fix [expr]: Fixed empty expressions bug

src/stdlib/primitive/Array/lib.es6

@@ -2,6 +2,7 @@ import api from '../../api';
 
 export default new Map([
     require('./lib/len')(api),
+    require('./lib/fuse')(api),
     require('./lib/join')(api),
     require('./lib/each')(api),
     require('./lib/map')(api),

src/stdlib/primitive/Array/lib/join.es6

@@ -30,6 +30,5 @@ export default (api) => ["join", api.var(new api.func(
         }
 
         return api.init(api.string, stringified);
-
     }
 ))];

src/tokenizer/parsers/expr.es6

@@ -78,14 +78,18 @@ expr -> A B*/
 
 let UNARY = CheddarCustomLexer(O, true);
 
+class CheddarExpressionToken extends CheddarLexer {
+    get isExpression() { return true; }
+}
+
+let E = CheddarCustomLexer(CheddarExpressionToken, true);
+
 class CheddarExpressionTokenAlpha extends CheddarLexer {
     exec() {
         this.open(false);
 
         this.jumpWhite();
 
-        const E = CheddarExpressionToken;
-
         return this.grammar(true,
             [F],
             ['(', E, ')'],
@@ -115,17 +119,17 @@ class CheddarExpressionTokenBeta extends CheddarLexer {
     get isExpression() { return true; }
 }
 
-export default class CheddarExpressionToken extends CheddarLexer {
-    exec() {
-        this.open(false);
+CheddarExpressionToken.prototype.exec = function(empty) {
+    this.open(false);
 
-        this.jumpWhite();
+    this.jumpWhite();
 
-        return this.grammar(true,
-            [CheddarExpressionTokenAlpha, CheddarExpressionTokenBeta],
-            [] // ε
-        );
+    let GRAMMAR = [CheddarExpressionTokenAlpha, CheddarExpressionTokenBeta];
+    if (empty) {
+        return this.grammar(true, GRAMMAR);
+    } else {
+        return this.grammar(true, GRAMMAR, [/* ε */]);
     }
+};
 
-    get isExpression() { return true; }
-}
+export default CheddarExpressionToken;

src/tokenizer/states/if.es6

@@ -1,5 +1,6 @@
 import CheddarExpressionToken from './expr';
 import CheddarCodeblock from '../patterns/block';
+import CheddarCustomLexer from '../parsers/custom';
 import CheddarLexer from '../patterns/EXPLICIT';
 import * as CheddarError from '../consts/err';
 
@@ -12,8 +13,10 @@ export default class StatementIf extends CheddarLexer {
 
         this.jumpLiteral("if");
 
+        let EXPRESSION = CheddarCustomLexer(CheddarExpressionToken, true);
+
         // Match the `expr { block }` format
-        let FORMAT = [CheddarExpressionToken, CheddarCodeblock, CheddarError.EXPECTED_BLOCK];
+        let FORMAT = [EXPRESSION, CheddarCodeblock, CheddarError.EXPECTED_BLOCK];
 
         // Match initial `if`
         let IF = this.grammar(true, FORMAT);