diff --git a/lib/Context.php b/lib/Context.php
index 1ed043b..30b25f4 100755
--- a/lib/Context.php
+++ b/lib/Context.php
@@ -44,6 +44,38 @@ private function locateGCCHeaderPaths() {
         }
     }
 
+    public function findHeaderFile(string $header, string $contextDir, string $contextFile, bool $next): ?string {
+        if ($header[0] === '/' || ($header[1] === ':' && $header[2] === '\\')) {
+            if (file_exists($header)) {
+                return $header;
+            }
+        } else {
+            if ($contextDir && !$next) {
+                $dir = $contextDir;
+                while (!empty($dir) && $dir !== '/') {
+                    $file = "$dir/$header";
+                    if (file_exists($file)) {
+                        return $file;
+                    }
+                    $dir = dirname($dir);
+                }
+            }
+            foreach ($this->headerSearchPaths as $path) {
+                if ($next) {
+                    if ($contextDir === $path) {
+                        $next = false;
+                    }
+                    break;
+                }
+                $test = $path . '/' . $header;
+                if (file_exists($test)) {
+                    return $test;
+                }
+            }
+        }
+        return null;
+    }
+
     public function getDefines(): array {
         return $this->definitions;
     }
@@ -142,7 +174,7 @@ public function evaluate(?Token $expr): Token {
                     return new Token(Token::NUMBER, '0', 'computed');
             }
             return $expr;
-        } 
+        }
         list ($result, $expr) = $this->evaluateInternal($expr);
         if ($expr !== null) {
             throw new \LogicException('Syntax error: unknown trailing expr: ' . $expr->value);
@@ -187,6 +219,38 @@ public function evaluateInternal(?Token $expr, bool $single = false): array {
             } else {
                 throw new \LogicException("Syntax Error for #defined expression, expecting ( or IDENTIFIER, found " . $expr->value);
             }
+        } elseif ($expr->type === Token::IDENTIFIER && $expr->value === '__has_include') {
+            $expr = Token::skipWhitespace($expr->next);
+            if ($expr === null) {
+                throw new \LogicException("Syntax Error for __has_include() expression: not enough tokens");
+            }
+            if ($expr->type === Token::PUNCTUATOR && $expr->value === '(') {
+                $expr = Token::skipWhitespace($expr->next);
+                if ($expr->type === Token::LITERAL) {
+                    $file = $expr->value;
+                } elseif ($expr->type === Token::PUNCTUATOR && $expr->value === '<') {
+                    // handle <> include:
+                    $file = '';
+                    while (!empty($expr->next)) {
+                        $expr = $expr->next;
+                        if ($expr->type === Token::PUNCTUATOR && $expr->value === '>') {
+                            break;
+                        }
+                        $file .= $expr->value;
+                    }
+                } else {
+                    throw new \LogicException("Syntax Error for __has_include() expression, expecting < or LITERAL, found " . $expr->value);
+                }
+                $expr = Token::skipWhitespace($expr->next);
+                if ($expr === null || $expr->type !== Token::PUNCTUATOR && $expr->value !== ')') {
+                    throw new \LogicException("Syntax Error for __has_include() expression: ) not found");
+                }
+                $contextDir = dirname($expr->file);
+                $result = new Token(Token::NUMBER, $this->findHeaderFile($file, $contextDir, $expr->file, false) !== null ? '1' : '0', 'computed');
+                $expr = Token::skipWhitespace($expr->next);
+            } else {
+                throw new \LogicException("Syntax Error for #__has_include expression, expecting (, found " . $expr->value);
+            }
         } elseif ($expr->type === Token::IDENTIFIER) {
             $next = Token::skipWhitespace($expr->next);
             if ($next !== null && $next->value === '(') {
@@ -221,6 +285,7 @@ public function evaluateInternal(?Token $expr, bool $single = false): array {
             $result = new Token(Token::NUMBER, $expr->value, 'computed');
             $expr = Token::skipWhitespace($expr->next);
         } else {
+            var_dump($expr);
             throw new \LogicException('Unknown operator ' . $expr->value);
         }
         if ($negate) {
@@ -362,6 +427,8 @@ private function normalize(Token $expr): int {
                     throw new \LogicException("Base mismatch for {$str}, found $chr for $idx");
                 }
                 $result = ($result * $base) + $chr;
+            } elseif ($str[$idx] === 'U') {
+                // unsigned number, let's not touch it
             } elseif ($str[$idx] === 'L') {
                 // indicates number is a long, return as is
                 if ($idx + 1 !== $length) {
@@ -389,7 +456,28 @@ public function doCall(string $toCall, ?Token ...$args): Token {
         $argIdx = 0;
         if ($token->value === '(') {
             $token = Token::skipWhitespace($token->next);
+            $isVariadic = false;
             while ($token !== null && $token->value !== ')') {
+                if ($isVariadic) {
+                    throw new \LogicException('Unexpected token found, expecting ) after ... found ' . $token->value);
+                }
+                if ($token->type === Token::PUNCTUATOR && $token->value === "...") {
+                    $isVariadic = true;
+                    if (isset($args[$argIdx])) {
+                        $argMap["__VA_ARGS__"] = $variadic = $args[$argIdx++];
+                        while (isset($args[$argIdx])) {
+                            while ($variadic->next) {
+                                $variadic = $variadic->next;
+                            }
+                            $variadic->next = $args[$argIdx++];
+                        }
+                    } else {
+                        $argMap["__VA_ARGS__"] = new Token(Token::OTHER, '', 'computed');
+                    }
+                    $token = Token::skipWhitespace($token->next);
+                    continue;
+                }
+
                 if ($token->type !== Token::IDENTIFIER) {
                     throw new \LogicException('Unexpected argument found, expecting IDENTIFIER found ' . $token->value);
                 } elseif (!array_key_exists($argIdx, $args)) {
@@ -413,6 +501,16 @@ public function doCall(string $toCall, ?Token ...$args): Token {
         // Copy token stream
         $first = $newToken = new Token(0, '', 'internal');
         while ($token !== null) {
+            // handle , ##__VA_ARGS__
+            if ($token->type === Token::PUNCTUATOR && $token->value === ',') {
+                $nextToken = Token::skipWhitespace($token);
+                if ($nextToken->type === Token::PUNCTUATOR && $token->value === '##') {
+                    if (\count($argMap) > $argIdx) {
+                        $newToken = $newToken->next = new Token($token->type, $token->value, $token->file);
+                    }
+                    $token = Token::skipWhitespace($nextToken);
+                }
+            }
             if ($token->type === Token::IDENTIFIER && array_key_exists($token->value, $argMap)) {
                 $arg = $argMap[$token->value];
                 $toAdd = $toAddNext = new Token(Token::OTHER, '', 'computed');
diff --git a/lib/PreProcessor.php b/lib/PreProcessor.php
index f08761f..6ad936f 100755
--- a/lib/PreProcessor.php
+++ b/lib/PreProcessor.php
@@ -50,6 +50,10 @@ public function process(string $header): array {
                         $tokens = $this->resolveInclude($line, $directive->file);
                         $lines = array_merge($tokens, $lines);
                         break;
+                    case 'include_next':
+                        $tokens = $this->resolveInclude($line, $directive->file, true);
+                        $lines = array_merge($tokens, $lines);
+                        break;
                     case 'define':
                         if (empty($line)) {
                             throw new \LogicException("#define must have a name");
@@ -100,19 +104,33 @@ public function process(string $header): array {
                         break;
                     case 'else':
                     case 'elif':
-                        $lines = $this->skipIf($lines);
+                        $lines = $this->skipIf($lines, true);
                         break;
                     case 'endif':
                         // ignore
                         break;
+                    case 'pragma':
+                        if (empty($line)) {
+                            throw new \LogicException("At least one declaration is required for pragma");
+                        }
+                        $pragmaMode = $line;
+                        if ($pragmaMode->value === "once") {
+                            if (Token::skipWhitespace($pragmaMode->next)) {
+                                throw new \LogicException("pragma once has no further arguments");
+                            }
+                            $this->headers[$pragmaMode->file] = true;
+                        }
+                        break;
                     case 'warning':
                         // ignore
                         break;
                     case 'error':
-                        var_dump($this->context);
+                        //var_dump($this->context);
+                        //var_dump(array_keys($this->context->getDefines()));
                         $this->debug($directive);
                         throw new \LogicException('We reached an error preprocessor token:');
                     default:
+                        var_dump($line);
                         var_dump($directive->value);
                         throw new \LogicException("Unknown directive found {$directive->value}");
                 }
@@ -173,6 +191,7 @@ private function skipIf(array $lines, bool $skipAll = false): array {
                             return $lines;
                         case 'define':
                         case 'include':
+                        case 'pragma': // there are no special pragmas supposed to be in #if's
                         case 'undef':
                         case 'error':
                         case 'warning':
@@ -187,15 +206,19 @@ private function skipIf(array $lines, bool $skipAll = false): array {
         return [];
     }
 
-    private function findAndParse(string $header, string $contextDir, string $contextFile): array {
+    private function findAndParse(string $header, string $contextDir, string $contextFile, bool $next = false): array {
         $contextDir = rtrim($contextDir, '/');
-        $file = $this->findHeaderFile($header, $contextDir, $contextFile);
+        $file = $this->findHeaderFile($header, $contextDir, $contextFile, $next);
+        if (($this->headers[$file] ?? false) === true) { // has pragma once
+            return [];
+        }
+        $this->headers[$file] = false;
         $code = file_get_contents($file);
         $lines = $this->parser->parse($file, $code);
         return $lines;
     }
 
-    private function resolveInclude(?Token $arg, string $contextFile): array {
+    private function resolveInclude(?Token $arg, string $contextFile, bool $next = false): array {
         $contextDir = dirname($contextFile);
         if (empty($arg)) {
             throw new \LogicException("Empty include declaration");
@@ -204,9 +227,9 @@ private function resolveInclude(?Token $arg, string $contextFile): array {
         if ($type->type === Token::LITERAL) {
             $file = $type->value;
             if (!empty($args)) {
-                throw new \LogicException("extra tokens in #include directive");
+                throw new \LogicException("extra tokens in #include" . ($next ? "_next" : "") . " directive");
             }
-            return $this->findAndParse($file, $contextDir, $contextFile);
+            return $this->findAndParse($file, $contextDir, $contextFile, $next);
         } elseif ($type->type === Token::PUNCTUATOR && $type->value === '<' && !empty($arg->next)) {
             // handle <> include:
             $file = '';
@@ -218,44 +241,28 @@ private function resolveInclude(?Token $arg, string $contextFile): array {
                 $file .= $arg->value;
             }
             if (!empty($args)) {
-                throw new \LogicException("extra tokens in #include directive");
+                throw new \LogicException("extra tokens in #include" . ($next ? "_next" : "") . " directive");
             }
             // always a system import
-            return $this->findAndParse($file, $contextDir, $contextFile);
+            return $this->findAndParse($file, $contextDir, $contextFile, $next);
         }
         var_dump($type, $arg);
         throw new \LogicException("Illegal include directive");
     }
 
-    private function findHeaderFile(string $header, string $contextDir, string $contextFile): string {
-        if ($header[0] === '/' || ($header[1] === ':' && $header[2] === '\\')) {
-            if (file_exists($header)) {
-                return $header;
-            }
-        } else {
-            if ($contextDir) {
-                $dir = $contextDir;
-                while (!empty($dir) && $dir !== '/') {
-                    $file = "$dir/$header";
-                    if (file_exists($file)) {
-                        return $file;
-                    }
-                    $dir = dirname($dir);
-                }
-            }
-            foreach ($this->context->headerSearchPaths as $path) {
-                $test = $path . '/' . $header;
-                if (file_exists($test)) {
-                    return $test;
-                }
-            }
-        }
+    private function findHeaderFile(string $header, string $contextDir, string $contextFile, bool $next): string {
+        if ($headerFile = $this->context->findHeaderFile($header, $contextDir, $contextFile, $next)) {
+            return $headerFile;
+        } 
         var_dump($this->context->headerSearchPaths);
         throw new \LogicException("Could not find header file: $header given context $contextDir (called from $contextFile)");
     }
 
     private function debug(?Token $token): void {
         echo "T: ";
+        if ($token) {
+            echo "@{$token->file} :";
+        }
         while ($token !== null) {
             echo $token->value . ' ';
             $token = $token->next;
@@ -401,4 +408,4 @@ public function nextArg(): void {
         $this->args[] = $this->currentArg->next;
         $this->currentArg = new Token(0, '', 'internal');
     }
-}
+}
\ No newline at end of file
diff --git a/test/cases/c/elifchain.phpt b/test/cases/c/elifchain.phpt
new file mode 100755
index 0000000..a0ea5c2
--- /dev/null
+++ b/test/cases/c/elifchain.phpt
@@ -0,0 +1,16 @@
+--TEST--
+Test for #elif chains
+--FILE--
+
+#if 0
+#elif 1
+#elif 0
+#elif 0
+#else
+#error "ERROR"
+#endif
+
+int bar;
+
+--EXPECT--
+int bar;
diff --git a/test/cases/c/pragma_once.phpt b/test/cases/c/pragma_once.phpt
new file mode 100755
index 0000000..43c7187
--- /dev/null
+++ b/test/cases/c/pragma_once.phpt
@@ -0,0 +1,11 @@
+--TEST--
+Test for #elif chains
+--FILE--
+
+#include "pragma_once.h"
+#include "pragma_once.h"
+
+int TEST;
+
+--EXPECT--
+int bar;
diff --git a/test/generated/c/elifchainTest.c b/test/generated/c/elifchainTest.c
new file mode 100644
index 0000000..f89be25
--- /dev/null
+++ b/test/generated/c/elifchainTest.c
@@ -0,0 +1,11 @@
+
+#if 0
+#elif 1
+#elif 0
+#elif 0
+#else
+#error "ERROR"
+#endif
+
+int bar;
+
diff --git a/test/generated/c/elifchainTest.php b/test/generated/c/elifchainTest.php
new file mode 100644
index 0000000..91afa89
--- /dev/null
+++ b/test/generated/c/elifchainTest.php
@@ -0,0 +1,34 @@
+<?php declare(strict_types=1);
+namespace PHPCParser\Test\c;
+use PHPCParser\CParser;
+use PHPCParser\Printer;
+use PHPCParser\Printer\Dumper;
+use PHPCParser\Printer\C;
+use PHPUnit\Framework\TestCase;
+
+/**
+ * Note: this is a generated file, do not edit this!!!
+ */
+class elifchainTest extends TestCase {
+
+    const EXPECTED = 'int bar;';
+
+    protected CParser $parser;
+    protected Printer $printer;
+
+    public function setUp(): void {
+        $this->parser = new CParser;
+        $this->parser->addSearchPath(__DIR__);
+        $this->parser->addSearchPath(__DIR__ . '/../../include');
+        $this->printer = new C;
+    }
+
+    /**
+     * @textdox Test for #elif chains
+     */
+    public function testCode() {
+        $translationUnit = $this->parser->parse(__DIR__ . '/elifchainTest.c');
+        $actual = $this->printer->print($translationUnit);
+        $this->assertEquals(self::EXPECTED, trim($actual));
+    }
+}
\ No newline at end of file
diff --git a/test/generated/c/pragma_onceTest.c b/test/generated/c/pragma_onceTest.c
new file mode 100644
index 0000000..f4b74e2
--- /dev/null
+++ b/test/generated/c/pragma_onceTest.c
@@ -0,0 +1,6 @@
+
+#include "pragma_once.h"
+#include "pragma_once.h"
+
+int TEST;
+
diff --git a/test/generated/c/pragma_onceTest.php b/test/generated/c/pragma_onceTest.php
new file mode 100644
index 0000000..3da2e55
--- /dev/null
+++ b/test/generated/c/pragma_onceTest.php
@@ -0,0 +1,34 @@
+<?php declare(strict_types=1);
+namespace PHPCParser\Test\c;
+use PHPCParser\CParser;
+use PHPCParser\Printer;
+use PHPCParser\Printer\Dumper;
+use PHPCParser\Printer\C;
+use PHPUnit\Framework\TestCase;
+
+/**
+ * Note: this is a generated file, do not edit this!!!
+ */
+class pragma_onceTest extends TestCase {
+
+    const EXPECTED = 'int bar;';
+
+    protected CParser $parser;
+    protected Printer $printer;
+
+    public function setUp(): void {
+        $this->parser = new CParser;
+        $this->parser->addSearchPath(__DIR__);
+        $this->parser->addSearchPath(__DIR__ . '/../../include');
+        $this->printer = new C;
+    }
+
+    /**
+     * @textdox Test for #elif chains
+     */
+    public function testCode() {
+        $translationUnit = $this->parser->parse(__DIR__ . '/pragma_onceTest.c');
+        $actual = $this->printer->print($translationUnit);
+        $this->assertEquals(self::EXPECTED, trim($actual));
+    }
+}
\ No newline at end of file
diff --git a/test/include/pragma_once.h b/test/include/pragma_once.h
new file mode 100644
index 0000000..8171ef2
--- /dev/null
+++ b/test/include/pragma_once.h
@@ -0,0 +1,8 @@
+
+#ifdef TEST
+#error "VERY BAD"
+#endif
+
+#pragma once
+
+#define TEST "bar"