ascent_base 0.8.1

support library for the ascent package
Documentation 
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use std::cmp::Ordering;

use super::{BoundedLattice, Lattice};

/// A flat `Lattice`: `Bottom` <= everything <= `Top`, and `Constant(x) == Constant(y)` iff `x == y`
#[derive(PartialEq, Eq, Clone, Copy, Debug, Hash)]
#[allow(dead_code)]
pub enum ConstPropagation<T> {
   Bottom,
   Constant(T),
   Top,
}

impl<T: PartialEq> PartialOrd for ConstPropagation<T> {
   fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
      use ConstPropagation::*;
      match (self, other) {
         (Bottom, Bottom) => Some(Ordering::Equal),
         (Bottom, _) => Some(Ordering::Less),
         (Constant(_x), Bottom) => Some(Ordering::Greater),
         (Constant(x), Constant(y)) =>
            if x == y {
               Some(Ordering::Equal)
            } else {
               None
            },
         (Constant(_), Top) => Some(Ordering::Less),
         (Top, Top) => Some(Ordering::Equal),
         (Top, _) => Some(Ordering::Greater),
      }
   }
}

impl<T: PartialEq> Lattice for ConstPropagation<T> {
   fn meet(self, other: Self) -> Self {
      use ConstPropagation::*;
      match (self, other) {
         (Bottom, _) => Self::Bottom,
         (Constant(_x), Bottom) => Self::Bottom,
         (Constant(x), Constant(y)) =>
            if x == y {
               Constant(x)
            } else {
               Self::Bottom
            },
         (Constant(x), Top) => Constant(x),
         (Top, other) => other,
      }
   }

   fn join(self, other: Self) -> Self {
      use ConstPropagation::*;
      match (self, other) {
         (Bottom, other) => other,
         (Constant(x), Bottom) => Constant(x),
         (Constant(x), Constant(y)) =>
            if x == y {
               Constant(x)
            } else {
               Self::Top
            },
         (Constant(_x), Top) => Top,
         (Top, _) => Top,
      }
   }

   fn meet_mut(&mut self, other: Self) -> bool {
      use ConstPropagation::*;
      match (self, other) {
         (Bottom, _) => false,
         (Constant(x), Constant(y)) if x == &y => false,
         (this @ Constant(_), Bottom | Constant(_)) => {
            *this = Bottom;
            true
         },
         (_, Top) => false,
         (this @ Top, other) => {
            *this = other;
            true
         },
      }
   }

   fn join_mut(&mut self, other: Self) -> bool {
      use ConstPropagation::*;
      match (self, other) {
         (_, Bottom) => false,
         (this @ Bottom, other) => {
            *this = other;
            true
         },
         (Constant(x), Constant(y)) if x == &y => false,
         (this @ Constant(_), Constant(_) | Top) => {
            *this = Top;
            true
         },
         (Top, _) => false,
      }
   }
}

impl<T: Lattice> BoundedLattice for ConstPropagation<T>
where ConstPropagation<T>: Lattice
{
   fn top() -> Self { Self::Top }
   fn bottom() -> Self { Self::Bottom }
}

#[test]
fn test_constant_propagation() {
   let const_1 = ConstPropagation::Constant(1);
   assert!(const_1 > ConstPropagation::Bottom);
   assert!(const_1 < ConstPropagation::Top);
   assert!(const_1 > ConstPropagation::bottom());
}

#[test]
fn test_constant_propagation_lattice() {
   let const_1 = ConstPropagation::Constant(1);

   let mut x = const_1;
   assert!(!x.join_mut(const_1));
   assert!(!x.meet_mut(const_1));
   assert!(!x.join_mut(ConstPropagation::Bottom));
   assert!(!x.meet_mut(ConstPropagation::Top));

   assert!(x == const_1);

   assert!(x.join_mut(ConstPropagation::Constant(2)));

   assert_eq!(x, ConstPropagation::Top);

   assert!(!x.join_mut(ConstPropagation::Constant(2)));
}