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/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at https://mozilla.org/MPL/2.0/. */
//! Kleen logic: https://en.wikipedia.org/wiki/Three-valued_logic#Kleene_and_Priest_logics
/// A "trilean" value based on Kleen logic.
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub enum KleeneValue {
/// False
False = 0,
/// True
True = 1,
/// Either true or false, but we’re not sure which yet.
Unknown,
}
impl From<bool> for KleeneValue {
fn from(b: bool) -> Self {
if b {
Self::True
} else {
Self::False
}
}
}
impl KleeneValue {
/// Turns this Kleene value to a bool, taking the unknown value as an
/// argument.
pub fn to_bool(self, unknown: bool) -> bool {
match self {
Self::True => true,
Self::False => false,
Self::Unknown => unknown,
}
}
/// Return true if any result of f() is true. Otherwise, return the strongest value seen.
/// Returns false if empty, like that of `Iterator`.
#[inline(always)]
pub fn any<T>(
iter: impl Iterator<Item = T>,
f: impl FnMut(T) -> Self,
) -> Self {
Self::any_value(iter, Self::True, Self::False, f)
}
/// Return false if any results of f() is false. Otherwise, return the strongest value seen.
/// Returns true if empty, opposite of `Iterator`.
#[inline(always)]
pub fn any_false<T>(
iter: impl Iterator<Item = T>,
f: impl FnMut(T) -> Self,
) -> Self {
Self::any_value(iter, Self::False, Self::True, f)
}
#[inline(always)]
fn any_value<T>(
iter: impl Iterator<Item = T>,
value: Self,
on_empty: Self,
mut f: impl FnMut(T) -> Self,
) -> Self {
let mut result = None;
for item in iter {
let r = f(item);
if r == value {
return r;
}
if let Some(v) = result.as_mut() {
*v = *v & r;
} else {
result = Some(r);
}
}
result.unwrap_or(on_empty)
}
}
impl std::ops::Not for KleeneValue {
type Output = Self;
fn not(self) -> Self {
match self {
Self::True => Self::False,
Self::False => Self::True,
Self::Unknown => Self::Unknown,
}
}
}
// Implements the logical and operation.
impl std::ops::BitAnd for KleeneValue {
type Output = Self;
fn bitand(self, other: Self) -> Self {
if self == Self::False || other == Self::False {
return Self::False;
}
if self == Self::Unknown || other == Self::Unknown {
return Self::Unknown;
}
Self::True
}
}
// Implements the logical or operation.
impl std::ops::BitOr for KleeneValue {
type Output = Self;
fn bitor(self, other: Self) -> Self {
if self == Self::True || other == Self::True {
return Self::True;
}
if self == Self::Unknown || other == Self::Unknown {
return Self::Unknown;
}
Self::False
}
}
impl std::ops::BitOrAssign for KleeneValue {
fn bitor_assign(&mut self, other: Self) {
*self = *self | other;
}
}
impl std::ops::BitAndAssign for KleeneValue {
fn bitand_assign(&mut self, other: Self) {
*self = *self & other;
}
}
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