Is operator with binding defaults using =

defaults.diff

diff --git a/src/main/php/lang/ast/syntax/php/IsOperator.class.php b/src/main/php/lang/ast/syntax/php/IsOperator.class.php
index 7e34fc1..1013b29 100755
--- a/src/main/php/lang/ast/syntax/php/IsOperator.class.php
+++ b/src/main/php/lang/ast/syntax/php/IsOperator.class.php
@@ -14,6 +14,7 @@ use lang\ast\nodes\{
   MatchExpression,
   OffsetExpression,
   ScopeExpression,
+  TernaryExpression,
   Variable
 };
 use lang\ast\syntax\Extension;
@@ -70,6 +71,11 @@ class IsOperator implements Extension {
           $parse->forward();
           $r->restriction= $pattern($parse, $types);
         }
+
+        if ('=' === $parse->token->value) {
+          $parse->forward();
+          return new IsOptional($r, $types->expression($parse, 0));
+        }
         return $r;
       } else if ('>' === $parse->token->value || '>=' === $parse->token->value || '<' === $parse->token->value || '<=' === $parse->token->value) {
         $operator= $parse->token->value;
@@ -220,11 +226,11 @@ class IsOperator implements Extension {
           new BinaryExpression($use, $pattern->operator, $pattern->value)
         );
       } else if ($pattern instanceof IsNullable) {
-        return new BinaryExpression(
+        return new Braced(new BinaryExpression(
           new BinaryExpression(new Literal('null'), '===', $init),
           '||',
           $match($codegen, $use, $pattern->element)
-        );
+        ));
       } else if ($pattern instanceof IsCompound) {
         $compound= $match($codegen, $init, $pattern->patterns[0]);
         for ($i= 1, $s= sizeof($pattern->patterns), $op= $pattern->operator.$pattern->operator; $i < $s; $i++) {
@@ -242,22 +248,39 @@ class IsOperator implements Extension {
         }
         return $compound;
       } else if ($pattern instanceof IsArrayStructure) {
-        $compound= new BinaryExpression(
-          new InvokeExpression(new Literal('is_array'), [$init]),
-          '&&',
-          new BinaryExpression(
-            new InvokeExpression(new Literal('sizeof'), [$use]),
-            $pattern->rest ? '>=' : '===',
-            new Literal((string)sizeof($pattern->patterns))
-          )
-        );
+        $size= new BinaryExpression(
+          new InvokeExpression(new Literal('sizeof'), [$use]),
+          $pattern->rest ? '>=' : '===',
+          new Literal((string)sizeof($pattern->patterns))
+         );
+        $compound= new BinaryExpression(new InvokeExpression(new Literal('is_array'), [$init]), '&&', $size);
+        $optional= 0;
         foreach ($pattern->patterns as $key => $p) {
           $offset= new Literal((string)$key);
-          $compound= new BinaryExpression($compound, '&&', new BinaryExpression(
-            new InvokeExpression(new Literal('array_key_exists'), [$offset, $use]),
-            '&&',
-            $match($codegen, new OffsetExpression($use, $offset), $p),
-          ));
+          $exists= new InvokeExpression(new Literal('array_key_exists'), [$offset, $use]);
+
+          if ($p instanceof IsOptional) {
+            $test= new Braced(new TernaryExpression(
+              $exists,
+              $match($codegen, new OffsetExpression($use, $offset), $p->binding),
+              $match($codegen, $p->default, $p->binding)
+            ));
+            $optional++;
+          } else {
+            $test= new BinaryExpression(
+              $exists,
+              '&&',
+              $match($codegen, new OffsetExpression($use, $offset), $p),
+            );
+          }
+
+          $compound= new BinaryExpression($compound, '&&', $test);
+        }
+
+        // Optional implies rest
+        if ($optional) {
+          $size->operator= '>=';
+          $size->right->expression= (string)($size->right->expression - $optional);
         }
         return $compound;
       }
diff --git a/src/test/php/lang/ast/syntax/php/unittest/VariableBindingTest.class.php b/src/test/php/lang/ast/syntax/php/unittest/VariableBindingTest.class.php
index 3c02f5e..c675450 100755
--- a/src/test/php/lang/ast/syntax/php/unittest/VariableBindingTest.class.php
+++ b/src/test/php/lang/ast/syntax/php/unittest/VariableBindingTest.class.php
@@ -115,4 +115,13 @@ class VariableBindingTest extends EmittingTest {
       }
     }'));
   }
+
+  #[Test, Values([[['key' => 1], null], [[], ['matched' => null]], [['key' => 'value'], ['matched' => 'value']]])]
+  public function with_default($input, $expected) {
+    Assert::equals($expected, $this->run('class %T {
+      public function run($input) {
+        return $input is ["key" => $expr & ?string = null] ? ["matched" => $expr] : null;
+      }
+    }', $input));
+  }
 }
\ No newline at end of file

IsOptional.class.php

<?php namespace lang\ast\syntax\php;

use lang\ast\Type;
use util\Objects;

class IsOptional extends Type {
  public $binding, $default;

  /**
   * Creates a an optional binding "type"
   *
   * @param  lang.ast.syntax.php.IsBinding $binding
   * @param  lang.ast.Node $default
   */
  public function __construct($binding, $default) {
    $this->binding= $binding;
    $this->default= $default;
  }

  /** @return string */
  public function toString() {
    return nameof($this).'('.$this->binding->toString().' ?? '.Objects::stringOf($this->default).')';
  }
}