conlang: Add unconditional loop expression, for desugaring

cl-token/src/token_type.rs

@@ -26,6 +26,7 @@ pub enum TokenKind {
     Impl,
     In,
     Let,
+    Loop,
     Mod,
     Mut,
     Pub,
@@ -122,6 +123,7 @@ impl Display for TokenKind {
             TokenKind::Impl => "impl".fmt(f),
             TokenKind::In => "in".fmt(f),
             TokenKind::Let => "let".fmt(f),
+            TokenKind::Loop => "loop".fmt(f),
             TokenKind::Mod => "mod".fmt(f),
             TokenKind::Mut => "mut".fmt(f),
             TokenKind::Pub => "pub".fmt(f),
@@ -158,6 +160,7 @@ impl FromStr for TokenKind {
             "impl" => Self::Impl,
             "in" => Self::In,
             "let" => Self::Let,
+            "loop" => Self::Loop,
             "mod" => Self::Mod,
             "mut" => Self::Mut,
             "pub" => Self::Pub,