conlang: Add unconditional loop expression, for desugaring

cl-ast/src/ast_impl.rs

@@ -367,6 +367,7 @@ mod display {
                 ExprKind::Empty => "()".fmt(f),
                 ExprKind::Group(v) => v.fmt(f),
                 ExprKind::Tuple(v) => v.fmt(f),
+                ExprKind::Loop(v) => v.fmt(f),
                 ExprKind::While(v) => v.fmt(f),
                 ExprKind::If(v) => v.fmt(f),
                 ExprKind::For(v) => v.fmt(f),
@@ -534,6 +535,12 @@ mod display {
             write!(f, "({})", self.expr)
         }
     }
+    impl Display for Loop {
+        fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+            let Self { body } = self;
+            write!(f, "loop {body}")
+        }
+    }
     impl Display for While {
         fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
             let Self { cond, pass, fail } = self;

cl-ast/src/lib.rs

@@ -346,6 +346,8 @@ pub enum ExprKind {
     Group(Group),
     /// A [Tuple] expression: `(` [`Expr`] (`,` [`Expr`])+ `)`
     Tuple(Tuple),
+    /// A [Loop] expression: `loop` [`Block`]
+    Loop(Loop),
     /// A [While] expression: `while` [`Expr`] [`Block`] [`Else`]?
     While(While),
     /// An [If] expression: `if` [`Expr`] [`Block`] [`Else`]?
@@ -492,6 +494,12 @@ pub struct Tuple {
     pub exprs: Vec<Expr>,
 }
 
+/// A [Loop] expression: `loop` [`Block`]
+#[derive(Clone, Debug, PartialEq, Eq, Hash)]
+pub struct Loop {
+    pub body: Block,
+}
+
 /// A [While] expression: `while` [`Expr`] [`Block`] [`Else`]?
 #[derive(Clone, Debug, PartialEq, Eq, Hash)]
 pub struct While {