diff --git a/program.tf b/program.tf
index 5607a69..1026987 100644
--- a/program.tf
+++ b/program.tf
@@ -1 +1 @@
-5 10 20 + print
+5 10 + dup * print
diff --git a/toyforth.c b/toyforth.c
index 70801c9..0cd4230 100644
--- a/toyforth.c
+++ b/toyforth.c
@@ -2,6 +2,7 @@
 #include <stdlib.h>
 #include <string.h>
 #include <ctype.h>
+#include <assert.h>
 
 #define TFOBJ_TYPE_INT 0
 #define TFOBJ_TYPE_STR 1
@@ -10,6 +11,7 @@
 #define TFOBJ_TYPE_SYMBOL 4
 
 /* ############################# Data Structures ########################################## */
+
 typedef struct tfobj {
     int refcount;
     int type;  // TFOBJ_TYPE_*
@@ -18,6 +20,7 @@ typedef struct tfobj {
         struct {
             char *ptr;
             size_t len;
+            int quoted;
         } str;
         struct {
             struct tfobj **ele;
@@ -31,8 +34,24 @@ typedef struct tfparser {
     char *p;   // Next token to parse.
 } tfparser;
 
+/* Function table entry: each of this entry represents a symbol name
+ * associated with a function implementation.
+ */
+struct FunctionTableEntry {
+    tfobj *name;
+    void (*callback) (tfctx *ctx, tfobj *name);
+    tfobj *user_list;
+};
+
+struct FunctionTable {
+    struct FunctionTableEntry **func_table;
+    size_t func_count;
+};
+
+/* Our execution context. */
 typedef struct tfctx {
     tfobj *stack;
+    struct FunctionTable functable;
 } tfctx;
 
 /* ############################# Allocations wrappers ################################### */
@@ -47,6 +66,16 @@ void *xmalloc(size_t size)
     return ptr;
 }
 
+void *xrealloc(void *oldptr, size_t size)
+{
+    void *ptr = realloc(oldptr, size);
+    if (ptr == NULL) {
+        fprintf(stderr, "Out of memory allocating %zu bytes", size);
+        exit(1);
+    }
+    return ptr;
+}
+
 /* ######################### Object related functions ###################################
  * The following functions allocate Toy Forth objects of different types.
  */
@@ -91,6 +120,64 @@ tfobj *createSymbolObject(char *s, size_t len)
     return obj;
 }
 
+/* Free an object and all the other nested objects. */
+void freeObject(tfobj *obj) {
+    switch (obj->type) {
+    case TFOBJ_TYPE_LIST:
+        for (size_t j = 0; j < obj->list.len; j++) {
+            tfobj *ele = obj->list.ele[j];
+            release(ele);
+        }
+        break;
+    case TFOBJ_TYPE_SYMBOL:
+    case TFOBJ_TYPE_STR:
+        free(obj->str.ptr);
+        break;
+    }
+    free(obj);
+}
+
+void retain(tfobj *obj)
+{
+    obj->refcount++;
+}
+
+void release(tfobj *obj)
+{
+    assert(obj->refcount > 0);
+    obj->refcount--;
+    if (obj->refcount == 0)
+        freeObject(obj);
+}
+
+
+void printObject(tfobj *obj) {
+    switch (obj->type) {
+    case TFOBJ_TYPE_INT:
+        printf("%d", obj->i);
+        break;
+    case TFOBJ_TYPE_LIST:
+        printf("[");
+        for (size_t j = 0; j < obj->list.len; j++) {
+            tfobj *o = obj->list.ele[j];
+            printObject(o);
+            if (j != o->list.len-1)
+                printf(" ");
+        }
+        printf("]");
+        break;
+    case TFOBJ_TYPE_STR:
+        printf("\"%s\"", obj->str.ptr);
+        break;
+    case TFOBJ_TYPE_SYMBOL:
+        printf("%s", obj->str.ptr);
+        break;
+    default:
+        printf("?");
+        break;
+    }
+}
+
 /* ############################ List Object ############################################  */
 
 tfobj *createListObject(void)
@@ -106,7 +193,7 @@ tfobj *createListObject(void)
  * element added to the list, if needed. */
 void listPush(tfobj *l, tfobj *ele)
 {
-    l->list.ele = realloc(l->list.ele, sizeof(tfobj*) * (l->list.len+1));
+    l->list.ele = xrealloc(l->list.ele, sizeof(tfobj*) * (l->list.len+1));
     l->list.ele[l->list.len] = ele;
     l->list.len++;
 }
@@ -182,7 +269,7 @@ tfobj *compile(char *prg)
 
         // Check if the current token produced a parsing error.
         if (obj == NULL) {
-            // FIXME: release parsed here.
+            release(parsed);
             printf("Syntax error near: %32s ...\n", token_start);
             return NULL;
         } else {
@@ -193,28 +280,42 @@ tfobj *compile(char *prg)
     return parsed;
 }
 
-/* ############################ Execute the program ##################################### */
+/* ############################# Execution and context ################################## */
 
-void printObject(tfobj *obj) {
-    switch (obj->type) {
-    case TFOBJ_TYPE_INT:
-        printf("%d", obj->i);
-        break;
-    case TFOBJ_TYPE_LIST:
-        printf("[");
-        for (size_t j = 0; j < obj->list.len; j++) {
-            tfobj *o = obj->list.ele[j];
-            printObject(o);
-            printf(" ");
+tfctx *createContext(void)
+{
+    tfctx *ctx = xmalloc(sizeof(*ctx));
+    ctx->stack = createListObject();
+    ctx->functable.func_table = NULL;
+    ctx->functable.func_count = 0;
+    registerFunction(ctx, "+", basicMathFunctions);
+    return ctx;
+}
+
+/* Try to resolve and call the function associated with the symbol
+ * name 'word'. Return 0 if the symbol was actually bound to some
+ * function, return 1 otherwise.
+ */
+int callSymbol(tfctx *ctx, tfobj *word)
+{
+
+    return 0;
+}
+
+/* Execute the Toy Forth program stored into the list 'prg'. */
+void exec(tfctx *ctx, tfobj *prg) {
+    assert(prg->type == TFOBJ_TYPE_LIST);
+    for (size_t j = 0; j < prg->list.len; j++) {
+        tfobj *word = prg->list.ele[j];
+        switch (word->type) {
+        case TFOBJ_TYPE_SYMBOL:
+            callSymbol(ctx, word);
+            break;
+        default:
+            listPush(ctx->stack, word);
+            retain(word);
+            break;
         }
-        printf("]");
-        break;
-    case TFOBJ_TYPE_SYMBOL:
-        printf("'%s", obj->str.ptr);
-        break;
-    default:
-        printf("?");
-        break;
     }
 }
 
@@ -246,6 +347,14 @@ int main(int argc, char **argv)
 
     tfobj *prg = compile(prgtext);
     printObject(prg);
+    printf("\n");
+
+    tfctx *ctx = createContext();
+    exec(ctx, prg);
+
+    printf("Stack content at end: ");
+    printObject(ctx->stack);
+    printf("\n");
 
     return 0;
 }