From 3f28929d0743bb510590e7cc53b0d05457d20bd6 Mon Sep 17 00:00:00 2001
From: Michael Whittaker <mjwhittaker@berkeley.edu>
Date: Wed, 20 Jan 2021 16:12:26 -0800
Subject: [PATCH] Added basic library skeleton.

---
 quorums/quorums.py | 127 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 127 insertions(+)
 create mode 100644 quorums/quorums.py

diff --git a/quorums/quorums.py b/quorums/quorums.py
new file mode 100644
index 0000000..88bb47d
--- /dev/null
+++ b/quorums/quorums.py
@@ -0,0 +1,127 @@
+from typing import Iterator, Generic, List, Set, TypeVar
+import itertools
+
+
+T = TypeVar('T')
+
+
+class Expr(Generic[T]):
+    def quorums(self) -> Iterator[Set[T]]:
+        raise NotImplementedError
+
+    def is_quorum(self, xs: Set[T]) -> bool:
+        raise NotImplementedError
+
+    def dual(self) -> 'Expr[T]':
+        raise NotImplementedError
+
+    def __add__(self, rhs: 'Expr[T]') -> 'Expr[T]':
+        return _or(self, rhs)
+
+    def __mul__(self, rhs: 'Expr[T]') -> 'Expr[T]':
+        return _and(self, rhs)
+
+
+def _and(lhs: Expr[T], rhs: Expr[T]) -> Expr[T]:
+    if isinstance(lhs, And) and isinstance(rhs, And):
+        return And(lhs.es + rhs.es)
+    elif isinstance(lhs, And):
+        return And(lhs.es + [rhs])
+    elif isinstance(rhs, And):
+        return And([lhs] + rhs.es)
+    else:
+        return And([lhs, rhs])
+
+
+def _or(lhs: Expr[T], rhs: Expr[T]) -> Expr[T]:
+    if isinstance(lhs, Or) and isinstance(rhs, Or):
+        return Or(lhs.es + rhs.es)
+    elif isinstance(lhs, Or):
+        return Or(lhs.es + [rhs])
+    elif isinstance(rhs, Or):
+        return Or([lhs] + rhs.es)
+    else:
+        return Or([lhs, rhs])
+
+
+class Node(Expr[T]):
+    def __init__(self, x: T) -> None:
+        self.x = x
+
+    def __str__(self) -> str:
+        return str(self.x)
+
+    def __repr__(self) -> str:
+        return f'Node({self.x})'
+
+    def quorums(self) -> Iterator[Set[T]]:
+        yield {self.x}
+
+    def is_quorum(self, xs: Set[T]) -> bool:
+        return self.x in xs
+
+    def dual(self) -> Expr:
+        return self
+
+
+class Or(Expr[T]):
+    def __init__(self, es: List[Expr[T]]) -> None:
+        if len(es) == 0:
+            raise ValueError(f'Or cannot be constructed with an empty list')
+
+        self.es = es
+
+    def __str__(self) -> str:
+        return '(' + ' + '.join(str(e) for e in self.es) + ')'
+
+    def __repr__(self) -> str:
+        return f'Or({self.es})'
+
+    def quorums(self) -> Iterator[Set[T]]:
+        for e in self.es:
+            yield from e.quorums()
+
+    def is_quorum(self, xs: Set[T]) -> bool:
+        return any(e.is_quorum(xs) for e in self.es)
+
+    def dual(self) -> Expr:
+        return And([e.dual() for e in self.es])
+
+
+class And(Expr[T]):
+    def __init__(self, es: List[Expr[T]]) -> None:
+        if len(es) == 0:
+            raise ValueError(f'And cannot be constructed with an empty list')
+
+        self.es = es
+
+    def __str__(self) -> str:
+        return '(' + ' * '.join(str(e) for e in self.es) + ')'
+
+    def __repr__(self) -> str:
+        return f'And({self.es})'
+
+    def quorums(self) -> Iterator[Set[T]]:
+        for subquorums in itertools.product(*[e.quorums() for e in self.es]):
+            yield set.union(*subquorums)
+
+    def is_quorum(self, xs: Set[T]) -> bool:
+        return all(e.is_quorum(xs) for e in self.es)
+
+    def dual(self) -> Expr:
+        return Or([e.dual() for e in self.es])
+
+
+class QuorumSystem:
+    def __init__(self, reads, writes) -> None:
+        pass
+
+
+a = Node('a')
+b = Node('b')
+c = Node('c')
+disjunction = a + b + c
+conjunction = disjunction * disjunction * disjunction
+print(conjunction)
+print(conjunction.dual())
+print(conjunction.dual().dual())