diff --git a/src/collection.h b/src/collection.h
index b8e77b3..7817b36 100644
--- a/src/collection.h
+++ b/src/collection.h
@@ -147,7 +147,7 @@ class List : public TCollection, public Traits::Iterable, public Traits::Appenda
 public:
   using list_t = std::list<Value>;
   using utype_t = list_t;
-private:
+protected:
   list_t data;
   
 public:
@@ -196,6 +196,7 @@ class Stack : public List
   Stack() : List() { }
   Stack(const std::list<Value>& data) : List(data) { }
 
+  void put(Value value) override { data.push_front(value); }
 };
 
 class Queue : public List
@@ -203,6 +204,8 @@ class Queue : public List
 public:
   Queue() : List() { }
   Queue(const std::list<Value>& data) : List(data) { }
+
+  void put(Value value) override { data.push_back(value); }
 };
 
 #pragma mark Array
diff --git a/src/instruction.cpp b/src/instruction.cpp
index d92f33a..97841b5 100644
--- a/src/instruction.cpp
+++ b/src/instruction.cpp
@@ -157,41 +157,6 @@ void Instruction::execute(VM *vm) const
       }
       break;
     }
-   
-    case OP_QUESTION:
-    {
-      if (vm->popTwo(v1, v2))
-      {
-        {
-          switch (TYPES(v1.type, v2.type))
-          {
-            case TYPES(TYPE_BOOL,TYPE_LAMBDA):
-            {
-              if (v1.boolean())
-                vm->execute(v2.lambda()->code());
-              break;
-            }
-          }
-
-        }
-      }
-      break;
-    }
-    case OP_DQUESTION:
-    {
-      if (vm->popThree(v1, v2, v3))
-      {
-        if (v1.type == TYPE_BOOL && v2.type == TYPE_LAMBDA && v3.type == TYPE_LAMBDA)
-        {
-          if (v1.boolean())
-            vm->execute(v2.lambda()->code());
-          else
-            vm->execute(v3.lambda()->code());
-        }
-      }
-      break;
-    }
-      
 
     case OP_PEEK:
     {
@@ -381,54 +346,32 @@ void Instruction::execute(VM *vm) const
       
     case OP_HASH:
     {
-      if (vm->popTwo(v2, v3))
+      if (vm->popThree(v1, v2, v3))
       {
-        if (v2.type == TYPE_SET)
+        if (v1.type == TYPE_MAP)
         {
-          Set *set = v2.set();
-          set->put(v3);
-          vm->push(v2);
-        }
-        else if (v2.type == TYPE_STACK)
-        {
-          v2.stack()->raw().push_front(v3);
-          vm->push(v2);
-        }
-        else if (v2.type == TYPE_QUEUE)
-        {
-          v2.queue()->raw().push_back(v3);
-          vm->push(v2);
+          v1.map()->raw().emplace(std::make_pair(v2, v3));
+          vm->push(v1);
         }
         else
-        {
-          if (vm->popOne(v1))
+        {            
+          switch (TYPES(v1.type, v2.type))
           {
-            if (v1.type == TYPE_MAP)
+            case TYPES(TYPE_ARRAY, TYPE_INT):
             {
-              v1.map()->raw().emplace(std::make_pair(v2, v3));
-              vm->push(v1);
-            }
-            else
-            {            
-              switch (TYPES(v1.type, v2.type))
-              {
-                case TYPES(TYPE_ARRAY, TYPE_INT):
-                {
-                  auto& values = v1.array()->raw();
-                  integral_t i = v2.integral();
+              auto& values = v1.array()->raw();
+              integral_t i = v2.integral();
                   
-                  if (i >= values.size() && i >= values.capacity())
-                    values.resize(i+1, Value());
+              if (i >= values.size() && i >= values.capacity())
+                values.resize(i+1, Value());
                   
-                  values[v2.integral()] = v3;
+              values[v2.integral()] = v3;
                   
-                  vm->push(v1);
-                  break;
-                }
-              }
+              vm->push(v1);
+              break;
             }
           }
-        }      
+        }  
       }
       break;
     }
diff --git a/src/main.cpp b/src/main.cpp
index 04f5026..acee77a 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -38,7 +38,7 @@ int main (int argc, const char * argv[])
   string input;
   bool finished = false;
   
-  input = "(?0:[1]1:[1][1<>2<>+])2@";
+  /*input = "(?0:[1]1:[1][1<>2<>+])2@";
   compiler::Compiler compiler;
   Code*code = compiler.compile(input);
   if (code)
@@ -46,7 +46,7 @@ int main (int argc, const char * argv[])
     vm.execute(code);
     vm.printTopStack();
   }
-  return 0;
+  return 0;*/
 
   while (!finished)
   {
diff --git a/src/microcode.cpp b/src/microcode.cpp
index 3635c7f..b573377 100644
--- a/src/microcode.cpp
+++ b/src/microcode.cpp
@@ -9,6 +9,7 @@ using V = const Value&;
 void registerStackFunctions(MicroCode& mc);
 void registerNumericFunctions(MicroCode& mc);
 void registerStringFunctions(MicroCode& mc);
+void registerFlowFunctions(MicroCode& mc);
 
 SignatureArguments normalize(const SignatureArguments& args)
 {
@@ -324,6 +325,14 @@ void registerFunctions(MicroCode& mc)
                    
                    vm->push(true);
                  });
+
+  registerBinary(mc, Topic::COLLECTIONS, "append", "add an element to an appendable collection, following semantics of the collection", {}, 
+    { OP_HASH, TRAIT_ITERABLE, TRAIT_ANY_TYPE }, { TRAIT_ITERABLE },
+    [](VM* vm, V v1, V v2) {
+      Traits::Appendable* appendable = v1.appendable();
+      appendable->put(v2);
+      vm->pushCollection(v1);
+    });
   
   
   std::initializer_list<std::tuple<Opcode, Opcode, Opcode, std::string>> embedded_helpers = {
@@ -482,11 +491,10 @@ void registerFunctions(MicroCode& mc)
   registerUnary(mc, {OP_ANY, TYPE_TUPLE}, { TRAIT_ANY_TYPE }, [](VM* vm, V v1) { vm->push(v1.tuple()->at(0)); });
   registerUnary(mc, {OP_EVERY, TYPE_TUPLE}, { TRAIT_ANY_TYPE }, [](VM* vm, V v1) { vm->push(v1.tuple()->at(1)); });
 
-  
-
   registerStackFunctions(mc);
   registerNumericFunctions(mc);
   registerStringFunctions(mc);
+  registerFlowFunctions(mc);
 }
 
 namespace math
@@ -646,10 +654,11 @@ void registerFlowFunctions(MicroCode& mc)
                   Topic::LOGIC, "if-else", "executes first lambdfa if value on stack is true, second lambda otherwise",
                   {},
                   { OP_DQUESTION, TYPE_BOOL, TYPE_LAMBDA, TYPE_LAMBDA }, { },
+                  [] (VM* vm, V v1, V v2, V v3) {
                     if (v1.boolean())
-                    vm->execute(v2.lambda()->code());
+                      vm->execute(v2.lambda()->code());
                     else
-                    vm->execute(v3.lambda()->code());
+                      vm->execute(v3.lambda()->code());
                   });
 }
 
diff --git a/src/parser/impossible.l b/src/parser/impossible.l
index a6525fc..3e92737 100755
--- a/src/parser/impossible.l
+++ b/src/parser/impossible.l
@@ -33,6 +33,7 @@
 
 "(?" { return Parser::make_LARRAY_OPEN(loc); }
 "{>" { return Parser::make_STACK_OPEN(loc); }
+"{<" { return Parser::make_QUEUE_OPEN(loc); }
 
 "[[" { return Parser::make_TUPLE_OPEN(loc); }
 "]]" { return Parser::make_TUPLE_CLOSE(loc); }
diff --git a/src/parser/impossible.ypp b/src/parser/impossible.ypp
index 52231dd..3396e5e 100755
--- a/src/parser/impossible.ypp
+++ b/src/parser/impossible.ypp
@@ -3,7 +3,7 @@
 
 %defines
 %define api.namespace {compiler}
-%define parser_class_name {Parser}
+%define api.parser.class {Parser}
 
 %define api.token.constructor
 %define api.value.type variant
@@ -66,6 +66,7 @@
 
   LARRAY_OPEN "(?"
   STACK_OPEN "{>"
+  QUEUE_OPEN "{<"
 
   TUPLE_OPEN "[["
   TUPLE_CLOSE "]]"
@@ -243,8 +244,8 @@ value:
   | STACK_OPEN values RBRACE { $$ = new Stack($2); }
   | STACK_OPEN RBRACE { $$ = new Stack(); }
   
-  | LBRACE LESSER values RBRACE { $$ = new Queue($3); }
-  | LBRACE LESSER RBRACE { $$ = new Queue(); }
+  | QUEUE_OPEN values RBRACE { $$ = new Queue($2); }
+  | QUEUE_OPEN RBRACE { $$ = new Queue(); }
   
   | LBRACE PERIOD values RBRACE {
       $$ = new Set(Set::set_t($3.begin(), $3.end()));
diff --git a/src/value.cpp b/src/value.cpp
index d05493e..9e537d6 100644
--- a/src/value.cpp
+++ b/src/value.cpp
@@ -53,6 +53,7 @@ Error* Value::error() const { assert(type == TYPE_ERROR); return object<Error>()
 
 Traits::Indexable* Value::indexable() const { return object<Traits::Indexable>(); }
 Traits::Iterable* Value::iterable() const { return object<Traits::Iterable>(); }
+Traits::Appendable* Value::appendable() const { return object<Traits::Appendable>(); }
 
 
 Value Value::INVALID = Value(TYPE_INVALID);
diff --git a/src/value.h b/src/value.h
index 4f9312d..c2d397a 100644
--- a/src/value.h
+++ b/src/value.h
@@ -153,6 +153,7 @@ class Value final
   
   Traits::Indexable* indexable() const;
   Traits::Iterable* iterable() const;
+  Traits::Appendable* appendable() const;
 
   Lambda* lambda() const;
   
diff --git a/src/vm.h b/src/vm.h
index f3e720c..8b6f6a5 100644
--- a/src/vm.h
+++ b/src/vm.h
@@ -58,7 +58,7 @@ class VM
   const MicroCode& microcode;
   
 public:
-  VM(MicroCode& microcode) : valueStack(new stack_t()), exec(ActivationRecord()), running(false), stackPreserve(false), memory(),
+  VM(MicroCode& microcode) : valueStack(new stack_t()), exec(ActivationRecord()), running(false), stackPreserve(true), memory(),
   microcode(microcode)
   {
   }
@@ -68,11 +68,15 @@ class VM
     return exec.code;
   }
 
+  bool preserveCollectionOnStack() const { return stackPreserve; }
+
   void pushRecord(ActivationRecord&& record);
   void popRecord();
 
   const auto& record() const { return exec; }
   
+  void pushCollection(const Value& value) { if (preserveCollectionOnStack()) push(value); }
+
   void push(const Value& value)
   {
     valueStack->push_back(value);