fix: zaach/jison-lex#23 -- added basic support for JavaScript Arrow F…

…unctions in the lexer spec, both simple functions, e.g. `() => 'TOKEN'` and "complex/multiline" arrow functions, e.g. `() => { statements; return 'TOKEN'; ... }`

packages/jison-lex/regexp-lexer.js

@@ -304,8 +304,18 @@ function prepareRules(dict, actions, caseHelper, tokens, startConditions, opts)
         newRules.push(m);
         action = rule[1];
         if (typeof action === 'function') {
-            // TODO: also cope with Arrow Functions (and inline those as well?) -- see also https://github.com/zaach/jison-lex/issues/23
-            action = String(action).replace(/^\s*function\s*\(\)\s?\{/, '').replace(/\}\s*$/, '');
+            // Also cope with Arrow Functions (and inline those as well?).
+            // See also https://github.com/zaach/jison-lex/issues/23
+            action = String(action);
+            if (action.match(/^\s*function\s*\(\)\s*\{/)) {
+                action = action.replace(/^\s*function\s*\(\)\s*\{/, '').replace(/\}\s*$/, '');
+            } else if (action.match(/^\s*\(\)\s*=>[\s\r\n]*[^\s\r\n\{]/)) {
+                // () => 'TOKEN'    --> return 'TOKEN' 
+                action = action.replace(/^\s*\(\)\s*=>/, 'return ');
+            } else if (action.match(/^\s*\(\)\s*=>[\s\r\n]*\{/)) {
+                // () => { statements }     --> statements   (ergo: 'inline' the given function) 
+                action = action.replace(/^\s*\(\)\s*=>[\s\r\n]*\{/, '').replace(/\}\s*$/, '');
+            }
         }
         action = action.replace(/return\s*'((?:\\'|[^']+)+)'/g, tokenNumberReplacement);
         action = action.replace(/return\s*"((?:\\"|[^"]+)+)"/g, tokenNumberReplacement);