feat: Experimental work on issue #50

i2/scrap/signature_bops.py

@@ -0,0 +1,46 @@
+"""Signature binary operators
+
+See design issue: https://github.com/i2mint/i2/issues/50
+"""
+
+from functools import partial
+
+from typing import Callable, TypeVar, Optional, Union
+
+B = TypeVar('B')
+B.__doc__ = (
+    "A 'base' type that we are able (example, builtin object) to operate on, as is"
+)
+A = TypeVar('A')
+A.__doc__ = "The 'abstract' type we want to operate on through a key-function"
+KeyFunction = Callable[[A], B]
+KeyFunction.__doc__ = 'Function that transforms an A to a B'
+
+AorB = TypeVar('AorB', A, B)
+AorB.__doc__ = 'An A (abstract) or a B (base)'
+AB = TypeVar('AB', bound=AorB)
+AorB.__doc__ = 'A generic AorB'
+R = TypeVar('R')
+R.__doc__ = 'The return type of a binary operator'
+
+BaseBinaryOperator = Callable[[B, B], R]
+AbstractBinaryOperator = Callable[[A, A], R]
+# BinaryOperator = Union[BaseBinaryOperator, AbstractBinaryOperator]  # equivalent?
+BinaryOperator = Callable[[AB, AB], R]
+KeyEnabledBinaryOperator = Callable[[AB, AB, KeyFunction], R]
+
+
+def key_function_enabled_operator(
+    binary_operator: Union[BaseBinaryOperator, AbstractBinaryOperator],
+    x: AB,
+    y: AB,  # has to be the same as x. If x is A, so should y, if x is B so should y
+    key: Optional[KeyFunction] = None,
+) -> R:
+    if key is None:
+        return binary_operator(x, y)
+    else:
+        return binary_operator(key(x), key(y))
+
+
+def key_function_factory(binary_operator: BinaryOperator) -> KeyEnabledBinaryOperator:
+    return partial(key_function_enabled_operator, binary_operator)