diff --git a/07/examples/runtime1.c b/07/examples/runtime1.c
new file mode 100644
index 0000000..0157051
--- /dev/null
+++ b/07/examples/runtime1.c
@@ -0,0 +1,31 @@
+#include "../runtime.h"
+
+void f_add(struct stack* s) {
+    struct node_num* left = (struct node_num*) eval(stack_peek(s, 0));
+    struct node_num* right = (struct node_num*) eval(stack_peek(s, 1));
+    stack_push(s, (struct node_base*) alloc_num(left->value + right->value));
+}
+
+void f_main(struct stack* s) {
+    // PushInt 320
+    stack_push(s, (struct node_base*) alloc_num(320));
+
+    // PushInt 6
+    stack_push(s, (struct node_base*) alloc_num(6));
+
+    // PushGlobal f_add (the function for +)
+    stack_push(s, (struct node_base*) alloc_global(f_add, 2));
+
+    struct node_base* left;
+    struct node_base* right;
+    
+    // MkApp
+    left = stack_pop(s);
+    right = stack_pop(s);
+    stack_push(s, (struct node_base*) alloc_app(left, right));
+    
+    // MkApp
+    left = stack_pop(s);
+    right = stack_pop(s);
+    stack_push(s, (struct node_base*) alloc_app(left, right));
+}
diff --git a/07/runtime.c b/07/runtime.c
index 27f3848..6ee3cd6 100644
--- a/07/runtime.c
+++ b/07/runtime.c
@@ -1,48 +1,7 @@
 #include <stdint.h>
-#include <stdlib.h>
 #include <assert.h>
-
-struct stack;
-
-enum node_tag {
-    NODE_APP,
-    NODE_NUM,
-    NODE_GLOBAL,
-    NODE_IND,
-    NODE_PACK
-};
-
-struct node_base {
-    enum node_tag tag;
-};
-
-struct node_app {
-    struct node_base base;
-    struct node_base* left;
-    struct node_base* right;
-};
-
-struct node_num {
-    struct node_base base;
-    int32_t value;
-};
-
-struct node_global {
-    struct node_base base;
-    int32_t arity;
-    void (*function)(struct stack*);
-};
-
-struct node_ind {
-    struct node_base base;
-    struct node_base* next;
-};
-
-struct node_data {
-    struct node_base base;
-    int8_t tag;
-    struct node_base** array;
-};
+#include <memory.h>
+#include "runtime.h"
 
 struct node_base* alloc_node() {
     struct node_base* new_node = malloc(sizeof(struct node_app));
@@ -50,14 +9,38 @@ struct node_base* alloc_node() {
     return new_node;
 }
 
-struct stack {
-    size_t size;
-    size_t count;
-    struct node_base** data;
-};
+struct node_app* alloc_app(struct node_base* l, struct node_base* r) {
+    struct node_app* node = (struct node_app*) alloc_node();
+    node->base.tag = NODE_APP;
+    node->left = l;
+    node->right = r;
+    return node;
+}
+
+struct node_num* alloc_num(int32_t n) {
+    struct node_num* node = (struct node_num*) alloc_node();
+    node->base.tag = NODE_NUM;
+    node->value = n;
+    return node;
+}
+
+struct node_global* alloc_global(void (*f)(struct stack*), int32_t a) {
+    struct node_global* node = (struct node_global*) alloc_node();
+    node->base.tag = NODE_GLOBAL;
+    node->arity = a;
+    node->function = f;
+    return node;
+}
+
+struct node_ind* alloc_ind(struct node_base* n) {
+    struct node_ind* node = (struct node_ind*) alloc_node();
+    node->base.tag = NODE_IND;
+    node->next = n;
+    return node;
+}
 
 void stack_init(struct stack* s) {
-    s->size = 0;
+    s->size = 4;
     s->count = 0;
     s->data = malloc(sizeof(*s->data) * s->size);
     assert(s->data != NULL);
@@ -77,7 +60,7 @@ void stack_push(struct stack* s, struct node_base* n) {
 
 struct node_base* stack_pop(struct stack* s) {
     assert(s->count > 0);
-    s->count--;
+    return s->data[--s->count];
 }
 
 struct node_base* stack_peek(struct stack* s, size_t o) {
@@ -105,21 +88,73 @@ void stack_update(struct stack* s, size_t o) {
 
 void stack_alloc(struct stack* s, size_t o) {
     while(o--) {
-        struct node_ind* new_node = (struct node_ind*) alloc_node();
-        new_node->base.tag = NODE_IND;
-        new_node->next = NULL;
-        stack_push(s, (struct node_base*) new_node);
+        stack_push(s, (struct node_base*) alloc_ind(NULL));
     }
 }
 
-void eval(struct node_base* n);
+void stack_pack(struct stack* s, size_t n, int8_t t) {
+    assert(s->count >= n);
+
+    struct node_base** data = malloc(sizeof(*data) * n);
+    assert(data != NULL);
+    memcpy(data, &s->data[s->count - 1 - n], n * sizeof(*data));
+
+    struct node_data* new_node = (struct node_data*) alloc_node();
+    new_node->array = data;
+    new_node->base.tag = NODE_DATA;
+    new_node->tag = t;
+
+    stack_popn(s, n);
+    stack_push(s, (struct node_base*) new_node);
+}
+
+void stack_split(struct stack* s, size_t n) {
+    struct node_data* node = (struct node_data*) stack_pop(s);
+    for(size_t i = 0; i < n; i++) {
+        stack_push(s, node->array[i]);
+    }
+}
+
+void unwind(struct stack* s) {
+    while(1) {
+        struct node_base* peek = stack_peek(s, 0);
+        if(peek->tag == NODE_APP) {
+            struct node_app* n = (struct node_app*) peek;
+            stack_push(s, n->left);
+        } else if(peek->tag == NODE_GLOBAL) {
+            struct node_global* n = (struct node_global*) peek;
+            assert(s->count > n->arity);
+
+            for(size_t i = 1; i <= n->arity; i++) {
+                s->data[s->count - i]
+                    = ((struct node_app*) s->data[s->count - i - 1])->right;
+            }
+
+            n->function(s);
+        } else if(peek->tag == NODE_IND) {
+            struct node_ind* n = (struct node_ind*) peek;
+            stack_pop(s);
+            stack_push(s, n->next);
+        } else {
+            break;
+        }
+    }
+}
+
+struct node_base* eval(struct node_base* n) {
+    struct stack program_stack;
+    stack_init(&program_stack);
+    stack_push(&program_stack, n);
+    unwind(&program_stack);
+    struct node_base* result = stack_pop(&program_stack);
+    stack_free(&program_stack);
+    return result;
+}
 
 extern void f_main(struct stack* s);
 
 int main(int argc, char** argv) {
-    struct node_global* first_node = (struct node_global*) alloc_node();
-    first_node->base.tag = NODE_GLOBAL;
-    first_node->arity = 0;
-    first_node->function = f_main;
-    eval((struct node_base*) first_node);
+    struct node_global* first_node = alloc_global(f_main, 0);
+    struct node_base* result = eval((struct node_base*) first_node);
+    printf("%d\n", ((struct node_num*) result)->value);
 }
diff --git a/07/runtime.h b/07/runtime.h
new file mode 100644
index 0000000..2a585b1
--- /dev/null
+++ b/07/runtime.h
@@ -0,0 +1,69 @@
+#pragma once
+#include <stdlib.h>
+
+struct stack;
+
+enum node_tag {
+    NODE_APP,
+    NODE_NUM,
+    NODE_GLOBAL,
+    NODE_IND,
+    NODE_DATA
+};
+
+struct node_base {
+    enum node_tag tag;
+};
+
+struct node_app {
+    struct node_base base;
+    struct node_base* left;
+    struct node_base* right;
+};
+
+struct node_num {
+    struct node_base base;
+    int32_t value;
+};
+
+struct node_global {
+    struct node_base base;
+    int32_t arity;
+    void (*function)(struct stack*);
+};
+
+struct node_ind {
+    struct node_base base;
+    struct node_base* next;
+};
+
+struct node_data {
+    struct node_base base;
+    int8_t tag;
+    struct node_base** array;
+};
+
+struct node_base* alloc_node();
+struct node_app* alloc_app(struct node_base* l, struct node_base* r);
+struct node_num* alloc_num(int32_t n);
+struct node_global* alloc_global(void (*f)(struct stack*), int32_t a);
+struct node_ind* alloc_ind(struct node_base* n);
+
+struct stack {
+    size_t size;
+    size_t count;
+    struct node_base** data;
+};
+
+void stack_free(struct stack* s);
+void stack_push(struct stack* s, struct node_base* n);
+struct node_base* stack_pop(struct stack* s);
+struct node_base* stack_peek(struct stack* s, size_t o);
+void stack_popn(struct stack* s, size_t n);
+void stack_slide(struct stack* s, size_t n);
+void stack_update(struct stack* s, size_t o);
+void stack_alloc(struct stack* s, size_t o);
+void stack_pack(struct stack* s, size_t n, int8_t t);
+void stack_split(struct stack* s, size_t n);
+
+struct node_base* eval(struct node_base* n);