minimal working grammar

grammar.js

@@ -2,7 +2,20 @@ module.exports = grammar({
   name: 'nixshell',
 
   rules: {
-    // TODO: add the actual grammar rules
-    source_file: $ => 'hello'
+    source_file: $ => seq($.first_line, repeat($.non_first_line)),
+
+    first_line: $ => seq($.shebang_open, $.opt_ws, optional(seq($.env, $.ws)), $.nix_shell),
+    non_first_line: $ => seq($.newline, $.annotation_line),
+    annotation_line: $ => seq($.shebang_open, $.opt_ws, $.nix_shell, $.nix_shell_args),
+    embedded_script_line: $ => /.*/,
+
+    shebang_open: $ => /#!/,
+    // TODO: allow `usr/bin/env`, `env`
+    env: $ => '/usr/bin/env',
+    nix_shell: $ => 'nix-shell',
+    nix_shell_args: $ => ' -i bash',
+    ws: $ => / +/,
+    opt_ws: $ => / */,
+    newline: $ => '\n',
   }
 });