 'tuple[icepool.MultisetExpression, ...]':
     def bound_inputs(self) -> 'tuple[icepool.MultisetExpression, ...]':
         return self._bound_inputs
 
-    def validate_arity(self, arity: int) -> None:
-        for subeval in self._sub_evaluators:
-            subeval.validate_arity(arity)
-
     @cached_property
     def _extra_arity(self) -> int:
         return sum(expression.output_arity()

src/icepool/evaluator/multiset_evaluator.py

@@ -179,19 +179,6 @@ def bound_inputs(self) -> 'tuple[icepool.MultisetExpression, ...]':
         """
         return ()
 
-    def validate_arity(self, arity: int) -> None:
-        """An optional method to verify the total input arity.
-
-        This is called after any implicit conversion to expressions, but does
-        not include any `bound_inputs()`.
-
-        Overriding `next_state` with a fixed number of counts will make this
-        check redundant.
-
-        Raises:
-            `ValueError` if the total input arity is not valid.
-        """
-
     @cached_property
     def _cache(
         self
@@ -254,11 +241,11 @@ def evaluate(
             from icepool.evaluator.multiset_function import MultisetFunctionEvaluator
             return MultisetFunctionEvaluator(*inputs, evaluator=self)
 
-        self.validate_arity(
-            sum(expression.output_arity() for expression in inputs))
-
         inputs = self.bound_inputs() + inputs
 
+        # This is kept to verify inputs to operators each have arity exactly 1.
+        total_arity = sum(input.output_arity() for input in inputs)
+
         if not all(expression._is_resolvable() for expression in inputs):
             return icepool.Die([])
 

src/icepool/generator/mixture.py

@@ -2,7 +2,7 @@
 
 import icepool
 
-from icepool.multiset_expression import InitialMultisetGeneration, PopMultisetGeneration
+from icepool.multiset_expression import MultisetArityError, InitialMultisetGeneration, PopMultisetGeneration
 from icepool.generator.multiset_generator import MultisetGenerator
 from icepool.order import Order, OrderReason, merge_order_preferences
 
@@ -72,7 +72,7 @@ def output_arity(self) -> int:
             if result is None:
                 result = inner.output_arity()
             elif result != inner.output_arity():
-                raise ValueError('Inconsistent output_arity.')
+                raise MultisetArityError('Inconsistent output_arity.')
         if result is None:
             raise ValueError('Empty MixtureMultisetGenerator.')
         return result

src/icepool/multiset_expression.py

@@ -24,6 +24,10 @@
                                                   Sequence, int]]
 
 
+class MultisetArityError(ValueError):
+    """Indicates that an arity was not the same as required."""
+
+
 class MultisetBindingError(TypeError):
     """Indicates a bound multiset variable was found where a free variable was expected, or vice versa."""
 

src/icepool/operator/multiset_operator.py

@@ -1,7 +1,7 @@
 __docformat__ = 'google'
 
 import icepool
-from icepool.multiset_expression import MultisetExpression, InitialMultisetGeneration, PopMultisetGeneration
+from icepool.multiset_expression import MultisetExpression, InitialMultisetGeneration, PopMultisetGeneration, MultisetArityError
 
 import itertools
 import math
@@ -51,7 +51,15 @@ def outcomes(self) -> Sequence[T]:
                                       for child in self._children))
 
     def output_arity(self) -> int:
-        """Transforms only output 1 count. For multiple outputs, use @multiset_function."""
+        """Operators only output 1 count.
+
+        Each input to `MultisetOperator` must only output 1 count as well.
+
+        For multiple outputs, use @multiset_function.
+        """
+        if any(child.output_arity() != 1 for child in self._children):
+            raise MultisetArityError(
+                'Each input to MultisetOperator must output exactly 1 count.')
         return 1
 
     def _is_resolvable(self) -> bool:

tests/deck_test.py

@@ -3,6 +3,7 @@
 
 from icepool import MultisetEvaluator, Deck
 from icepool.evaluator import LargestStraightEvaluator
+from icepool.multiset_expression import MultisetArityError
 
 # no wraparound
 best_run_evaluator = LargestStraightEvaluator()
@@ -62,8 +63,8 @@ def test_two_hand_sum_diff_size():
 def test_multiple_bind_error():
     deck = icepool.Deck(range(4), times=4)
     deal = deck.deal(2, 2)
-    with pytest.raises(ValueError):
-        deal.unique()
+    with pytest.raises(MultisetArityError):
+        deal.unique().count()
 
 
 def test_add():