diff --git a/.travis.yml b/.travis.yml
index d0bfa28..4cfafc2 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -3,16 +3,20 @@ language: php
 php:
   - 7.0
   - 7.1
+  - 7.2
+  - 7.3
+  - 7.4snapshot
   - nightly
 
 matrix:
   allow_failures:
     - php: nightly
+    - php: 7.4snapshot
 
 sudo: false
 
 before_script:
-  - phpenv config-rm xdebug.ini
+  - phpenv config-rm xdebug.ini || true
   - composer self-update
   - composer require satooshi/php-coveralls:~2.0.0 --no-update --dev
   - composer install --prefer-source
diff --git a/Dockerfile b/Dockerfile
new file mode 100644
index 0000000..ec6d6c0
--- /dev/null
+++ b/Dockerfile
@@ -0,0 +1,27 @@
+FROM golang:1.10.1-alpine3.7 as builder
+
+WORKDIR /go/src/nubank/authorizer
+
+RUN apk --update add git openssh && \
+    rm -rf /var/lib/apt/lists/* && \
+    rm /var/cache/apk/*
+
+RUN go get -u github.com/golang/dep/cmd/dep
+
+COPY . .
+
+RUN dep ensure
+
+RUN go test -v ./...
+
+RUN go build -ldflags "-s -w" -o ./authorize
+
+FROM alpine:3.7
+
+WORKDIR /app
+
+RUN apk add --no-cache ca-certificates
+
+COPY --from=builder /go/src/nubank/authorizer/authorize /usr/local/bin/
+
+CMD authorize
diff --git a/bin/yay b/bin/yay
index fac326f..6d4698e 100755
--- a/bin/yay
+++ b/bin/yay
@@ -1,7 +1,7 @@
-#!/usr/bin/env php 
+#!/usr/bin/env php
 <?php declare(strict_types=1);
 
-use Yay\{Engine};
+use Yay\{Engine, YayPreprocessorError};
 
 set_error_handler(function($errno, $errstr) {
     throw new Exception($errstr, $errno);
@@ -22,20 +22,62 @@ set_error_handler(function($errno, $errstr) {
     throw new Exception('Could not find autoload file. Check your composer installation.');
 })();
 
-
 try {
-    $file = $argv[1] ?? '';
 
-    $source = file_get_contents($file) ?: file_get_contents('php://stdin');
+$doc = <<<DOC
+YAY!
+
+Usage:
+  yay
+  yay <file>
+  yay --macros=<macros>
+  yay --macros=<macros> <file>
+  yay -h | --help
+  yay --version
+
+Options:
+  -h --help         Show this screen.
+  --version         Show version.
+  --macros=<macros> PHP glob pattern for macros to be loaded. Ex: my/macros/*.yay [default: '']
+
+Examples:
+
+``` 
+# Process file:
+yay input.php > output.php
+
+# Process file, preload project macros:
+> yay --macros="./project-macros/*.yay" input.php > output.php
+
+# Process stdin:
+> cat input.php | yay > output.php
+
+# Process stdin, preload project macros:
+> cat input.php | yay --macros="./project-macros/*.yay" > output.php
+```
+DOC;
+
+    $argv = Docopt::handle($doc, include __DIR__ . '/../meta.php');
+
+    $file = $argv['<file>'] ?? 'php://stdin';
+
+    $source = file_get_contents($file);
+
+    $engine = new Engine;
 
     gc_disable();
 
-    $expansion = (new Engine)->expand($source, $file);
+    foreach(glob((string) $argv['--macros']) as $f) $engine->expand(file_get_contents($f), $f);
+
+    $expansion = $engine->expand($source, $file);
 
     gc_enable();
 
     file_put_contents('php://stdout', $expansion);
 }
+catch (YayPreprocessorError $e) {
+    file_put_contents('php://stderr', $e . PHP_EOL);
+}
 catch (Exception $e) {
     file_put_contents('php://stderr', $e . PHP_EOL);
 }
diff --git a/composer.json b/composer.json
index bbe9631..0f416ea 100644
--- a/composer.json
+++ b/composer.json
@@ -18,7 +18,8 @@
         "php": "7.*",
         "ext-mbstring": "*",
         "ext-tokenizer": "*",
-        "nikic/php-parser": "^2.1|^3.0|^4.0"
+        "nikic/php-parser": "^2.1|^3.0|^4.0",
+        "docopt/docopt": "^1.0"
     },
     "autoload": {
         "files": [
diff --git a/meta.php b/meta.php
new file mode 100644
index 0000000..4fd01d3
--- /dev/null
+++ b/meta.php
@@ -0,0 +1,3 @@
+<?php return [
+    'version' => '0.7'
+];
diff --git a/src/Ast.php b/src/Ast.php
index 3fe5ee6..41de9b5 100644
--- a/src/Ast.php
+++ b/src/Ast.php
@@ -2,14 +2,12 @@
 
 namespace Yay;
 
-use
-    InvalidArgumentException,
-    ArrayIterator,
-    TypeError
-;
-
 class Ast implements Result {
 
+    const
+        NULL_LABEL = '_'
+    ;
+
     protected
         $label = '',
         $ast = []
@@ -21,12 +19,29 @@ class Ast implements Result {
 
     function __construct(string $label = '', $ast = []) {
         if ($ast instanceof self)
-            throw new InvalidArgumentException('Unmerged AST.');
+            throw new YayPreprocessorError('Unmerged AST.');
 
         $this->ast = $ast;
         $this->label = $label;
     }
 
+    function __set($path, $value) {
+        return $this->set($path, $value);
+    }
+
+    function set($strPath, $value) {
+        $keys = preg_split('/\s+/', $strPath);
+
+        if ([] === $keys) return;
+
+        $current = &$this->ast;
+        foreach ($keys as $key) {
+            if (!is_array($current)) $current = [];
+            $current = &$current[$key];
+        }
+        $current = $value;
+    }
+
     function __get($path) {
         return $this->get($path);
     }
@@ -68,7 +83,8 @@ function tokens() {
 
         array_walk_recursive(
             $exposed,
-            function($i) use(&$tokens){
+            function($i, $key) use(&$tokens){
+                if (0 === strpos((string) $key, self::NULL_LABEL)) return;
                 if($i instanceof Token) $tokens[] = $i;
                 elseif ($i instanceof self) $tokens = array_merge($tokens, $i->tokens());
             }
@@ -103,7 +119,7 @@ function array() {
     }
 
     function list() {
-        foreach (array_keys($this->array()) as $index) yield $index => $this->{"* {$index}"};
+        foreach (array_keys($this->array()) as $i) if($i !== self::NULL_LABEL) yield $i => $this->{"* {$i}"};
     }
 
     function flatten() : self {
@@ -113,8 +129,7 @@ function flatten() : self {
     function append(self $ast) : self {
         if ('' !== $ast->label) {
             if (isset($this->ast[$ast->label]))
-                throw new InvalidArgumentException(
-                    "Duplicated AST label '{$ast->label}'.");
+                throw new YayPreprocessorError("Duplicated AST label '{$ast->label}'.");
 
             $this->ast[$ast->label] = $ast->ast;
         }
@@ -130,7 +145,7 @@ function push(self $ast) : self {
     }
 
     function isEmpty() : bool {
-        return null === $this->ast || 0 === \count($this->ast);
+        return null === $this->ast || [] === $this->ast;
     }
 
     function as(string $label = '') : Result {
@@ -150,7 +165,7 @@ function withMeta(Map $meta) : Result {
     }
 
     function meta() : Map {
-        return $this->meta ?: Map::fromEmpty();
+        return $this->meta ?: $this->meta = Map::fromEmpty();
     }
 
 
@@ -189,6 +204,6 @@ private function getIn(array $array, array $keys, $default = null)
     }
 
     private function failCasting(string $type) {
-        throw new YayException(sprintf("Ast cannot be casted to '%s'", $type));
+        throw new YayPreprocessorError(sprintf("Ast cannot be casted to '%s'", $type));
     }
 }
diff --git a/src/Engine.php b/src/Engine.php
index bf4fbcd..b44a580 100644
--- a/src/Engine.php
+++ b/src/Engine.php
@@ -110,8 +110,6 @@ function(Ast $node) :string { return (string) $node->{'* tag'}->token(); },
                 $macro = new Macro($tags, $pattern, $compilerPass, $expansion);
 
                 $this->registerDirective($macro);
-
-                if ($macro->tags()->contains('global')) $this->globalDirectives[] = $macro;
             })
         ;
 
@@ -160,6 +158,8 @@ function registerDirective(Directive $directive) {
                 krsort($this->typeHitMap[$expected->type()]);
             }
         }
+
+        if ($directive->tags()->contains('global')) $this->globalDirectives[] = $directive;
     }
 
     function blueContext() : BlueContext {
@@ -175,28 +175,43 @@ function currentFileName() : string {
     }
 
     function expand(string $source, string $filename = '', int $gc = self::GC_ENGINE_ENABLED) : string {
-
         $this->filename = $filename;
 
         foreach ($this->globalDirectives as $d) $this->registerDirective($d);
 
         $ts = TokenStream::{$filename && self::GC_ENGINE_ENABLED === $gc ? 'fromSource' : 'FromSourceWithoutOpenTag'}($source);
 
-        ($this->expander)($ts);
-        $expansion = (string) $ts;
-
-        if (self::GC_ENGINE_ENABLED === $gc) {
-            // almost everything is local per file so state must be destroyed after expansion
-            // unless the flag ::GC_ENGINE_ENABLED forces a recycle during nested expansions
-            // global directives are allocated again later to give impression of persistence
-            // ::GC_ENGINE_DISABLED indicates the current pass is an internal Engine recursion
-            $this->cycle = new Cycle;
-            $this->literalHitMap= $this->typeHitMap = [];
-            $this->blueContext = new BlueContext;
-        }
-
-        $this->filename = '';
+        try {
+            ($this->expander)($ts);
 
-        return $expansion;
+            return (string) $ts;
+        }
+        catch(YayPreprocessorError $error) {
+            throw new class(
+                str_replace(' on line', sprintf(', in %s on line', $this->filename), $error->getMessage()),
+                $error->getCode(),
+                $error,
+                $this->filename ?: '-',
+                1
+            ) extends YayPreprocessorError {
+                function __construct($message = '', $code = 0, \Throwable $error = null, $file = '', $line = 0) {
+                    parent::__construct($message, $code, $error);
+                    $this->file = $file;
+                    $this->line = $line;
+                }
+            };
+        }
+        finally {
+            if (self::GC_ENGINE_ENABLED === $gc) {
+                // almost everything is local per file so state must be destroyed after expansion
+                // unless the flag ::GC_ENGINE_ENABLED forces a recycle during nested expansions
+                // global directives are allocated again later to give impression of persistence
+                // ::GC_ENGINE_DISABLED indicates the current pass is an internal Engine recursion
+                $this->cycle = new Cycle;
+                $this->literalHitMap= $this->typeHitMap = [];
+                $this->blueContext = new BlueContext;
+            }
+            $this->filename = '';
+        }
     }
 }
diff --git a/src/Error.php b/src/Error.php
index 8955e2a..dd567e2 100644
--- a/src/Error.php
+++ b/src/Error.php
@@ -78,8 +78,4 @@ function message() : string {
 
         return implode(PHP_EOL, $messages);
     }
-
-    function halt() {
-        throw new Halt($this->message());
-    }
 }
diff --git a/src/Expansion.php b/src/Expansion.php
index aad5b3b..fb55863 100644
--- a/src/Expansion.php
+++ b/src/Expansion.php
@@ -206,15 +206,8 @@ private function mutate(TokenStream $ts, Ast $context, Engine $engine) : TokenSt
                 consume($this->expanderExpansion())->onCommit(function(Ast $result) use ($states) {
                     $cg = $states->current();
 
-                    $expander = $result->{'* expander'};
-                    if (\count($result->{'args'}) === 0)
-                        $cg->this->fail(self::E_EMPTY_EXPANDER_SLICE, $expander->implode(), $expander->tokens()[0]->line());
+                    $mutation = $this->doExpanderCall($result, $cg);
 
-                    $expansion = TokenStream::fromSlice($result->{'args'});
-                    $mutation = $cg->this->mutate($expansion, $cg->context, $cg->engine);
-
-                    $expander = $cg->this->compileCallable('\Yay\Dsl\Expanders\\', $expander, self::E_BAD_EXPANDER);
-                    $mutation = $expander($mutation, $cg->engine);
                     $cg->ts->inject($mutation);
                 })
                 ,
@@ -230,19 +223,29 @@ private function mutate(TokenStream $ts, Ast $context, Engine $engine) : TokenSt
 
                     $context = $context->unwrap();
 
+                    if (! is_array($context))
+                        $this->fail(
+                            "Error unpacking a non unpackable Ast node on `$(%s%s... {` at line %d with context: %s\n\n%s",
+                            $result->{'* label _name'}->token(),
+                            $result->optional,
+                            $result->{'* label _name'}->token()->line(),
+                            json_encode([$context], self::PRETTY_PRINT),
+                            sprintf("Hint: use a non ellipsis expansion as in `$(%s %s {`", $result->{'* label _name'}->token(), $result->optional)
+                        );
+
                     $delimiters = $result->{'delimiters'};
 
                     // normalize associative arrays
                     if (array_values($context) !== $context) $context = [$context];
 
-                    foreach (array_reverse($context, true) as $i => $iterationContext) {
+                    foreach (array_reverse($context, true) as $i => $scope) {
                         if ($key = $result->{'key'}) {
-                            $iterationContext[(string) $result->{'key'}] = new Token(T_LNUMBER, (string) $i);
+                            $scope[(string) $result->{'key'}] = new Token(T_LNUMBER, (string) $i);
                         }
                         $expansion = TokenStream::fromSlice($result->{'expansion'});
                         $mutation = $cg->this->mutate(
                             $expansion,
-                            (new Ast('', $cg->context->unwrap() + $iterationContext)),
+                            (new Ast('', $cg->context->unwrap() + (is_array($scope) ? $scope : [$scope]))),
                             $cg->engine
                         );
                         if ($i !== count($context)-1) foreach ($delimiters as $d) $mutation->push($d);
@@ -297,14 +300,14 @@ private function mutate(TokenStream $ts, Ast $context, Engine $engine) : TokenSt
     }
 
     private function lookupAst(Ast $label, Ast $context, string $error) : Ast {
-        $symbol = $label->{'* name'}->token();
+        $symbol = $label->{'* _name'}->token();
         if (null === ($result = $context->get('* ' . $symbol))->unwrap()) {
             $this->fail(
                 $error,
-                $label->{'complex'} ? $label->{'* complex_name'}->implode() : $symbol,
+                $label->{'_complex'} ? $label->{'* _complex_name'}->implode() : $symbol,
                 $symbol->line(),
                 json_encode(
-                    $label->{'complex'}
+                    $label->{'_complex'}
                         ? array_values(array_filter($context->symbols(), 'is_string'))
                         : $context->symbols()
                     ,
@@ -317,11 +320,82 @@ private function lookupAst(Ast $label, Ast $context, string $error) : Ast {
     }
 
     private function lookupAstOptional(Ast $label, Ast $context) : Ast {
-        $result = $context->get('* ' . (string) $label->{'* name'}->token());
+        $result = $context->get('* ' . (string) $label->{'* _name'}->token());
 
         return $result;
     }
 
+    private function doExpanderCall(Ast $ast, $cg) : TokenStream {
+        $function = $cg->this->compileCallable('\Yay\Dsl\Expanders\\', $ast->{'* expander'}, self::E_BAD_EXPANDER);
+        $expander = new \ReflectionFunction($function);
+        $delayed = function($expander) { return $expander->invoke(); };
+        if ($expander->getParameters()) {
+            if (($class = $expander->getParameters()[0]->getClass()) && Ast::class === $class->getName()) {
+                $delayed = function($expander, $ast, $cg) { return $this->doAstExpanderCall($expander, $ast, $cg); };
+            } else {
+                $delayed = function($expander, $ast, $cg) { return $this->doTokenStreamExpanderCall($expander, $ast, $cg); };
+            }
+        }
+
+        $mutation = $delayed($expander, $ast, $cg);
+
+        if (! ($mutation instanceof TokenStream || $mutation instanceof Ast)) $this->fail(
+            'Expander call `%s(%s)` must return Ast or TokenStream, %s returned on line %d',
+            $expander->getName(),
+            implode(
+                ', ',
+                array_map(function($p){ return preg_replace('/Parameter #\d+ \[ |<.+> | \]/', '', $p); },
+                $expander->getParameters())
+            ),
+            gettype($mutation),
+            $ast->{'* expander'}->tokens()[0]->line()
+        );
+
+        if ($mutation instanceof Ast) $mutation = TokenStream::fromSlice($mutation->tokens());
+
+        return $mutation;
+    }
+
+    private function doTokenStreamExpanderCall(\ReflectionFunction $expander, Ast $expanderAst, $cg): TokenStream {
+        $ts = TokenStream::fromSlice(array_slice($expanderAst->{'* args'}->tokens(), 1, -1));
+
+        if ($ts->isEmpty()) $this->fail(
+            'TokenStream expander call without tokens `%s` as function %s(%s) on line %d',
+            $expanderAst->implode(),
+            $expander->getName(),
+            implode(
+                ', ',
+                array_map(function($p){ return preg_replace('/Parameter #\d+ \[ |<.+> | \]/', '', $p); },
+                $expander->getParameters())
+            ),
+            $expanderAst->{'* expander'}->tokens()[0]->line()
+        );
+
+        return $expander->invoke($cg->this->mutate($ts, $cg->context, $cg->engine), $cg->engine);
+    }
+
+    private function doAstExpanderCall(\ReflectionFunction $expander, Ast $expanderAst, $cg) {
+        $arg = null;
+        if ($expanderAst->{'args leaf_arg'}) {
+            $arg = $this->lookupAst($expanderAst->{'* args leaf_arg label'}, $cg->context, self::E_UNDEFINED_EXPANSION);
+        }
+        else if($expanderAst->{'args expander_call'}) {
+            $arg = $this->doAstExpanderCall(
+                new \ReflectionFunction(
+                    $cg->this->compileCallable(
+                        '\Yay\Dsl\Expanders\\',
+                        $expanderAst->{'* args expander_call expander'},
+                        self::E_BAD_EXPANDER
+                    )
+                ),
+                $expanderAst->{'* args expander_call'},
+                $cg
+            );
+        }
+
+        return $expander->invoke($arg, $cg->engine);
+    }
+
     private function conditionalLabelExpansion() : Parser {
         return
             sigil
@@ -352,8 +426,37 @@ private function expanderExpansion() : Parser {
             (
                 ns()->as('expander')
                 ,
-                either(parentheses(), braces())->as('args')
+                either
+                (
+                    chain(token('('), optional($this->expanderAstExpansion()), token(')')) // recursion !!!
+                    ,
+                    chain(token('('), $this->labelExpansion()->as('leaf_arg'), token(')'))
+                    ,
+                    chain(token('('), optional(layer()->as('layer_arg')), token(')'))
+                    ,
+                    chain(token('{'), optional(layer()->as('layer_arg')), token('}'))
+                )
+                ->as('args')
+            )
+            ->as('expander_call')
+        ;
+    }
+
+    private function expanderAstExpansion() : Parser {
+        return
+            $expander = expander_sigil
+            (
+                ns()->as('expander')
+                ,
+                either
+                (
+                    chain(token('('), pointer($expander), token(')')) // recursion !!!
+                    ,
+                    chain(token('('), $this->labelExpansion()->as('leaf_arg'), token(')'))
+                )
+                ->as('args')
             )
+            ->as('expander_call')
         ;
     }
 
diff --git a/src/ExpressionParser.php b/src/ExpressionParser.php
index 03e6e27..7f6a657 100644
--- a/src/ExpressionParser.php
+++ b/src/ExpressionParser.php
@@ -75,7 +75,7 @@ private function rebuildParser() : Parser
         $arguments = pointer($arguments)->as('arguments_pointer');
         // }
 
-        if (null === $this->stack[0]) {
+        if (null === $this->stack) {
             $this->addOperator(self::ARITY_UNARY|self::ASSOC_RIGHT, token(T_INCLUDE), token(T_INCLUDE_ONCE), token(T_REQUIRE), token(T_REQUIRE_ONCE));
             $this->addOperator(self::ARITY_BINARY|self::ASSOC_LEFT, chain(token(T_LOGICAL_OR), optional(indentation())));
             $this->addOperator(self::ARITY_BINARY|self::ASSOC_LEFT, chain(token(T_LOGICAL_XOR), optional(indentation())));
@@ -406,7 +406,7 @@ private function inferPositionalBehavior(int $flags) : int
     {
         foreach ([self::POS_PREFIX, self::POS_INFIX, self::POS_SUFFIX] as $p) if(($flags & $p) === $flags) return $p;
 
-        throw new \Exception('Could not infer operator positional behaviour.');
+        throw new YayPreprocessorError('Could not infer operator positional behaviour.');
     }
 
     /**
@@ -414,7 +414,7 @@ private function inferPositionalBehavior(int $flags) : int
      */
     private function validateBitTable(int $flags, string $message)
     {
-        if (! ($flags && !($flags & ($flags-1)))) throw new \Exception($message);
+        if (! ($flags && !($flags & ($flags-1)))) throw new YayPreprocessorError($message);
     }
 
     private function inferPrecedence() : int
diff --git a/src/Halt.php b/src/Halt.php
deleted file mode 100644
index e9804cf..0000000
--- a/src/Halt.php
+++ /dev/null
@@ -1,5 +0,0 @@
-<?php declare(strict_types=1);
-
-namespace Yay;
-
-class Halt extends YayParseError {}
diff --git a/src/Macro.php b/src/Macro.php
index be06b8b..16314c9 100644
--- a/src/Macro.php
+++ b/src/Macro.php
@@ -26,7 +26,7 @@ function __construct(Map $tags, PatternInterface $pattern, CompilerPass $compile
         $this->compilerPass = $compilerPass;
         $this->expansion = $expansion;
 
-        $this->enableParserTracer = $this->tags->contains('enable_parser_tarcer');
+        $this->enableParserTracer = $this->tags->contains('enable_parser_tracer');
         $this->isTerminal = !$this->expansion->isRecursive();
     }
 
diff --git a/src/MacroMember.php b/src/MacroMember.php
index 21553d8..8d96aef 100644
--- a/src/MacroMember.php
+++ b/src/MacroMember.php
@@ -13,7 +13,7 @@ abstract class MacroMember {
     ;
 
     protected function fail(string $error, ...$args) {
-        throw new YayParseError(sprintf($error, ...$args));
+        throw new YayPreprocessorError(sprintf($error, ...$args));
     }
 
     protected function compileCallable(string $namespace, Ast $type, string $error): callable {
diff --git a/src/Parser.php b/src/Parser.php
index 611559d..739edf1 100644
--- a/src/Parser.php
+++ b/src/Parser.php
@@ -2,10 +2,6 @@
 
 namespace Yay;
 
-use
-    InvalidArgumentException
-;
-
 use Yay\ParserTracer\{ParserTracer, NullParserTracer};
 
 /**
@@ -79,7 +75,7 @@ function parse(TokenStream $ts) /*: Result|null*/
                 self::$tracer->trace($index, 'error');
             }
         }
-        catch(Halt $e) {
+        catch(YayPreprocessorError $e) {
             $ts->jump($index);
             self::$tracer->trace($index, 'error');
 
@@ -109,7 +105,7 @@ function as(string $label) : self
     {
         if ('' !== (string) $label) {
             if(false !== strpos($label, ' '))
-                throw new InvalidArgumentException(
+                throw new YayPreprocessorError(
                     "Parser label cannot contain spaces, '{$label}' given.");
 
             $this->label = $label;
diff --git a/src/Pattern.php b/src/Pattern.php
index 4a2ef28..73101ac 100644
--- a/src/Pattern.php
+++ b/src/Pattern.php
@@ -255,6 +255,44 @@ private function compileAlias(Ast $alias) : string {
         return $identifier;
     }
 
+    protected function compileArray(Ast $array) : array {
+        $compiled = [];
+        foreach ($array->{'* values'}->list() as $valueNode) {
+            $key = count($compiled);
+            $value = $valueNode->{'* value'};
+
+            if ($valueNode->{'key_value_pair'}) {
+                $value = $valueNode->{'* key_value_pair value'};
+                $type = key($valueNode->{'* key_value_pair key'}->array());
+                $key = $valueNode->{"* key_value_pair key {$type}"};
+                switch ($type) {
+                  case 'string':
+                      $key =  trim((string) $key->token(), '"\'');
+                      break;
+                  case 'int':
+                      $key =  (int) $key->token()->value();
+                }
+            }
+
+            $type = key($value->array());
+            $value = $value->{"* {$type}"};
+            switch ($type) {
+              case 'string':
+                  $value =  trim((string) $value->token(), '"\'');
+                  break;
+              case 'int':
+                  $value =  (int) $value->token()->value();
+                  break;
+              case 'array':
+                  $value = $this->compileArray($value);
+            }
+
+            $compiled[$key] = $value;
+        }
+
+        return $compiled;
+    }
+
     protected function compileParser(Ast $ast) : Parser {
         $parser = $this->compileCallable('\Yay\\', $ast->{'* type'}, self::E_BAD_PARSER_NAME);
         $args = $ast->{'* args'}->isEmpty() ? [] : $this->compileParserArgs($ast->{'* args'});
@@ -291,6 +329,9 @@ protected function compileParserArgs(Ast $args) : array {
                 case 'string':
                     $compiled[] = trim((string) $arg->token(), '"\'');
                     break;
+                case 'array':
+                    $compiled[] = $this->compileArray($arg);
+                    break;
                 case 'function': // function(...){...}
                     $compiled[] = new AnonymousFunction($arg);
                     break;
diff --git a/src/StreamWrapper.php b/src/StreamWrapper.php
deleted file mode 100644
index 1d32fc3..0000000
--- a/src/StreamWrapper.php
+++ /dev/null
@@ -1,151 +0,0 @@
-<?php declare(strict_types=1);
-
-namespace Yay;
-
-use function yay_parse;
-
-use
-    SplFileObject,
-    SplFileInfo
-;
-
-final class StreamWrapper {
-    const
-        SCHEME = 'yay',
-        STAT_MTIME_NUMERIC_OFFSET = 9,
-        STAT_MTIME_ASSOC_OFFSET = 'mtime'
-    ;
-
-    protected static
-        $registered = false,
-        $engine
-    ;
-
-    protected
-        $resource
-    ;
-
-    static function register(Engine $engine)
-    {
-        if (true === self::$registered) return;
-
-        if (@stream_wrapper_register(self::SCHEME, __CLASS__) === false)
-            throw new YayException(
-                'A handler has already been registered for the ' .
-                self::SCHEME . ' protocol.'
-            );
-
-        self::$engine = $engine;
-        self::$registered = true;
-    }
-
-    static function unregister()
-    {
-        if (!self::$registered) {
-            if (in_array(self::SCHEME, stream_get_wrappers()))
-                throw new YayException(
-                    'The URL wrapper for the protocol ' . self::SCHEME .
-                    ' was not registered with this version of YAY.'
-                );
-
-            return;
-        }
-
-        if (!@stream_wrapper_unregister(self::SCHEME))
-            throw new YayException(
-                'Failed to unregister the URL wrapper for the ' . self::SCHEME .
-                ' protocol.'
-            );
-
-        self::$engine = null;
-        self::$registered = false;
-    }
-
-    function stream_open(string $path, string $mode, int $flags, &$opened_path) : bool
-    {
-        $path = preg_replace('#^' . self::SCHEME . '://#', '', $path);
-
-        if (STREAM_USE_PATH & $flags && $path[0] !== '/')
-            $path = dirname(debug_backtrace()[0]['file']) . '/' . $path;
-
-        $fileMeta = new SplFileInfo($path);
-
-        if (! $fileMeta->isReadable()) return false;
-
-        $opened_path = $path;
-
-        $source = self::$engine->expand(file_get_contents($fileMeta->getRealPath()), $fileMeta->getRealPath());
-
-        $this->resource = fopen('php://memory', 'rb+');
-        fwrite($this->resource, $source);
-        rewind($this->resource);
-
-        return true;
-    }
-
-    function stream_close() {
-        fclose($this->resource);
-    }
-
-    function stream_read($length) : string {
-        $source =
-            ! feof($this->resource)
-                ? fread($this->resource, $length)
-                : ''
-        ;
-
-        return $source;
-    }
-
-    function stream_eof() : bool { return feof($this->resource); }
-
-    function stream_stat() : array
-    {
-        $stat = fstat($this->resource);
-        if ($stat) {
-            $stat[self::STAT_MTIME_ASSOC_OFFSET]++;
-            $stat[self::STAT_MTIME_NUMERIC_OFFSET]++;
-        }
-        return $stat;
-    }
-
-    function url_stat() { $this->notImplemented(__FUNCTION__); }
-
-    function stream_write() { $this->notImplemented(__FUNCTION__); }
-
-    function stream_truncate() { $this->notImplemented(__FUNCTION__); }
-
-    function stream_metadata() { $this->notImplemented(__FUNCTION__); }
-
-    function stream_tell() { $this->notImplemented(__FUNCTION__); }
-
-    function stream_seek() { $this->notImplemented(__FUNCTION__); }
-
-    function stream_flush() { $this->notImplemented(__FUNCTION__); }
-
-    function stream_cast() { $this->notImplemented(__FUNCTION__); }
-
-    function stream_lock() { $this->notImplemented(__FUNCTION__); }
-
-    function stream_set_option() { $this->notImplemented(__FUNCTION__); }
-
-    function unlink() { $this->notImplemented(__FUNCTION__); }
-
-    function rename() { $this->notImplemented(__FUNCTION__); }
-
-    function mkdir() { $this->notImplemented(__FUNCTION__); }
-
-    function rmdir() { $this->notImplemented(__FUNCTION__); }
-
-    function dir_opendir() { $this->notImplemented(__FUNCTION__); }
-
-    function dir_readdir() { $this->notImplemented(__FUNCTION__); }
-
-    function dir_rewinddir() { $this->notImplemented(__FUNCTION__); }
-
-    function dir_closedir() { $this->notImplemented(__FUNCTION__); }
-
-    private function notImplemented(string $from) {
-        throw new YayException(__CLASS__ . "->{$from} is not implemented.");
-    }
-}
diff --git a/src/TokenStream.php b/src/TokenStream.php
index 3ecebc0..068b79f 100644
--- a/src/TokenStream.php
+++ b/src/TokenStream.php
@@ -2,10 +2,6 @@
 
 namespace Yay;
 
-use
-    InvalidArgumentException
-;
-
 class TokenStream {
 
     protected
diff --git a/src/YayException.php b/src/YayException.php
deleted file mode 100644
index f8d5360..0000000
--- a/src/YayException.php
+++ /dev/null
@@ -1,5 +0,0 @@
-<?php declare(strict_types=1);
-
-namespace Yay;
-
-class YayException extends \Exception {}
diff --git a/src/YayParseError.php b/src/YayParseError.php
deleted file mode 100644
index b9a009f..0000000
--- a/src/YayParseError.php
+++ /dev/null
@@ -1,5 +0,0 @@
-<?php declare(strict_types=1);
-
-namespace Yay;
-
-class YayParseError extends \ParseError {}
diff --git a/src/YayPreprocessorError.php b/src/YayPreprocessorError.php
new file mode 100644
index 0000000..776cec6
--- /dev/null
+++ b/src/YayPreprocessorError.php
@@ -0,0 +1,5 @@
+<?php declare(strict_types=1);
+
+namespace Yay;
+
+class YayPreprocessorError extends \ParseError {}
diff --git a/src/expanders.php b/src/expanders.php
index d0319cb..54f080a 100644
--- a/src/expanders.php
+++ b/src/expanders.php
@@ -2,7 +2,7 @@
 
 namespace Yay\DSL\Expanders;
 
-use Yay\{Engine, Token, TokenStream, Ast, YayException, Cycle, Parser, Context};
+use Yay\{Engine, Token, TokenStream, Ast, Cycle, Parser, Context, YayPreprocessorError};
 use function Yay\{
     token, rtoken, identifier, chain, either, any, parentheses, braces, traverse, midrule, buffer
 };
@@ -38,7 +38,7 @@ function concat(TokenStream $ts) : TokenStream {
     while($t = $ts->current()) {
         $str = (string) $t;
         if (! preg_match('/^\w+$/', $str))
-            throw new YayException(
+            throw new YayPreprocessorError(
                 "Only valid identifiers are mergeable, '{$t->dump()}' given.");
 
         $buffer .= $str;
diff --git a/src/parsers.php b/src/parsers.php
index 7c556cf..bccaa06 100644
--- a/src/parsers.php
+++ b/src/parsers.php
@@ -2,10 +2,6 @@
 
 namespace Yay;
 
-use
-    InvalidArgumentException
-;
-
 function token($type, $value = null) : Parser
 {
     $token = $type instanceof Token ? $type : new Token($type, $value);
@@ -68,7 +64,7 @@ function isFallible() : bool
 function rtoken(string $regexp) : Parser
 {
     if (false === preg_match($regexp, ''))
-        throw new InvalidArgumentException('Invalid regexp at ' . __FUNCTION__);
+        throw new YayPreprocessorError('Invalid regexp at ' . __FUNCTION__);
 
     return new class(__FUNCTION__, $regexp) extends Parser
     {
@@ -267,7 +263,7 @@ function isFallible() : bool
 function repeat(Parser $parser) : Parser
 {
     if (! $parser->isFallible())
-        throw new InvalidArgumentException(
+        throw new YayPreprocessorError(
             'Infinite loop at ' . __FUNCTION__ . '('. $parser . '(*))');
 
     return new class(__FUNCTION__, $parser) extends Parser
@@ -534,7 +530,7 @@ function either(Parser ...$routes) : Parser
     foreach ($routes as $i => $route)
         if ($route !== $last && ! $route->isFallible()) {
             $parser = $routes[++$i];
-            throw new InvalidArgumentException(
+            throw new YayPreprocessorError(
                 "Dead {$parser}() parser at " . __FUNCTION__ . "(...[{$i}])");
         }
 
@@ -601,7 +597,7 @@ function optimize() : Parser
                     foreach ($parser->expected()->all() as $prefixToken)
                         $jumptable[$prefixToken->type()][] = $parser->optimize();
                 else
-                    throw new \Exception("Cannot optimize {$this} parser stack at {$parser}");
+                    throw new YayPreprocessorError("Cannot optimize {$this} parser stack at {$parser}");
 
             foreach ($jumptable as $prefix => $possibleRoutes) {
                 if (count($possibleRoutes) > 1) $jumptable[$prefix] = either(...$possibleRoutes);
@@ -719,7 +715,7 @@ function isFallible() : bool
 function optional(Parser $parser, $default = []) : Parser
 {
     if ($default instanceof Parser)
-        throw new InvalidArgumentException("optional() default value must not be <Parser>");
+        throw new YayPreprocessorError("optional() default value must not be <Parser>");
 
     return new class(__FUNCTION__, $parser, $default) extends Parser
     {
@@ -751,7 +747,7 @@ protected function parser(TokenStream $ts, Parser $parser) : Ast
         {
             $result = $parser->withErrorLevel(Error::ENABLED)->parse($ts);
 
-            if ($result instanceof Error) $result->halt();
+            if ($result instanceof Error) throw new YayPreprocessorError($result->message());
 
             return $result->as($this->label);
         }
@@ -815,7 +811,7 @@ function ns() : Parser
 function ls(Parser $parser, Parser $delimiter, int $flags = LS_DISCARD_DELIMITER) : Parser
 {
     if (! $parser->isFallible())
-        throw new InvalidArgumentException(
+        throw new YayPreprocessorError(
             'Infinite loop at ' . __FUNCTION__ . '('. $parser . '(*))');
 
     return new class(__FUNCTION__, $parser, $delimiter, $flags) extends Parser
@@ -866,7 +862,7 @@ function isFallible() : bool
 function lst(Parser $parser, Parser $delimiter, int $flags = LS_DISCARD_DELIMITER) : Parser
 {
     if (! $parser->isFallible())
-        throw new InvalidArgumentException(
+        throw new YayPreprocessorError(
             'Infinite loop at ' . __FUNCTION__ . '('. $parser . '(*))');
 
     return new class(__FUNCTION__, $parser, $delimiter, $flags) extends Parser
@@ -962,7 +958,7 @@ function optimize() : Parser
         private function preventCircularPointerDereference()
         {
             if (pointer::class === $this->type && $this->stack[0] === $this->stack[0]()->stack[0])
-                throw new \Exception("Circular pointer dereference at {$this}.");
+                throw new YayPreprocessorError("Circular pointer dereference at {$this}.");
         }
     };
 }
@@ -1060,7 +1056,7 @@ function midrule(callable $midrule, bool $isFallible = true, Expected $expected
     {
         function parser(TokenStream $ts) /*: Result|null*/
         {
-            $result = $this->stack[0]($ts);
+            $result = $this->stack[0]($ts, $this->label);
 
             if ($result instanceof Ast) $result->as($this->label);
 
diff --git a/src/parsers_internal.php b/src/parsers_internal.php
index a1172fe..843a8ee 100644
--- a/src/parsers_internal.php
+++ b/src/parsers_internal.php
@@ -75,6 +75,43 @@ function token_constant() : Parser {
     return rtoken('/^T_\w+$/')->as('token_constant');
 }
 
+function array_arg(): Parser {
+    $string = string()->as('string');
+    $int = token(T_LNUMBER)->as('int');
+    return $array =
+        chain(
+            token('[')
+            ,
+            commit(
+                optional(
+                    lst(
+                        either(
+                            chain(
+                                either($int, $string)->as('key'),
+                                token(T_DOUBLE_ARROW),
+                                either(
+                                    chain($int)->as('value'),
+                                    chain($string)->as('value'),
+                                    chain(pointer($array))->as('value')
+                                )
+                            )
+                            ->as('key_value_pair')
+                            ,
+                            chain($int)->as('value'),
+                            chain($string)->as('value'),
+                            chain(pointer($array))->as('value')
+                        ),
+                        token(',')
+                    )
+                    ->as('values')
+                )
+            )
+            ,
+            token(']')
+        )
+        ->as('array');
+}
+
 function parsec() : Parser {
     return
         $parser =
@@ -114,6 +151,8 @@ function parsec() : Parser {
                             sigil(token(T_STRING, 'this'))->as('this')
                             ,
                             label()->as('literal')
+                            ,
+                            array_arg()->as('array')
                         )
                         ,
                         token(',')
@@ -150,10 +189,10 @@ function label_or_array_access() : Parser {
             // becomes  a single Ast path string like `T_STRING(foo bar baz)`
             $ast->__construct(
                 $ast->label(),
-                [
-                    'name' => new Token(T_STRING, str_replace(['[', ']'], [' ', ''], $ast->implode()), $ast->tokens()[0]->line()),
-                    'complex_name' => new Token(T_STRING, $ast->implode(), $ast->tokens()[0]->line()),
-                    'complex' => (bool) $ast->complex,
+                $ast->unwrap() + [
+                    '_name' => new Token(T_STRING, str_replace(['[', ']'], [' ', ''], $ast->implode()), $ast->tokens()[0]->line()),
+                    '_complex_name' => new Token(T_STRING, $ast->implode(), $ast->tokens()[0]->line()),
+                    '_complex' => (bool) $ast->complex,
                 ]
             );
         })
diff --git a/tests/AstTest.php b/tests/AstTest.php
index e6ec81b..0c8fa9a 100644
--- a/tests/AstTest.php
+++ b/tests/AstTest.php
@@ -45,7 +45,7 @@ function providerForTestMapAstCastOnFailure() {
      * @dataProvider providerForTestMapAstCastOnFailure
      */
     function testMapAstCastOnFailure(string $path, string $castMethod, string $typeName) {
-        $this->expectException(YayException::class);
+        $this->expectException(YayPreprocessorError::class);
         $this->expectExceptionMessageRegExp("/^Ast cannot be casted to '{$typeName}'$/");
         $ast = new Ast('', ['defined' => true]);
         var_dump($ast->{$path}->$castMethod());
@@ -105,4 +105,47 @@ function testAstFlattenning() {
 
         $this->assertEquals([$token1, $token2], $flattened->array());
     }
+
+    function testAstSet() {
+        $ast = new Ast('label', [
+            'deep' => [
+                'token' => new Token(T_STRING, 'foo'),
+                'deeper' => [
+                    'tokens' => [0 => new Token(T_STRING, 'bar'), 1 => new Token(T_STRING, 'baz')],
+                ],
+            ],
+        ]);
+
+        $ast->set('deep token', $patchedFooToken = new Token(T_STRING, 'patched_foo'));
+
+        $ast->{'deep deeper tokens 0'} = $patchedBarToken = new Token(T_STRING, 'patched_bar');
+        $ast->{'deep deeper tokens 1'} = $patchedBazToken = new Token(T_STRING, 'patched_baz');
+
+        $expected = [
+            'deep' => [
+                'token' => $patchedFooToken,
+                'deeper' => [
+                    'tokens' => [0 => $patchedBarToken, 1 => $patchedBazToken],
+                ],
+            ],
+        ];
+
+        $this->assertSame($expected, $ast->unwrap());
+        $this->assertSame($expected, $ast->array());
+    }
+
+    function testAstHiddenNodes() {
+        $exposed = new Token(T_STRING, 'exposed');
+        $hidden = new Token(T_STRING, '_hidden');
+        $ast = new Ast('', [
+            'exposed' => $exposed,
+            '_hidden' => $hidden,
+            'deep' => [
+                'exposed' => $exposed,
+                '_hidden' => $hidden,
+            ]
+        ]);
+        $this->assertSame([$exposed, $exposed], $ast->tokens());
+        $this->assertSame('exposed,exposed', $ast->implode(','));
+    }
 }
diff --git a/tests/MacroScopeTest.php b/tests/MacroScopeTest.php
index 369b3be..1a67ac5 100644
--- a/tests/MacroScopeTest.php
+++ b/tests/MacroScopeTest.php
@@ -8,25 +8,16 @@
 class MacroScopeTest extends \PHPUnit\Framework\TestCase {
 
     const
-        FIXTURES_DIR = 'fixtures/scope',
-        ABSOLUTE_FIXTURES_DIR = __DIR__ . '/' . self::FIXTURES_DIR
+        ABSOLUTE_FIXTURES_DIR = __DIR__ . '/fixtures/scope'
     ;
 
-    function setUp() {
-        StreamWrapper::register(new Engine);
-    }
-
     function testGlobalMacro() {
-        include 'yay://' . self::ABSOLUTE_FIXTURES_DIR . '/macros.php';
-        $result = include 'yay://' . self::ABSOLUTE_FIXTURES_DIR . '/test_global.php';
-        $this->assertTrue($result);
-    }
+        $engine = new Engine;
 
-    function testLocalMacro() {
-        include 'yay://' . self::ABSOLUTE_FIXTURES_DIR . '/macros.php';
-        $result = include 'yay://' . self::ABSOLUTE_FIXTURES_DIR . '/test_local.php';
-        $this->assertEquals('LOCAL_MACRO', $result);
-    }
+        $source = str_replace('<?php', '', $engine->expand(file_get_contents(self::ABSOLUTE_FIXTURES_DIR . '/macros.php')));
+        $this->assertSame([true, true], eval($source));
 
-    function tearDown() { StreamWrapper::unregister(); }
+        $source = str_replace('<?php', '', $engine->expand(file_get_contents(self::ABSOLUTE_FIXTURES_DIR . '/run.php')));
+        $this->assertSame([true, 'LOCAL_MACRO'], eval($source));
+    }
 }
diff --git a/tests/ParserTest.php b/tests/ParserTest.php
index a19375d..d2029e0 100644
--- a/tests/ParserTest.php
+++ b/tests/ParserTest.php
@@ -18,7 +18,7 @@ function tearDown()
     }
 
     protected function parseHalt(TokenStream $ts, Parser $parser, $msg) {
-        $this->expectException(Halt::class);
+        $this->expectException(YayPreprocessorError::class);
         $this->expectExceptionMessage(implode(PHP_EOL, (array) $msg));
 
         $current = $ts->current();
@@ -32,7 +32,7 @@ function($commit) use($parser) {
             ->withErrorLevel(Error::ENABLED)
             ->parse($ts);
         }
-        catch (Halt $e) {
+        catch (YayPreprocessorError $e) {
             $this->assertSame($current, $ts->current(), 'Failed to backtrack.');
 
             throw $e;
@@ -379,7 +379,7 @@ function testChainOnEnd() {
     }
 
     /**
-     * @expectedException \InvalidArgumentException
+     * @expectedException \Yay\YayPreprocessorError
      * @expectedExceptionMessage Dead Yay\token() parser at Yay\either(...[2])
      */
     function testEitherDeadParserDetection() {
diff --git a/tests/SpecsTest.php b/tests/SpecsTest.php
index 8b306f9..3597132 100644
--- a/tests/SpecsTest.php
+++ b/tests/SpecsTest.php
@@ -112,9 +112,11 @@ function run() {
                     $stmts = $parser->parse($this->out);
                     $this->out = $prettyPrinter->prettyPrintFile($stmts) . PHP_EOL . PHP_EOL . '?>';
                 }
-            } catch(YayParseError $e) {
+            } catch(YayPreprocessorError $e) {
                 $this->out = $e->getMessage();
                 // $this->out = (string) $e;
+            } catch(YayRuntimeException $e) {
+                $this->out = $e->getMessage();
             } catch(\PhpParser\Error $e){
                 $this->out = 'PHP ' . $e->getMessage();
                 // $this->out = (string) $e;
diff --git a/tests/StreamWrapperTest.php b/tests/StreamWrapperTest.php
deleted file mode 100644
index 792e7ae..0000000
--- a/tests/StreamWrapperTest.php
+++ /dev/null
@@ -1,54 +0,0 @@
-<?php declare(strict_types=1);
-
-namespace Yay;
-
-/**
- * @group large
- */
-class StreamWrapperTest extends \PHPUnit\Framework\TestCase {
-
-    const
-        FIXTURES_DIR = 'fixtures/wrapper',
-        ABSOLUTE_FIXTURES_DIR = __DIR__ . '/' . self::FIXTURES_DIR
-    ;
-
-    function setUp() {
-        StreamWrapper::register(new Engine);
-    }
-
-    function syntaxErrorProvider() {
-
-        $fixtures = [
-            ['/syntax_error.php', "syntax error, unexpected '}'"],
-            ['/preprocessor_error.php', "Undefined token type 'T_HAKUNAMATATA'"]
-        ];
-
-        foreach ($fixtures as list($file, $message)) {
-            yield [self::FIXTURES_DIR . $file, $message];
-            yield [self::ABSOLUTE_FIXTURES_DIR . $file, $message];
-        }
-    }
-
-    /**
-     * @dataProvider syntaxErrorProvider
-     */
-    function testStreamWrapperOnSyntaxError(string $file, string $error) {
-        $this->expectException(\ParseError::class);
-        $this->expectExceptionMessage($error);
-        include 'yay://' . $file;
-    }
-
-    function testStreamWrapperInclusionRelative() {
-        include 'yay://' . self::FIXTURES_DIR . '/type_alias.php';
-        $result = \Yay\Fixtures\Wrapper\test_type_alias(__FILE__);
-        $this->assertEquals('pass', $result);
-    }
-
-    function testStreamWrapperInclusionAbsolute() {
-        include 'yay://' . self::ABSOLUTE_FIXTURES_DIR . '/type_alias_absolute.php';
-        $result = \Yay\Fixtures\Wrapper\test_type_alias_absolute(__FILE__);
-        $this->assertEquals('pass', $result);
-    }
-
-   function tearDown() { StreamWrapper::unregister(); }
-}
diff --git a/tests/fixtures/expanders.php b/tests/fixtures/expanders.php
index a500e6d..b80c52c 100644
--- a/tests/fixtures/expanders.php
+++ b/tests/fixtures/expanders.php
@@ -2,14 +2,48 @@
 
 use Yay\{Token, TokenStream};
 
-function my_hello_expander(TokenStream $ts) : TokenStream {
+function my_hello_tokenstream_expander(TokenStream $ts) : TokenStream {
     $str = str_replace("'", "\'", (string) $ts);
 
     return
         TokenStream::fromSequence(
             new Token(
-                T_CONSTANT_ENCAPSED_STRING, "'Hello, {$str}'", $ts->first()->line()
+                T_CONSTANT_ENCAPSED_STRING, "'Hello, {$str}. From TokenStream.'", $ts->first()->line()
             )
         )
     ;
 }
+
+function my_cheers_tokenstream_expander(TokenStream $ts) : TokenStream {
+    $str = str_replace("'", "", (string) $ts);
+
+    return
+        TokenStream::fromSequence(
+            new Token(
+                T_CONSTANT_ENCAPSED_STRING, "'{$str} Cheers!'", $ts->first()->line()
+            )
+        )
+    ;
+}
+
+function my_hello_ast_expander(\Yay\Ast $ast) : \Yay\Ast {
+    return new \Yay\Ast($ast->label(), new Token(
+        T_CONSTANT_ENCAPSED_STRING, "'Hello, {$ast->token()}. From Ast.'", $ast->token()->line()
+    ));
+}
+
+function my_cheers_ast_expander(\Yay\Ast $ast) : \Yay\Ast {
+    $str = str_replace("'", "", (string) $ast->token());
+
+    return new \Yay\Ast($ast->label(), new Token(
+        T_CONSTANT_ENCAPSED_STRING, "'{$str} Cheers!'", $ast->token()->line()
+    ));
+}
+
+function my_foo_expander(\Yay\Ast $ast) {
+    return TokenStream::fromSourceWithoutOpenTag(sprintf("'called %s(%s)'", __FUNCTION__, $ast->implode()));
+}
+
+function my_bar_expander(\Yay\Ast $ast) {
+    return TokenStream::fromSourceWithoutOpenTag(sprintf("'called %s(%s)'", __FUNCTION__, $ast->implode()));
+}
diff --git a/tests/fixtures/parsers.php b/tests/fixtures/parsers.php
index 1a7d71d..297a87b 100644
--- a/tests/fixtures/parsers.php
+++ b/tests/fixtures/parsers.php
@@ -1,8 +1,17 @@
 <?php namespace Yay\tests\fixtures\parsers;
 
-use Yay\{Parser};
-use function Yay\{token};
+use Yay\{Parser, Ast, Token};
+use function Yay\{token, midrule};
 
 function my_custom_parser() : Parser {
 	return token(T_STRING);
 }
+
+function var_dump_args_parser() : Parser {
+	ob_start();
+	var_dump(...func_get_args());
+	$dumped = ob_get_clean();
+	return midrule(function($_, $label) use($dumped) : Ast {
+		return new Ast('var_dump', new Token(T_CONSTANT_ENCAPSED_STRING, "/*\n{$label}: {$dumped}*/"));
+	});
+}
diff --git a/tests/fixtures/scope/macros.php b/tests/fixtures/scope/macros.php
index 06e6a19..16afe79 100644
--- a/tests/fixtures/scope/macros.php
+++ b/tests/fixtures/scope/macros.php
@@ -3,3 +3,5 @@
 $(macro :global) { 'GLOBAL_MACRO' } >> { true }
 
 $(macro) { 'LOCAL_MACRO' } >> { true }
+
+return ['GLOBAL_MACRO', 'LOCAL_MACRO'];
diff --git a/tests/fixtures/scope/run.php b/tests/fixtures/scope/run.php
new file mode 100644
index 0000000..2c60cb2
--- /dev/null
+++ b/tests/fixtures/scope/run.php
@@ -0,0 +1,3 @@
+<?php
+
+return ['GLOBAL_MACRO', 'LOCAL_MACRO'];
diff --git a/tests/fixtures/scope/test_global.php b/tests/fixtures/scope/test_global.php
deleted file mode 100644
index a70fa4a..0000000
--- a/tests/fixtures/scope/test_global.php
+++ /dev/null
@@ -1,3 +0,0 @@
-<?php
-
-return 'GLOBAL_MACRO';
diff --git a/tests/fixtures/scope/test_local.php b/tests/fixtures/scope/test_local.php
deleted file mode 100644
index a0c43c8..0000000
--- a/tests/fixtures/scope/test_local.php
+++ /dev/null
@@ -1,3 +0,0 @@
-<?php
-
-return 'LOCAL_MACRO';
diff --git a/tests/fixtures/wrapper/preprocessor_error.php b/tests/fixtures/wrapper/preprocessor_error.php
deleted file mode 100644
index 421d18a..0000000
--- a/tests/fixtures/wrapper/preprocessor_error.php
+++ /dev/null
@@ -1,3 +0,0 @@
-<?php
-
-$(macro) { $(T_HAKUNAMATATA as foo) } >> { };
diff --git a/tests/fixtures/wrapper/syntax_error.php b/tests/fixtures/wrapper/syntax_error.php
deleted file mode 100644
index f036819..0000000
--- a/tests/fixtures/wrapper/syntax_error.php
+++ /dev/null
@@ -1 +0,0 @@
-<?php { blah }
diff --git a/tests/fixtures/wrapper/type_alias.php b/tests/fixtures/wrapper/type_alias.php
deleted file mode 100644
index 5cc23b4..0000000
--- a/tests/fixtures/wrapper/type_alias.php
+++ /dev/null
@@ -1,17 +0,0 @@
-<?php namespace Yay\Fixtures\Wrapper;
-
-$(macro) {
-    type $(T_STRING as newtype) = $(T_STRING as basetype);
-} >> {
-    \\$(macro) {
-        \\$(either(instanceof, token(','), token('('), token(':')) as prec) $(newtype)
-    } >> {
-        \\$(prec) $(basetype)
-    }
-}
-
-type Path = string;
-
-function test_type_alias(Path $p) : Path {
-    return 'pass';
-}
diff --git a/tests/fixtures/wrapper/type_alias_absolute.php b/tests/fixtures/wrapper/type_alias_absolute.php
deleted file mode 100644
index cec2e63..0000000
--- a/tests/fixtures/wrapper/type_alias_absolute.php
+++ /dev/null
@@ -1,17 +0,0 @@
-<?php namespace Yay\Fixtures\Wrapper;
-
-$(macro) {
-    type $(T_STRING as newtype) = $(T_STRING as basetype);
-} >> {
-    \\$(macro) {
-        \\$(either(instanceof, token(','), token('('), token(':')) as prec) $(newtype)
-    } >> {
-        \\$(prec) $(basetype)
-    }
-}
-
-type Path = string;
-
-function test_type_alias_absolute(Path $p) : Path {
-    return 'pass';
-}
diff --git a/tests/phpt/errors/bad_dominant_macro_mark_end.phpt b/tests/phpt/errors/bad_dominant_macro_mark_end.phpt
index 3f38d85..e452a29 100644
--- a/tests/phpt/errors/bad_dominant_macro_mark_end.phpt
+++ b/tests/phpt/errors/bad_dominant_macro_mark_end.phpt
@@ -11,4 +11,4 @@ $(macro) {
 
 ?>
 --EXPECTF--
-Bad dominant macro marker '$!' offset 2 on line 4.
+Bad dominant macro marker '$!' offset 2, in %s.phpt on line 4.
diff --git a/tests/phpt/errors/bad_dominant_macro_mark_start.phpt b/tests/phpt/errors/bad_dominant_macro_mark_start.phpt
index 06ed2e5..97a929b 100644
--- a/tests/phpt/errors/bad_dominant_macro_mark_start.phpt
+++ b/tests/phpt/errors/bad_dominant_macro_mark_start.phpt
@@ -11,4 +11,4 @@ $(macro) {
 
 ?>
 --EXPECTF--
-Bad dominant macro marker '$!' offset 0 on line 4.
+Bad dominant macro marker '$!' offset 0, in %s.phpt on line 4.
diff --git a/tests/phpt/errors/bad_token_type.phpt b/tests/phpt/errors/bad_token_type.phpt
index 825ecb3..c12de3b 100644
--- a/tests/phpt/errors/bad_token_type.phpt
+++ b/tests/phpt/errors/bad_token_type.phpt
@@ -7,4 +7,4 @@ $(macro) { $(T_HAKUNAMATATA as foo) } >> { };
 
 ?>
 --EXPECTF--
-Undefined token type 'T_HAKUNAMATATA' on line 3.
+Undefined token type 'T_HAKUNAMATATA', in %s.phpt on line 3.
diff --git a/tests/phpt/errors/capture_redefinition.phpt b/tests/phpt/errors/capture_redefinition.phpt
index 86154ae..6e44930 100644
--- a/tests/phpt/errors/capture_redefinition.phpt
+++ b/tests/phpt/errors/capture_redefinition.phpt
@@ -11,4 +11,4 @@ $(macro) {
 
 ?>
 --EXPECTF--
-Redefinition of macro capture identifier 'foo' on line 4.
+Redefinition of macro capture identifier 'foo', in %s.phpt on line 4.
diff --git a/tests/phpt/errors/capture_without_type.phpt b/tests/phpt/errors/capture_without_type.phpt
index 3f6318d..9040d82 100644
--- a/tests/phpt/errors/capture_without_type.phpt
+++ b/tests/phpt/errors/capture_without_type.phpt
@@ -7,4 +7,4 @@ $(macro) { $(foo) } >> { $(foo) }
 
 ?>
 --EXPECTF--
-Bad macro capture identifier '$(foo)' on line 3.
+Bad macro capture identifier '$(foo)', in %s.phpt on line 3.
diff --git a/tests/phpt/errors/empty_expander_template.phpt b/tests/phpt/errors/empty_expander_template.phpt
deleted file mode 100644
index e1701fe..0000000
--- a/tests/phpt/errors/empty_expander_template.phpt
+++ /dev/null
@@ -1,16 +0,0 @@
---TEST--
-Empty expander template
---FILE--
-<?php
-
-$(macro) {
-    $(token(T_STRING) as foo)
-} >> {
-    $$(concat()) // forgot to pass $(foo)
-}
-
-SOME_T_STRING;
-
-?>
---EXPECTF--
-Empty expander slice on 'concat()' at line 6.
diff --git a/tests/phpt/errors/error_line_number.phpt b/tests/phpt/errors/error_line_number.phpt
index afa048e..833fded 100644
--- a/tests/phpt/errors/error_line_number.phpt
+++ b/tests/phpt/errors/error_line_number.phpt
@@ -29,4 +29,4 @@ foo; // L:25
 
 ?>
 --EXPECTF--
-Unexpected T_STRING(foo) on line 25, expected T_STRING(expected).
+Unexpected T_STRING(foo), in %s.phpt on line 25, expected T_STRING(expected).
diff --git a/tests/phpt/errors/expansion_undeclared.phpt b/tests/phpt/errors/expansion_undeclared.phpt
index 8ce2d23..002a097 100644
--- a/tests/phpt/errors/expansion_undeclared.phpt
+++ b/tests/phpt/errors/expansion_undeclared.phpt
@@ -16,7 +16,7 @@ $a >> $b;
 
 ?>
 --EXPECTF--
-Undefined macro expansion 'baz' on line 7 with context: [
+Undefined macro expansion 'baz', in %s.phpt on line 7 with context: [
     "foo",
     0,
     "bar"
diff --git a/tests/phpt/errors/macro_empty_pattern.phpt b/tests/phpt/errors/macro_empty_pattern.phpt
index ddfcff6..fbbab07 100644
--- a/tests/phpt/errors/macro_empty_pattern.phpt
+++ b/tests/phpt/errors/macro_empty_pattern.phpt
@@ -11,4 +11,4 @@ $(macro) {
 
 ?>
 --EXPECTF--
-Empty macro pattern on line 3.
+Empty macro pattern, in %s.phpt on line 3.
diff --git a/tests/phpt/errors/macro_without_expansion.phpt b/tests/phpt/errors/macro_without_expansion.phpt
index 3811b34..b50aed5 100644
--- a/tests/phpt/errors/macro_without_expansion.phpt
+++ b/tests/phpt/errors/macro_without_expansion.phpt
@@ -7,4 +7,4 @@ $(macro) { x } // bad macro, missing expansion section
 
 ?>
 --EXPECTF--
-Unexpected T_CLOSE_TAG(?>) on line 5, expected T_SR().
+Unexpected T_CLOSE_TAG(?>), in %s.phpt on line 5, expected T_SR().
diff --git a/tests/phpt/errors/missing_expander_argument.phpt b/tests/phpt/errors/missing_expander_argument.phpt
new file mode 100644
index 0000000..3f1615f
--- /dev/null
+++ b/tests/phpt/errors/missing_expander_argument.phpt
@@ -0,0 +1,17 @@
+--TEST--
+Test expander call with missing argument
+--FILE--
+<?php
+
+$(macro) {
+    match($(layer() as args))
+} >> {
+    $$(stringify(/* forgotten $(args) /o\ */))
+}
+
+match(foo);
+
+?>
+--EXPECTF--
+
+TokenStream expander call without tokens `$$(stringify())` as function Yay\DSL\Expanders\stringify(Yay\TokenStream $ts), in %s.phpt on line 6
diff --git a/tests/phpt/expanders/composition_tokenstream_expander.phpt b/tests/phpt/expanders/composition_tokenstream_expander.phpt
new file mode 100644
index 0000000..f338a70
--- /dev/null
+++ b/tests/phpt/expanders/composition_tokenstream_expander.phpt
@@ -0,0 +1,24 @@
+--TEST--
+Uses a custom fully qualified expansion function --pretty-print
+--FILE--
+<?php
+
+$(macro) {
+    hello($(token(T_STRING) as matched));
+} >> {
+    $$(\Yay\tests\fixtures\expanders\my_cheers_tokenstream_expander(
+    	$$(\Yay\tests\fixtures\expanders\my_hello_tokenstream_expander(
+    		$(matched)
+    	))
+    ));
+}
+
+hello(Chris);
+
+?>
+--EXPECTF--
+<?php
+
+'Hello, Chris. From TokenStream. Cheers!';
+
+?>
diff --git a/tests/phpt/expanders/error_when_undefined.phpt b/tests/phpt/expanders/error_when_undefined.phpt
index 8f5d350..684bab2 100644
--- a/tests/phpt/expanders/error_when_undefined.phpt
+++ b/tests/phpt/expanders/error_when_undefined.phpt
@@ -13,4 +13,4 @@ yay\undefined(...);
 
 ?>
 --EXPECTF--
-Bad macro expander 'undefined' on line 6.
+Bad macro expander 'undefined', in %s.phpt on line 6.
diff --git a/tests/phpt/expanders/fully_qualified_expander.phpt b/tests/phpt/expanders/fully_qualified_expander.phpt
index 2f666df..6536a4a 100644
--- a/tests/phpt/expanders/fully_qualified_expander.phpt
+++ b/tests/phpt/expanders/fully_qualified_expander.phpt
@@ -1,12 +1,12 @@
 --TEST--
-Uses a custom fully qualified expansion function
+Uses a custom fully qualified expansion function --pretty-print
 --FILE--
 <?php
 
 $(macro) {
-    hello($(token(T_STRING) as matched))
+    hello($(token(T_STRING) as matched));
 } >> {
-    $$(\Yay\tests\fixtures\expanders\my_hello_expander($(matched)))
+    $$(\Yay\tests\fixtures\expanders\my_hello_tokenstream_expander($(matched)));
 }
 
 hello(Chris);
@@ -15,6 +15,6 @@ hello(Chris);
 --EXPECTF--
 <?php
 
-'Hello, Chris';
+'Hello, Chris. From TokenStream.';
 
 ?>
diff --git a/tests/phpt/expanders/lazy_evaluation_of_expanders.phpt b/tests/phpt/expanders/lazy_evaluation_of_expanders.phpt
new file mode 100644
index 0000000..64bb20e
--- /dev/null
+++ b/tests/phpt/expanders/lazy_evaluation_of_expanders.phpt
@@ -0,0 +1,38 @@
+--TEST--
+Only evaluates custom expanders when required --pretty-print
+--FILE--
+<?php
+
+
+$(macro) {
+    $(
+        repeat(
+            either(
+                buffer("foo") as fooMatch,
+                buffer("bar") as barMatch
+            )
+        ) as matches
+    )
+} >> {
+    $(matches ... {
+        $(fooMatch ? {
+            $$(\Yay\tests\fixtures\expanders\my_foo_expander($(fooMatch)));
+        })
+
+        $(barMatch ? {
+            $$(\Yay\tests\fixtures\expanders\my_bar_expander($(barMatch)));
+        })
+    })
+}
+
+foo bar foo
+
+?>
+--EXPECTF--
+<?php
+
+'called Yay\\tests\\fixtures\\expanders\\my_foo_expander(foo)';
+'called Yay\\tests\\fixtures\\expanders\\my_bar_expander(bar)';
+'called Yay\\tests\\fixtures\\expanders\\my_foo_expander(foo)';
+
+?>
diff --git a/tests/phpt/issues/ircmaxell-php-compiler#29.phpt b/tests/phpt/issues/ircmaxell-php-compiler#29.phpt
new file mode 100644
index 0000000..549a7dd
--- /dev/null
+++ b/tests/phpt/issues/ircmaxell-php-compiler#29.phpt
@@ -0,0 +1,51 @@
+--TEST--
+Test for bug found at https://github.com/ircmaxell/php-compiler/pull/29 --pretty-print
+--FILE--
+<?php
+
+$(macro :unsafe :recursive) {
+    $(optional(buffer('unsigned')) as unsigned) compile {
+        $(
+            repeat(
+                either(
+                    chain(
+                        T_VARIABLE as result,
+                        token('='),
+                        either(
+                            chain(
+                                T_VARIABLE as binary_left,
+                                either(token('^') as binary_xor) as binary_op,
+                                either(T_VARIABLE as binary_variable, T_LNUMBER as binary_number) as binary_right
+                            ) as binary
+                        ),
+                        token(';')
+                    ) as assignop
+                )
+            ) as stmts
+        )
+    }
+} >> {
+    $(stmts ... {
+        $(assignop ? ... {
+            $(binary ? ... {
+                $(binary_op ... {
+                    $(binary_xor ? ... {
+                        $(result) = $this->context->builder->bitwiseXor($(binary_left), $__right);
+                    })
+                })
+            })
+        })
+    })
+}
+
+compile {
+    $result = $value ^ 1;
+}
+
+?>
+--EXPECTF--
+Error unpacking a non unpackable Ast node on `$(binary_xor?... {` at line 29 with context: [
+    "^"
+]
+
+Hint: use a non ellipsis expansion as in `$(binary_xor ? {`
diff --git a/tests/phpt/macro/dominant_macro.phpt b/tests/phpt/macro/dominant_macro.phpt
index 5aea4d0..790069b 100644
--- a/tests/phpt/macro/dominant_macro.phpt
+++ b/tests/phpt/macro/dominant_macro.phpt
@@ -14,4 +14,4 @@ entry_point_b { X => Y -> Z } // fails at "->"
 ?>
 --EXPECTF--
 
-Unexpected T_OBJECT_OPERATOR(->) on line 9, expected '}'.
+Unexpected T_OBJECT_OPERATOR(->), in %s.phpt on line 9, expected '}'.
diff --git a/tests/phpt/macro/layer_matcher_error_unbalanced.phpt b/tests/phpt/macro/layer_matcher_error_unbalanced.phpt
index 476829d..f989a5d 100644
--- a/tests/phpt/macro/layer_matcher_error_unbalanced.phpt
+++ b/tests/phpt/macro/layer_matcher_error_unbalanced.phpt
@@ -13,4 +13,4 @@ $(macro) {
 
 ?>
 --EXPECTF--
-Unexpected '}' on line 9, expected ']'.
+Unexpected '}', in %s.phpt on line 9, expected ']'.
diff --git a/tests/phpt/macro/layer_matcher_error_unbalanced_end.phpt b/tests/phpt/macro/layer_matcher_error_unbalanced_end.phpt
index 524e407..8ddbd73 100644
--- a/tests/phpt/macro/layer_matcher_error_unbalanced_end.phpt
+++ b/tests/phpt/macro/layer_matcher_error_unbalanced_end.phpt
@@ -13,4 +13,4 @@ $(macro) {
 
 ?>
 --EXPECTF--
-Unexpected end at T_CLOSE_TAG(?>) on line 11, expected ')'.
+Unexpected end at T_CLOSE_TAG(?>), in %s.phpt on line 11, expected ')'.
diff --git a/tests/phpt/macro/macro_deep_ast_access_error.phpt b/tests/phpt/macro/macro_deep_ast_access_error.phpt
index 7ed062c..5ab048b 100644
--- a/tests/phpt/macro/macro_deep_ast_access_error.phpt
+++ b/tests/phpt/macro/macro_deep_ast_access_error.phpt
@@ -38,6 +38,6 @@ match {
 
 ?>
 --EXPECTF--
-Undefined macro expansion 'level_a[level_b][level_c][leaf_level_x]' on line 27 with context: [
+Undefined macro expansion 'level_a[level_b][level_c][leaf_level_x]', in %s.phpt on line 27 with context: [
     "level_a"
 ]
diff --git a/tests/phpt/macro/operator_if_defined_then_expand_on_error_I.phpt b/tests/phpt/macro/operator_if_defined_then_expand_on_error_I.phpt
index 689fd03..9c95925 100644
--- a/tests/phpt/macro/operator_if_defined_then_expand_on_error_I.phpt
+++ b/tests/phpt/macro/operator_if_defined_then_expand_on_error_I.phpt
@@ -13,7 +13,7 @@ test;
 
 ?>
 --EXPECTF--
-Undefined macro expansion 'undefined' on line 6 with context: [
+Undefined macro expansion 'undefined', in %s.phpt on line 6 with context: [
     "foo",
     0
 ]
diff --git a/tests/phpt/macro/operator_if_not_defined_then_expand_on_error_I.phpt b/tests/phpt/macro/operator_if_not_defined_then_expand_on_error_I.phpt
index 2f89e20..1bd392d 100644
--- a/tests/phpt/macro/operator_if_not_defined_then_expand_on_error_I.phpt
+++ b/tests/phpt/macro/operator_if_not_defined_then_expand_on_error_I.phpt
@@ -13,7 +13,7 @@ test;
 
 ?>
 --EXPECTF--
-Undefined macro expansion 'bar' on line 6 with context: [
+Undefined macro expansion 'bar', in %s.phpt on line 6 with context: [
     "foo",
     0
 ]
diff --git a/tests/phpt/parsers/array_arg.phpt b/tests/phpt/parsers/array_arg.phpt
new file mode 100644
index 0000000..d9c6b81
--- /dev/null
+++ b/tests/phpt/parsers/array_arg.phpt
@@ -0,0 +1,135 @@
+--TEST--
+Test for constant array as parsec arguments
+--FILE--
+<?php
+
+$(macro) {
+
+    dummy
+
+    $(chain(
+        \Yay\tests\fixtures\parsers\var_dump_args_parser([]) as empty_array
+        ,
+        \Yay\tests\fixtures\parsers\var_dump_args_parser([1, '2', 'foo', 'bar', 5, []]) as non_assoc_array,
+        \Yay\tests\fixtures\parsers\var_dump_args_parser([
+            1, '2', 'foo', 'bar', 5, [1, '2', 'foo', 'bar', 5, []]
+        ]) as nested_non_assoc_array,
+        \Yay\tests\fixtures\parsers\var_dump_args_parser([
+            1 => 2, 3 => '4', '5' => 6, 'foo' => 'bar', 'baz' => [
+                1 => 2, 3 => '4', '5' => 6, 'foo' => 'bar', 'baz' => 7
+            ]
+        ]) as nested_assoc_array,
+        \Yay\tests\fixtures\parsers\var_dump_args_parser([[], ['foo' => []], 2 => ['bar' => [1, 2, 3]]]) as random_typing
+    ) as var_dump)
+
+    ;
+
+} >> {
+    $(var_dump)
+}
+
+dummy;
+
+?>
+--EXPECTF--
+<?php
+
+/*
+empty_array: array(0) {
+}
+*//*
+non_assoc_array: array(6) {
+  [0]=>
+  int(1)
+  [1]=>
+  string(1) "2"
+  [2]=>
+  string(3) "foo"
+  [3]=>
+  string(3) "bar"
+  [4]=>
+  int(5)
+  [5]=>
+  array(0) {
+  }
+}
+*//*
+nested_non_assoc_array: array(6) {
+  [0]=>
+  int(1)
+  [1]=>
+  string(1) "2"
+  [2]=>
+  string(3) "foo"
+  [3]=>
+  string(3) "bar"
+  [4]=>
+  int(5)
+  [5]=>
+  array(6) {
+    [0]=>
+    int(1)
+    [1]=>
+    string(1) "2"
+    [2]=>
+    string(3) "foo"
+    [3]=>
+    string(3) "bar"
+    [4]=>
+    int(5)
+    [5]=>
+    array(0) {
+    }
+  }
+}
+*//*
+nested_assoc_array: array(5) {
+  [1]=>
+  int(2)
+  [3]=>
+  string(1) "4"
+  [5]=>
+  int(6)
+  ["foo"]=>
+  string(3) "bar"
+  ["baz"]=>
+  array(5) {
+    [1]=>
+    int(2)
+    [3]=>
+    string(1) "4"
+    [5]=>
+    int(6)
+    ["foo"]=>
+    string(3) "bar"
+    ["baz"]=>
+    int(7)
+  }
+}
+*//*
+random_typing: array(3) {
+  [0]=>
+  array(0) {
+  }
+  [1]=>
+  array(1) {
+    ["foo"]=>
+    array(0) {
+    }
+  }
+  [2]=>
+  array(1) {
+    ["bar"]=>
+    array(3) {
+      [0]=>
+      int(1)
+      [1]=>
+      int(2)
+      [2]=>
+      int(3)
+    }
+  }
+}
+*/
+
+?>