ast: support parenthesized subexpressions

src/ast/mod.rs

@@ -248,6 +248,10 @@ impl Parser {
     fn parse_primary_expr(&mut self) -> Result<tree::Node, Error> {
         let token = self.lexer.require_next()?;
         match token.kind {
+            token::Kind::OParen => {
+                let expr = self.parse_binary_expr_or_higher(&[token::Kind::CParen])?;
+                self.parse_primary_expr_rest(expr)
+            },
             token::Kind::Ident => {
                 let ident = tree::Node::Ident(String::from(token.raw));
                 self.parse_primary_expr_rest(ident)