conlang: Add constructor expression for structs!

grammar:
- Add new rules `PathLike`, `Structor`, `Fielder`
- Replace Path with PathLike in Primary expressions

cl-ast:
- Add nodes for Structor and Fielder

cl-parser:
- Add branch to path-expression parsing
- Parse Structor bodies

interpret:
- Add TODO

compiler/cl-ast/src/ast_impl.rs

@@ -424,6 +424,7 @@ mod display {
                 ExprKind::Binary(v) => v.fmt(f),
                 ExprKind::Unary(v) => v.fmt(f),
                 ExprKind::Index(v) => v.fmt(f),
+                ExprKind::Structor(v) => v.fmt(f),
                 ExprKind::Path(v) => v.fmt(f),
                 ExprKind::Literal(v) => v.fmt(f),
                 ExprKind::Array(v) => v.fmt(f),
@@ -540,6 +541,25 @@ mod display {
         }
     }
 
+    impl Display for Structor {
+        fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+            let Self { to, init } = self;
+            write!(f, "{to}: ")?;
+            separate(init, ", ")(f.delimit(INLINE_BRACES))
+        }
+    }
+
+    impl Display for Fielder {
+        fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+            let Self { name, init } = self;
+            write!(f, "{name}")?;
+            if let Some(init) = init {
+                write!(f, ": {init}")?;
+            }
+            Ok(())
+        }
+    }
+
     impl Display for Array {
         fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
             separate(&self.values, ", ")(f.delimit(INLINE_SQUARE))