adding JISON test cases as provided by zaach/jison-lex#23 (with a min…

…or tweak to test/showcase `e + e` action code expansion with named variables: `$e1 + $e2` instead of the more cryptic (old-skool yacc style action code) `$1 + $3`

examples/issue-lex-23-good.js

@@ -0,0 +1,33 @@
+// title: Parse error when using arrow function in rules
+//
+// ...
+//  
+// This is the SUCCESSFUL lexer spec
+// 
+
+let grammar = {
+    lex: {
+        rules: [
+            ['\\s+', ''],
+            ['\\d+', function () { return 'NUMBER'}],
+            ['\\+', function () { return '+' }],
+            ['$',  function () { return 'EOF' }],
+        ]
+    },
+    operators: [
+        ['left', '+']
+    ],
+    bnf: {
+        'es': [
+            ['e EOF', 'return $1']
+        ],
+        'e': [
+            ['e + e', '$$ = $e1 + $e2'],
+            ['NUMBER', '$$ = Number(yytext)']
+        ]
+    }
+};
+
+module.exports = grammar;
+// export default grammar;
+

examples/issue-lex-23-trouble.js

@@ -0,0 +1,33 @@
+// title: Parse error when using arrow function in rules
+//
+// ...
+//  
+// This is the FAILING lexer spec
+// 
+
+let grammar = {
+    lex: {
+        rules: [
+            ['\\s+', ''],
+            ['\\d+', () => 'NUMBER'],
+            ['\\+', () => '+'],
+            ['$', () => 'EOF'],
+        ]
+    },
+    operators: [
+        ['left', '+']
+    ],
+    bnf: {
+        'es': [
+            ['e EOF', 'return $1']
+        ],
+        'e': [
+            ['e + e', '$$ = $e1 + $e2'],
+            ['NUMBER', '$$ = Number(yytext)']
+        ]
+    }
+};
+
+module.exports = grammar;
+// export default grammar;
+