Adds operators

src/ast.rs

@@ -27,7 +27,31 @@ pub enum Body
 pub enum Predicate
 {
     Variable(Variable), // Upercase variable like X
-    Fixed(String, Vec<Predicate>),
+    Fixed(Functor, Vec<Predicate>),
+}
+
+#[derive(Clone, Debug, PartialEq)]
+pub enum Functor
+{
+    Operator(Operator),
+    Functor(String),
+}
+
+#[derive(Clone, Debug, PartialEq)]
+pub enum Operator
+{
+    Plus,
+    Minus,
+    Cons,
+    Custom(String, usize, OperatorType),
+}
+
+#[derive(Clone, Debug, PartialEq, Eq, Hash)]
+pub enum OperatorType
+{
+    Prefix,
+    Postfix,
+    Infix,
 }
 
 impl Display for Body
@@ -110,3 +134,28 @@ impl Display for Module
         Ok(())
     }
 }
+
+impl Display for Functor
+{
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result
+    {
+        match self
+        {
+            Functor::Operator(op) => write!(f, "{}", op),
+            Functor::Functor(name) => write!(f, "{}", name),
+        }
+    }
+}
+impl Display for Operator
+{
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result
+    {
+        match self
+        {
+            Operator::Plus => write!(f, "+"),
+            Operator::Minus => write!(f, "-"),
+            Operator::Cons => write!(f, "::"),
+            Operator::Custom(string, _, _) => write!(f, "{}", string),
+        }
+    }
+}