lang: rewrite parser

crates/lang/src/parser/grammar.rs

@@ -0,0 +1,14 @@
+use crate::parser::syntax_kind::SyntaxKind::*;
+
+use super::Parser;
+
+mod expression;
+
+pub fn source_file(p: &mut Parser) {
+    let root = p.start();
+
+    expression::expression(p);
+    p.eat_succeeding_ws();
+
+    root.complete(p, ROOT);
+}