Optimize passing constant expressions

Author: thekid

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

@@ -1,20 +1,25 @@
 <?php namespace lang\ast\emit;
 
-use lang\ast\nodes\Placeholder;
+use lang\ast\nodes\{Placeholder, Variable, UnpackExpression};
 
 /**
  * Rewrites partial function application as follows:
  * 
  * ```php
  * // Input:
- * $f= str_replace('test', result(), ?);
+ * $f= str_replace('test', 'ok', ?);
  * 
+ * // Output:
+ * $f= fn($arg) => str_replace('test', 'ok', $arg);
+ *
+ * // Input:
+ * $f= str_replace('test', result(), ?);
+ *
  * // Ouput:
  * $f= [
- *   $a0= 'test',
- *   $a1= result(),
- *   fn($arg) => str_replace($a0, $a1, $arg)
- * ][2];
+ *   $temp= result(),
+ *   fn($arg) => str_replace('test', $temp, $arg)
+ * ][1];
  * ```
  *
  * @see  https://wiki.php.net/rfc/partial_function_application_v2
@@ -23,31 +28,43 @@ trait RewritePartialFunctionApplications {
 
   protected function emitCallable($result, $callable) {
     if ([Placeholder::$VARIADIC] !== $callable->arguments) {
-      $sig= $pass= '';
-      $offset= 0;
-      $result->out->write('[');
+      $sig= '';
+      $pass= $init= [];
       foreach ($callable->arguments as $argument) {
-        $t= $result->temp();
         if (Placeholder::$VARIADIC === $argument) {
+          $t= $result->temp();
           $sig.= ',...'.$t;
-          $pass.= ',...'.$t;
+          $pass[]= new UnpackExpression(new Variable(substr($t, 1)));
         } else if (Placeholder::$ARGUMENT === $argument) {
+          $t= $result->temp();
           $sig.= ','.$t;
-          $pass.= ','.$t;
+          $pass[]= new Variable(substr($t, 1));
+        } else if ($this->isConstant($result, $argument)) {
+          $pass[]= $argument;
         } else {
-          $pass.= ','.$t;
+          $t= $result->temp();
+          $pass[]= new Variable(substr($t, 1));
+          $init[$t]= $argument;
+        }
+      }
+
+      // Initialize any non-constant expressions in place
+      if ($init) {
+        $result->out->write('[');
+        foreach ($init as $t => $argument) {
           $result->out->write($t.'=');
           $this->emitOne($result, $argument);
           $result->out->write(',');
-          $offset++;
         }
       }
 
+      // Emit closure invoking the callable expression
       $result->out->write('fn('.substr($sig, 1).')=>');
       $this->emitOne($result, $callable->expression);
-      $result->out->write('('.substr($pass, 1).')');
-
-      $result->out->write(']['.$offset.']');
+      $result->out->write('(');
+      $this->emitArguments($result, $pass);
+      $result->out->write(')');
+      $init && $result->out->write(']['.sizeof($init).']');
     } else {
       parent::emitCallable($result, $callable);
     }