diff --git a/CMakeLists.txt b/CMakeLists.txt
index 73f0dfd..4b60a09 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -12,6 +12,8 @@ add_executable(fzc
 	src/compiler/fzl_reader.c
 	src/compiler/fzl_parser.c
 	src/compiler/fzl_debug.c
+	src/compiler/fzl_walker.c
+	src/compiler/utils/fzl_const_pool.c
 	src/compiler/main.c)
 
 # VM
diff --git a/include/common/fzl_builtins.h b/include/common/fzl_builtins.h
new file mode 100644
index 0000000..678de31
--- /dev/null
+++ b/include/common/fzl_builtins.h
@@ -0,0 +1,9 @@
+#ifndef FZL_BUILTINS_H
+#define FZL_BUILTINS_H
+
+typedef enum
+{
+  FZL_BUILTIN_PRINTLINE // Print message in arg with newline at end
+} fzl_builtin_t;
+
+#endif // FZL_BUILTINS_H
diff --git a/include/common/fzl_opcodes.h b/include/common/fzl_opcodes.h
new file mode 100644
index 0000000..aab733f
--- /dev/null
+++ b/include/common/fzl_opcodes.h
@@ -0,0 +1,12 @@
+#ifndef FZL_OPCODES_H
+#define FZL_OPCODES_H
+
+// Available opcodes
+typedef enum
+{
+  FZL_OPCODE_LOADCONST,   // Load const into T (temp) reg
+  FZL_OPCODE_PUSHARG,     // Push argument from T into args stack
+  FZL_OPCODE_CALL_BUILTIN // Call builtin function
+} fzl_opcode_t;
+
+#endif // FZL_OPCODES_H
diff --git a/include/compiler/fzl_walker.h b/include/compiler/fzl_walker.h
new file mode 100644
index 0000000..0300873
--- /dev/null
+++ b/include/compiler/fzl_walker.h
@@ -0,0 +1,34 @@
+#ifndef FZL_WALKER_H
+#define FZL_WALKER_H
+
+#include <common/fzl_opcodes.h>
+#include <compiler/fzl_parser.h>
+#include <compiler/utils/fzl_const_pool.h>
+#include <stddef.h>
+
+// Walker descriptor
+typedef struct
+{
+  fzl_node_t *root;
+  fzl_const_hash_pool_t *consts;
+
+  uint64_t *ops;
+  size_t op_count;
+  size_t op_remainder;
+} fzl_walker_t;
+
+// Allocate new walker
+fzl_walker_t *fzl_mkwalker(fzl_node_t *root);
+
+// Walk throught the entire AST and build:
+// 1. Constants table
+// 2. Operations
+int fzl_walk(fzl_walker_t *walker);
+
+// Get last error message
+char *fzl_walker_geterror();
+
+// Free walker
+void fzl_freewalker(fzl_walker_t *walker);
+
+#endif // FZL_WALKER_H
diff --git a/include/compiler/utils/fzl_const_pool.h b/include/compiler/utils/fzl_const_pool.h
new file mode 100644
index 0000000..402a934
--- /dev/null
+++ b/include/compiler/utils/fzl_const_pool.h
@@ -0,0 +1,64 @@
+#ifndef FZL_CONST_SET_H
+#define FZL_CONST_SET_H
+
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdint.h>
+
+// Constant types
+typedef enum
+{
+  FZL_CONSTTYPE_STRING
+} fzl_consttype_t;
+
+// Constant descriptor
+typedef struct
+{
+  fzl_consttype_t type;
+
+  union
+  {
+    struct
+    {
+      const char *chars;
+      size_t length;
+    } string;
+  } as;
+} fzl_const_t;
+
+typedef struct
+{
+  size_t pool_index;
+} fzl_const_hash_slot_t;
+
+// Constant pool descriptor
+typedef struct
+{
+  fzl_const_t *array;
+  size_t size;
+  size_t capacity;
+
+  fzl_const_hash_slot_t *slots;
+  size_t slots_count;
+  size_t slots_capacity;
+} fzl_const_hash_pool_t;
+
+// Compare two constants for equality
+bool fzl_consts_equal(fzl_const_t a, fzl_const_t b);
+
+// Get hash of specified constant
+static uint32_t fzl_hash_const(fzl_const_t c);
+
+// Allocate constants hash pool
+fzl_const_hash_pool_t *fzl_mkconstpool();
+
+// Resize the hash table
+static void fzl_consts_pool_resize_hash(fzl_const_hash_pool_t *pool);
+
+// Push constant. Returns unique index
+size_t fzl_consts_pool_add(fzl_const_hash_pool_t *pool, fzl_const_t c);
+
+// Free constants hash pool
+void fzl_consts_pool_free(fzl_const_hash_pool_t *pool);
+
+#endif // FZL_CONST_SET_H
diff --git a/src/compiler/fzl_parser.c b/src/compiler/fzl_parser.c
index 0c1bbe6..b93ab88 100644
--- a/src/compiler/fzl_parser.c
+++ b/src/compiler/fzl_parser.c
@@ -2,13 +2,13 @@
 #include <stdio.h>
 #include <stdlib.h>
 
-char last_err[256];
+char plast_err[256];
 
 fzl_parser_t *fzl_mkparser(fzl_reader_ll_t *first)
 {
   if (!first)
   {
-    snprintf(last_err, sizeof(last_err), "token is null");
+    snprintf(plast_err, sizeof(plast_err), "token is null");
     return NULL;
   }
 
@@ -81,7 +81,7 @@ fzl_node_t *parse_primary(fzl_parser_t *parser)
     return fzl_mknode(FZL_NODETYPE_LITERAL, tok);
   }
 
-  snprintf(last_err, sizeof(last_err), "failed to parse primary at %d",
+  snprintf(plast_err, sizeof(plast_err), "failed to parse primary at %d",
            peek(parser)->i0);
   return NULL;
 }
@@ -126,7 +126,7 @@ fzl_node_t *parse_call(fzl_parser_t *parser)
       consume(parser);
     else if (peek(parser) && peek(parser)->type != FZL_TOKTYPE_RPAIR)
     {
-      snprintf(last_err, sizeof(last_err),
+      snprintf(plast_err, sizeof(plast_err),
                "expected ',' or ')' after arg list");
       return NULL;
     }
@@ -147,7 +147,7 @@ fzl_node_t *parse_expression(fzl_parser_t *parser, int precedence)
   else if (peek(parser) && peek(parser)->type == FZL_TOKTYPE_STR_LITERAL)
     return parse_primary(parser);
 
-  snprintf(last_err, sizeof(last_err), "failed to parse expression at %d",
+  snprintf(plast_err, sizeof(plast_err), "failed to parse expression at %d",
            peek(parser)->i0);
   return NULL;
 }
@@ -184,7 +184,7 @@ fzl_node_t *parse_program(fzl_parser_t *parser)
 
   if (!first)
   {
-    snprintf(last_err, sizeof(last_err), "empty ;(");
+    snprintf(plast_err, sizeof(plast_err), "empty ;(");
     return NULL;
   }
 
@@ -204,7 +204,7 @@ int fzl_parse(fzl_parser_t *parser)
 
 // --- Parse zone end ---
 
-char *fzl_parser_geterror() { return last_err; }
+char *fzl_parser_geterror() { return plast_err; }
 
 void fzl_freenode(fzl_node_t *node)
 {
@@ -220,17 +220,16 @@ void fzl_freeast(fzl_node_t *root)
 
   while (root)
   {
-    if (root->type == FZL_NODETYPE_BLOCK)
+    if (root->type == FZL_NODETYPE_BLOCK || root->type == FZL_NODETYPE_CALL)
     {
-      for (size_t i = 0; i < root->list.entry_count; i++)
-        if (root->list.entries[i])
-          fzl_freeast(root->list.entries[i]);
-    }
-    else if (root->type == FZL_NODETYPE_CALL)
-    {
-      for (size_t i = 0; i < root->list.entry_count; i++)
-        if (root->list.entries[i])
-          fzl_freeast(root->list.entries[i]);
+      if (root->list.entries)
+      {
+        for (size_t i = 0; i < root->list.entry_count; i++)
+          if (root->list.entries[i])
+            fzl_freeast(root->list.entries[i]);
+
+        free(root->list.entries);
+      }
     }
 
     fzl_freenode(root);
diff --git a/src/compiler/fzl_walker.c b/src/compiler/fzl_walker.c
new file mode 100644
index 0000000..46ad2cd
--- /dev/null
+++ b/src/compiler/fzl_walker.c
@@ -0,0 +1,168 @@
+#include <common/fzl_builtins.h>
+#include <common/fzl_opcodes.h>
+#include <compiler/fzl_parser.h>
+#include <compiler/fzl_walker.h>
+#include <compiler/utils/fzl_const_pool.h>
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+char wlast_err[256];
+
+fzl_walker_t *fzl_mkwalker(fzl_node_t *root)
+{
+  if (!root)
+  {
+    snprintf(wlast_err, sizeof(wlast_err), "root node is null");
+    return NULL;
+  }
+
+  fzl_walker_t *walker = malloc(sizeof(fzl_walker_t));
+  if (!walker)
+  {
+    snprintf(wlast_err, sizeof(wlast_err), "failed to allocated walker");
+    return NULL;
+  }
+
+  fzl_const_hash_pool_t *pool = fzl_mkconstpool();
+  if (!pool)
+  {
+    snprintf(wlast_err, sizeof(wlast_err), "failed to create constants pool");
+    return NULL;
+  }
+
+  walker->root = root;
+  walker->consts = pool;
+
+  walker->op_count = 0;
+  walker->op_remainder = 2;
+  walker->ops = malloc(walker->op_remainder * sizeof(uint64_t));
+
+  return walker;
+}
+
+// --- Walking zone ---
+
+// Add const to consts table
+size_t add_const(fzl_walker_t *walker, fzl_const_t c)
+{
+  if (!walker)
+    return false;
+  return fzl_consts_pool_add(walker->consts, c);
+}
+
+// Resize ops if size is equals to capacity
+void ops_resize_if_needed(fzl_walker_t *walker)
+{
+  if (!walker)
+    return;
+
+  if (walker->op_count >= walker->op_remainder)
+  {
+    walker->op_remainder *= 2;
+    walker->ops = realloc(walker->ops, walker->op_remainder * sizeof(uint64_t));
+  }
+}
+
+// Push opcode to operations array
+void push_op(fzl_walker_t *walker, fzl_opcode_t opcode)
+{
+  if (!walker)
+    return;
+
+  ops_resize_if_needed(walker);
+  walker->ops[walker->op_count++] = (uint64_t)opcode;
+}
+
+// Push 64-bit integer to operations array
+void push_word(fzl_walker_t *walker, uint64_t word)
+{
+  if (!walker)
+    return;
+
+  ops_resize_if_needed(walker);
+  walker->ops[walker->op_count++] = word;
+}
+
+bool walk(fzl_walker_t *walker, fzl_node_t *node)
+{
+  if (!walker || !node)
+    return false;
+
+  while (node != NULL)
+  {
+    switch (node->type)
+    {
+    case FZL_NODETYPE_BLOCK:
+      // NOTE: create block env here
+      if (node->list.entry_count > 0)
+        for (size_t i = 0; i < node->list.entry_count; i++)
+          walk(walker, node->list.entries[i]);
+      // NOTE: destroy block env here
+      break;
+
+    case FZL_NODETYPE_CALL:
+      if (node->list.entry_count > 0)
+      {
+        for (size_t i = 0; i < node->list.entry_count; i++)
+        {
+          walk(walker, node->list.entries[i]);
+          push_op(walker, FZL_OPCODE_PUSHARG);
+        }
+      }
+      // NOTE: you need to implement dynamic names call
+      push_op(walker, FZL_OPCODE_CALL_BUILTIN);
+
+      if (strcmp(node->token->value, "printline") == 0)
+        push_word(walker, FZL_BUILTIN_PRINTLINE);
+      else
+      {
+        snprintf(wlast_err, sizeof(wlast_err), "call to unknown function '%s'",
+                 (char *)node->token->value);
+        return false;
+      }
+      break;
+
+    case FZL_NODETYPE_LITERAL:
+      size_t n = add_const(
+          walker, (fzl_const_t){.type = FZL_CONSTTYPE_STRING,
+                                .as.string.chars = node->token->value,
+                                .as.string.length = node->token->value_sz});
+
+      push_op(walker, FZL_OPCODE_LOADCONST);
+      push_word(walker, n);
+      break;
+    }
+
+    node = node->next;
+  }
+
+  return true;
+}
+
+// Walk entire AST recursevily
+int fzl_walk(fzl_walker_t *walker)
+{
+  bool result = walk(walker, walker->root);
+  return !result && wlast_err[0] ? -1 : 0;
+}
+
+// --- Walking zone end ---
+
+char *fzl_walker_geterror() { return wlast_err; }
+
+void fzl_freewalker(fzl_walker_t *walker)
+{
+  if (!walker)
+    return;
+
+  fzl_consts_pool_free(walker->consts);
+
+  if (walker->ops)
+    free(walker->ops);
+
+  free(walker);
+}
diff --git a/src/compiler/main.c b/src/compiler/main.c
index c53ef42..3407ec0 100644
--- a/src/compiler/main.c
+++ b/src/compiler/main.c
@@ -1,6 +1,7 @@
 #include <compiler/fzl_debug.h>
 #include <compiler/fzl_parser.h>
 #include <compiler/fzl_reader.h>
+#include <compiler/fzl_walker.h>
 #include <stdbool.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -155,12 +156,35 @@ int main(int argc, char **argv)
   {
     printf("ok!\n");
     fzl_debug_print_ast(parser->root);
+    printf("-> walking AST...");
+  }
+
+  fzl_walker_t *walker = fzl_mkwalker(parser->root);
+  result = fzl_walk(walker);
+  if (result != 0)
+  {
+    printf("Error: %s\n", fzl_walker_geterror());
+    return -1;
+  }
+
+  if (args->verbose)
+  {
+    printf("ok!\n");
+
+    printf("--> Constants table:\n");
+    for (size_t i = 0; i < walker->consts->size; i++)
+      printf("---> %s\n", walker->consts->array[i].as.string.chars);
+
+    printf("--> Ops:\n");
+    for (size_t i = 0; i < walker->op_count; i++)
+      printf("---> %lu\n", walker->ops[i]);
   }
 
   free(args);
   fzl_freereader(rd);
   fzl_freeparser(parser);
   fzl_freeast(parser->root);
+  fzl_freewalker(walker);
 
   printf("done.\n");
   return 0;
diff --git a/src/compiler/utils/fzl_const_pool.c b/src/compiler/utils/fzl_const_pool.c
new file mode 100644
index 0000000..abb0d0b
--- /dev/null
+++ b/src/compiler/utils/fzl_const_pool.c
@@ -0,0 +1,140 @@
+#include <compiler/utils/fzl_const_pool.h>
+#include <stddef.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <string.h>
+
+bool fzl_consts_equal(fzl_const_t a, fzl_const_t b)
+{
+  if (a.type != b.type)
+    return false;
+
+  switch (a.type)
+  {
+  case FZL_CONSTTYPE_STRING:
+  {
+    if (a.as.string.length != b.as.string.length)
+      return false;
+
+    return memcmp(a.as.string.chars, b.as.string.chars, a.as.string.length) ==
+           0;
+  }
+  }
+
+  return false;
+}
+
+static uint32_t fzl_hash_const(fzl_const_t c)
+{
+  uint32_t hash = 2166136261u;
+  const uint8_t *data = NULL;
+  size_t size = 0;
+
+  switch (c.type)
+  {
+  case FZL_CONSTTYPE_STRING:
+    data = (const uint8_t *)&c.as.string.chars;
+    size = c.as.string.length;
+    break;
+  }
+
+  for (size_t i = 0; i < size; i++)
+  {
+    hash ^= data[i];
+    hash *= 16777619u;
+  }
+
+  return hash;
+}
+
+fzl_const_hash_pool_t *fzl_mkconstpool()
+{
+  fzl_const_hash_pool_t *pool = malloc(sizeof(fzl_const_hash_pool_t));
+
+  pool->size = 0;
+  pool->capacity = 8;
+  pool->array = malloc(pool->capacity * sizeof(fzl_const_t));
+
+  pool->slots_count = 0;
+  pool->slots_capacity = 16;
+  pool->slots = malloc(pool->slots_capacity * sizeof(fzl_const_hash_slot_t));
+  for (int i = 0; i < pool->slots_capacity; i++)
+    pool->slots[i].pool_index = -1;
+
+  return pool;
+}
+
+static void fzl_consts_pool_resize_hash(fzl_const_hash_pool_t *pool)
+{
+  int old_capacity = pool->slots_capacity;
+  fzl_const_hash_slot_t *old_slots = pool->slots;
+
+  pool->slots_capacity = old_capacity * 2;
+  pool->slots = malloc(pool->slots_capacity * sizeof(fzl_const_hash_slot_t));
+  for (int i = 0; i < pool->slots_capacity; i++)
+    pool->slots[i].pool_index = -1;
+  pool->slots_count = 0;
+
+  for (int i = 0; i < old_capacity; i++)
+  {
+    if (old_slots[i].pool_index == -1)
+      continue;
+
+    int index_in_pool = old_slots[i].pool_index;
+    fzl_const_t c = pool->array[index_in_pool];
+    uint32_t hash = fzl_hash_const(c);
+
+    uint32_t bucket = hash & (pool->slots_capacity - 1);
+    while (pool->slots[bucket].pool_index != -1)
+      bucket = (bucket + 1) & (pool->slots_capacity - 1);
+
+    pool->slots[bucket].pool_index = index_in_pool;
+    pool->slots_count++;
+  }
+
+  free(old_slots);
+}
+
+size_t fzl_consts_pool_add(fzl_const_hash_pool_t *pool, fzl_const_t c)
+{
+  if (pool->slots_count * 4 >= pool->slots_capacity * 3)
+    fzl_consts_pool_resize_hash(pool);
+
+  uint32_t hash = fzl_hash_const(c);
+  uint32_t bucket = hash & (pool->slots_capacity - 1);
+
+  while (pool->slots[bucket].pool_index != -1)
+  {
+    size_t existing_index = pool->slots[bucket].pool_index;
+    if (fzl_consts_equal(pool->array[existing_index], c))
+      return existing_index;
+
+    bucket = (bucket + 1) & (pool->slots_capacity - 1);
+  }
+
+  if (pool->size >= pool->capacity)
+  {
+    pool->capacity *= 2;
+    pool->array = (fzl_const_t *)realloc(pool->array,
+                                         pool->capacity * sizeof(fzl_const_t));
+  }
+
+  size_t new_index = pool->size;
+  pool->array[new_index] = c;
+  pool->size++;
+
+  pool->slots[bucket].pool_index = new_index;
+  pool->slots_count++;
+
+  return new_index;
+}
+
+void fzl_consts_pool_free(fzl_const_hash_pool_t *pool)
+{
+  if (!pool)
+    return;
+
+  free(pool->array);
+  free(pool->slots);
+  free(pool);
+}