Emit binary operations directly instead of deferring their initialization

See https://wiki.php.net/rfc/const_scalar_exprs

Author: thekid

src/main/php/lang/ast/emit/PHP.class.php

@@ -1,7 +1,7 @@
 <?php namespace lang\ast\emit;
 
 use lang\ast\Code;
-use lang\ast\nodes\{InstanceExpression, ScopeExpression, Variable, Literal, ArrayLiteral, Block};
+use lang\ast\nodes\{InstanceExpression, ScopeExpression, BinaryExpression, Variable, Literal, ArrayLiteral, Block};
 use lang\ast\types\{IsUnion, IsFunction, IsArray, IsMap};
 use lang\ast\{Emitter, Node, Type};
 
@@ -37,8 +37,9 @@ protected function declaration($name) {
    * - Any literal
    * - Arrays where all members are literals
    * - Scope expressions with literal members (self::class, T::const)
+   * - Binary expression where left- and right hand side are literals
    *
-   * @see    https://wiki.php.net/rfc/new_in_initializers
+   * @see    https://wiki.php.net/rfc/const_scalar_exprs
    * @param  lang.ast.Node $node
    * @return bool
    */
@@ -52,6 +53,8 @@ protected function isConstant($node) {
       return true;
     } else if ($node instanceof ScopeExpression) {
       return $node->member instanceof Literal;
+    } else if ($node instanceof BinaryExpression) {
+      return $this->isConstant($node->left) && $this->isConstant($node->right);
     }
     return false;
   }

src/test/php/lang/ast/unittest/emit/InitializeWithExpressionsTest.class.php

@@ -8,6 +8,7 @@
  *
  * @see  https://github.com/xp-framework/compiler/pull/104
  * @see  https://wiki.php.net/rfc/new_in_initializers
+ * @see  https://wiki.php.net/rfc/const_scalar_exprs
  * @see  https://wiki.php.net/rfc/calls_in_constant_expressions
  */
 class InitializeWithExpressionsTest extends EmittingTest {