Require identity equality for variable declarations

Variable declarations should only be considered equal if their identity
is equal. In other words, just because two different variable
declarations share the same name, they aren’t automatically equal. This
is to support situations in which nested variable declarations shadow
variable declarations of the same name at a higher level.

src/ast.rs

@@ -70,12 +70,51 @@ impl PredicateDeclaration
 
 pub type PredicateDeclarations = std::collections::BTreeSet<std::rc::Rc<PredicateDeclaration>>;
 
-#[derive(Eq, Hash, Ord, PartialEq, PartialOrd)]
 pub struct VariableDeclaration
 {
 	pub name: String,
 }
 
+impl std::cmp::PartialEq for VariableDeclaration
+{
+	#[inline(always)]
+	fn eq(&self, other: &VariableDeclaration) -> bool
+	{
+		let l = self as *const VariableDeclaration;
+		let r = other as *const VariableDeclaration;
+
+		l.eq(&r)
+	}
+}
+
+impl std::cmp::Eq for VariableDeclaration
+{
+}
+
+impl std::cmp::PartialOrd for VariableDeclaration
+{
+	#[inline(always)]
+	fn partial_cmp(&self, other: &VariableDeclaration) -> Option<std::cmp::Ordering>
+	{
+		let l = self as *const VariableDeclaration;
+		let r = other as *const VariableDeclaration;
+
+		l.partial_cmp(&r)
+	}
+}
+
+impl std::cmp::Ord for VariableDeclaration
+{
+	#[inline(always)]
+	fn cmp(&self, other: &VariableDeclaration) -> std::cmp::Ordering
+	{
+		let l = self as *const VariableDeclaration;
+		let r = other as *const VariableDeclaration;
+
+		l.cmp(&r)
+	}
+}
+
 impl VariableDeclaration
 {
 	pub fn new(name: String) -> Self