wip: working on dynamic linking

- Feat: add example for wrapping dynamically linked library
- Feat: add new tokens (import, extern, type, handle, struct, ref, out)

.gdbinit

@@ -5,6 +5,7 @@ skip is
 skip -rfunction fzl_mk*
 skip -rfunction fzl_free*
 skip -rfunction fzl_symt*
+skip -rfunction fzl_linked*
 skip add_const
 skip push_op
 skip push_word

CMakeLists.txt

@@ -11,6 +11,13 @@ if (CMAKE_BUILD_TYPE STREQUAL "Debug")
 endif()
 
 include_directories(include)
+include(FetchContent)
+
+FetchContent_Declare(ffi
+	GIT_REPOSITORY "https://git.samsonium.dev/samsonium/libffi.git"
+	GIT_TAG "main"
+)
+FetchContent_MakeAvailable(ffi)
 
 # Compiler
 add_executable(fzc
@@ -56,6 +63,8 @@ add_executable(fz
 	src/vm/fzl_vm_debug.c
 	src/vm/main.c)
 
+target_link_libraries(fz PRIVATE ffi_static dl)
+
 #
 # ========== Tests ==========
 #

exl/linking.fzs

@@ -0,0 +1,38 @@
+extern "libglfw" {
+  type GLFWwindow  = handle;
+  type GLFWmonitor = handle;
+
+  struct GLFWvidmode {
+    int width;
+    int height;
+    int redBits;
+    int greenBits;
+    int blueBits;
+    int refreshRate;
+  }
+
+  /// GLFWvidmode*
+  type GLFWvidmodeRef = ref GLFWvidmode;
+
+  /// Create window with specified [width], [height] and [title]
+  fn glfw_mkWindow(
+    int width,
+    int height,
+    str title,
+    GLFWmonitor mon,
+    GLFWwindow shr
+  ) GLFWwindow = "glfwCreateWindow";
+
+  /// Get videomode from monitor [mon]
+  fn glfw_getVideoMode(
+    GLFWmonitor mon
+  ) GLFWvidmodeRef = "glfwGetVideoMode";
+
+  /// Get framebuffer [width] and [height]
+  fn glfw_getFrameBufferSize(
+    GLFWwindow win,
+    out int width,
+    out int height
+  ) = "glfwGetFramebufferSize";
+}
+

include/common/fzl_opcodes.h

@@ -35,6 +35,8 @@ typedef enum
   FZL_OPCODE_MOD = 0xA00006, // Get module of two numbers in dstack
   FZL_OPCODE_NEG = 0xA00007, // Negotiate number in dstack
 
+  FZL_OPCODE_BUILD_STR = 0xA10001, // Build a string from N values in dstack
+
   FZL_OPCODE_CMP_EQ   = 0xB00001, // Equal
   FZL_OPCODE_CMP_NEQ  = 0xB00002, // Not equal
   FZL_OPCODE_CMP_LT   = 0xB00003, // Less than

include/common/fzl_types.h

@@ -6,6 +6,8 @@ typedef enum
   FZL_TYPE_NULL,
   FZL_TYPE_OBJECT,
 
+  FZL_TYPE_EXTERN_FN,
+
   FZL_TYPE_STRING,
   FZL_TYPE_CHAR,
   FZL_TYPE_BOOL,

include/compiler/fzl_parser.h

@@ -11,6 +11,7 @@ typedef enum
   FZL_NODETYPE_BLOCK,
   FZL_NODETYPE_CALL,
   FZL_NODETYPE_LITERAL,
+  FZL_NODETYPE_FMT_STRING,
   FZL_NODETYPE_IDENTIFIER,
   FZL_NODETYPE_CONDITIONAL,
   FZL_NODETYPE_FUNCTION,

include/compiler/fzl_token.h

@@ -8,57 +8,68 @@
 // Token type
 typedef enum
 {
-  FZL_TOKTYPE_CLASS, // class
-  FZL_TOKTYPE_NEW,   // new
+  FZL_TOKTYPE_IMPORT,    // `import`
+  FZL_TOKTYPE_EXTERN,    // `extern`
+  FZL_TOKTYPE_TYPEDEF,   // `type`
+  FZL_TOKTYPE_HANDLE,    // `handle`
+  FZL_TOKTYPE_STRUCT,    // `struct`
+  FZL_TOKTYPE_REFERENCE, // `ref`
+  FZL_TOKTYPE_OUT,       // `out`
 
-  FZL_TOKTYPE_FUNCTION, // fn
-  FZL_TOKTYPE_RETURN,   // return
+  FZL_TOKTYPE_CLASS, // `class`
+  FZL_TOKTYPE_NEW,   // `new`
 
-  FZL_TOKTYPE_FOR,   // for
-  FZL_TOKTYPE_WHILE, // while
-  FZL_TOKTYPE_BREAK, // break
+  FZL_TOKTYPE_FUNCTION, // `fn`
+  FZL_TOKTYPE_RETURN,   // `return`
 
-  FZL_TOKTYPE_IF,   // if
-  FZL_TOKTYPE_ELSE, // else
+  FZL_TOKTYPE_FOR,   // `for`
+  FZL_TOKTYPE_WHILE, // `while`
+  FZL_TOKTYPE_BREAK, // `break`
+
+  FZL_TOKTYPE_IF,   // `if`
+  FZL_TOKTYPE_ELSE, // `else`
 
   FZL_TOKTYPE_NAME, // abc
   FZL_TOKTYPE_TYPE, // i16
 
-  FZL_TOKTYPE_DDASH, // // :D
+  FZL_TOKTYPE_DDASH, // `//` :D
 
-  FZL_TOKTYPE_LPAREN, // (
-  FZL_TOKTYPE_RPAREN, // )
-  FZL_TOKTYPE_LBRACE, // {
-  FZL_TOKTYPE_RBRACE, // }
+  FZL_TOKTYPE_LPAREN, // `(`
+  FZL_TOKTYPE_RPAREN, // `)`
+  FZL_TOKTYPE_LBRACE, // `{`
+  FZL_TOKTYPE_RBRACE, // `}`
 
-  FZL_TOKTYPE_COMMA,     // ,
-  FZL_TOKTYPE_DOT,       // .
-  FZL_TOKTYPE_SEMICOLON, // ;
+  FZL_TOKTYPE_COMMA,     // `,`
+  FZL_TOKTYPE_DOT,       // `.`
+  FZL_TOKTYPE_SEMICOLON, // `;`
 
   FZL_TOKTYPE_STR_LITERAL,  // ""
   FZL_TOKTYPE_NUM_LITERAL,  // 123
   FZL_TOKTYPE_BOOL_LITERAL, // true
   FZL_TOKTYPE_NULL_LITERAL, // null
 
-  FZL_TOKTYPE_DAMPERSAND, // &&
-  FZL_TOKTYPE_DVBAR,      // ||
+  FZL_TOKTYPE_STR_FORMAT_START, // `$` before `"`
+  FZL_TOKTYPE_STR_FORMAT_END,   // end of string formatting sequence
 
-  FZL_TOKTYPE_EQEQ,   // ==
-  FZL_TOKTYPE_REQ,    // >=
-  FZL_TOKTYPE_LEQ,    // <=
-  FZL_TOKTYPE_NEQ,    // !=
-  FZL_TOKTYPE_LANGLE, // <
-  FZL_TOKTYPE_RANGLE, // >
-  FZL_TOKTYPE_NOT,    // !
+  FZL_TOKTYPE_DAMPERSAND, // `&&`
+  FZL_TOKTYPE_DVBAR,      // `||`
 
-  FZL_TOKTYPE_STAR,    // *
-  FZL_TOKTYPE_SLASH,   // /
-  FZL_TOKTYPE_PLUS,    // +
-  FZL_TOKTYPE_MINUS,   // -
-  FZL_TOKTYPE_CARET,   // ^
-  FZL_TOKTYPE_PERCENT, // %
+  FZL_TOKTYPE_EQEQ,   // `==`
+  FZL_TOKTYPE_REQ,    // `>=`
+  FZL_TOKTYPE_LEQ,    // `<=`
+  FZL_TOKTYPE_NEQ,    // `!=`
+  FZL_TOKTYPE_LANGLE, // `<`
+  FZL_TOKTYPE_RANGLE, // `>`
+  FZL_TOKTYPE_NOT,    // `!`
 
-  FZL_TOKTYPE_EQ // =
+  FZL_TOKTYPE_STAR,    // `*`
+  FZL_TOKTYPE_SLASH,   // `/`
+  FZL_TOKTYPE_PLUS,    // `+`
+  FZL_TOKTYPE_MINUS,   // `-`
+  FZL_TOKTYPE_CARET,   // `^`
+  FZL_TOKTYPE_PERCENT, // `%`
+
+  FZL_TOKTYPE_EQ // `=`
 } fzl_toktype_t;
 
 // Token descriptor

include/vm/fzl_vm.h

@@ -6,6 +6,7 @@
 #include <stddef.h>
 #include <stdint.h>
 #include <vm/fzl_vm_env.h>
+#include <vm/fzl_vm_extern.h>
 #include <vm/fzl_vm_object.h>
 
 // VM descriptor
@@ -14,6 +15,9 @@ typedef struct
   fzl_const_t *consts;
   size_t consts_count;
 
+  fzl_vm_extern_t *externs;
+  size_t externs_count;
+
   uint64_t *ops;
   size_t ops_count;
 

include/vm/fzl_vm_extern.h

@@ -0,0 +1,14 @@
+#ifndef FZL_VM_EXTERN_H
+#define FZL_VM_EXTERN_H
+
+#include <ffi.h>
+
+// Loaded extern function definition
+typedef struct
+{
+  void *func_ptr;
+  ffi_cif cif;
+  ffi_type **arg_types;
+} fzl_vm_extern_t;
+
+#endif // FZL_VM_EXTERN_H

src/compiler/fzl_debug.c

@@ -31,6 +31,26 @@ void print_node(fzl_node_t *node, int level)
 
   switch (node->type)
   {
+    case FZL_NODETYPE_UNARY_MINUS:
+      printf("%s Unary '-':\n", levelbuf);
+      print_node(node->unary_op.operand, level + 1);
+      break;
+
+    case FZL_NODETYPE_UNARY_PLUS:
+      printf("%s Unary '+':\n", levelbuf);
+      print_node(node->unary_op.operand, level + 1);
+      break;
+
+    case FZL_NODETYPE_BREAK:
+      printf("%s Break\n", levelbuf);
+      break;
+
+    case FZL_NODETYPE_FMT_STRING:
+      printf("%s Format string:\n", levelbuf);
+      for (size_t i = 0; i < node->list.entry_count; i++)
+        print_node(node->list.entries[i], level + 1);
+      break;
+
     case FZL_NODETYPE_LOOP:
       printf("%s Loop:\n", levelbuf);
       printf("-%s Init:\n", levelbuf);
@@ -172,9 +192,6 @@ void print_node(fzl_node_t *node, int level)
     case FZL_NODETYPE_IDENTIFIER:
       printf("%s Identifier ('%s')\n", levelbuf, (char *)node->token->value);
       break;
-
-    default:
-      printf("%s Secure node\n", levelbuf);
   }
 }
 

src/compiler/fzl_parser.c

@@ -1,5 +1,5 @@
-#include "compiler/fzl_token.h"
 #include <compiler/fzl_parser.h>
+#include <compiler/fzl_token.h>
 #include <stdbool.h>
 #include <stddef.h>
 #include <stdio.h>
@@ -151,6 +151,99 @@ fzl_node_t *parse_primary(fzl_parser_t *parser)
     fzl_token_t *tok = consume(parser);
     return fzl_mknode(FZL_NODETYPE_LITERAL, tok);
   }
+  else if (is(parser, FZL_TOKTYPE_STR_FORMAT_START))
+  {
+    consume(parser);
+
+    size_t remainder     = 2;
+    size_t count         = 0;
+    fzl_node_t **entries = malloc(remainder * sizeof(fzl_node_t *));
+    if (!entries)
+    {
+      snprintf(plast_err, sizeof(plast_err), "out of memory");
+      return NULL;
+    }
+
+    while (peek(parser) && peek(parser)->type != FZL_TOKTYPE_STR_FORMAT_END)
+    {
+      if (is(parser, FZL_TOKTYPE_STR_FORMAT_END))
+        break;
+
+      if (remainder <= count)
+      {
+        remainder *= 2;
+        fzl_node_t **newentries =
+            realloc(entries, remainder * sizeof(fzl_node_t *));
+        if (!newentries)
+        {
+          snprintf(plast_err, sizeof(plast_err), "out of memory");
+          for (size_t i = 0; i < count; i++)
+            fzl_freeast(entries[i]);
+
+          free(entries);
+          return NULL;
+        }
+
+        entries = newentries;
+      }
+
+      fzl_node_t *expr = parse_expression(parser);
+      if (expr == NULL)
+      {
+        for (size_t i = 0; i < count; i++)
+          fzl_freeast(entries[i]);
+
+        free(entries);
+        return NULL;
+      }
+
+      entries[count++] = expr;
+    }
+
+    fzl_token_t *end = consume(parser);
+    if (end->type != FZL_TOKTYPE_STR_FORMAT_END)
+    {
+      snprintf(plast_err, sizeof(plast_err),
+               "'%s':%zu:%zu => unterminated format string",
+               last_known_tok->filename, last_known_tok->ln,
+               last_known_tok->cn);
+
+      for (size_t i = 0; i < count; i++)
+        fzl_freeast(entries[i]);
+
+      free(entries);
+    }
+
+    if (count < 1)
+    {
+      snprintf(plast_err, sizeof(plast_err),
+               "'%s':%zu:%zu => do you really need empty format string?",
+               last_known_tok->filename, last_known_tok->ln,
+               last_known_tok->cn);
+
+      for (size_t i = 0; i < count; i++)
+        fzl_freeast(entries[i]);
+
+      free(entries);
+      return NULL;
+    }
+
+    fzl_node_t *node = fzl_mknode(FZL_NODETYPE_FMT_STRING, entries[0]->token);
+    if (!node)
+    {
+      snprintf(plast_err, sizeof(plast_err), "out of memory");
+      for (size_t i = 0; i < count; i++)
+        fzl_freeast(entries[i]);
+
+      free(entries);
+      return NULL;
+    }
+
+    node->list.entries     = entries;
+    node->list.entry_count = count;
+
+    return node;
+  }
   else if (is(parser, FZL_TOKTYPE_LPAREN))
   {
     consume(parser);
@@ -559,8 +652,8 @@ fzl_node_t *parse_new(fzl_parser_t *parser)
 
   fzl_token_t *new    = consume(parser);
   fzl_node_t *objname = parse_or(parser);
-  if (objname->type != FZL_NODETYPE_IDENTIFIER &&
-      objname->type != FZL_NODETYPE_FIELD)
+  if (!objname || (objname->type != FZL_NODETYPE_IDENTIFIER &&
+                   objname->type != FZL_NODETYPE_FIELD))
   {
     fzl_freeast(objname);
     snprintf(plast_err, sizeof(plast_err),
@@ -1247,7 +1340,10 @@ fzl_node_t *parse_program(fzl_parser_t *parser)
   {
     node = parse_statement(parser);
     if (!node)
+    {
+      fzl_freeast(first);
       return NULL;
+    }
 
     if (!last)
     {
@@ -1308,11 +1404,11 @@ void fzl_freeast(fzl_node_t *root)
       case FZL_NODETYPE_LITERAL:
         break;
 
+      case FZL_NODETYPE_FMT_STRING:
       case FZL_NODETYPE_BLOCK:
         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);
@@ -1320,13 +1416,11 @@ void fzl_freeast(fzl_node_t *root)
         break;
 
       case FZL_NODETYPE_CALL:
-        if (root->call.callee)
         fzl_freeast(root->call.callee);
 
         if (root->call.args_count)
         {
           for (size_t i = 0; i < root->call.args_count; i++)
-            if (root->call.args[i])
             fzl_freeast(root->call.args[i]);
         }
         if (root->call.args)
@@ -1334,27 +1428,15 @@ void fzl_freeast(fzl_node_t *root)
         break;
 
       case FZL_NODETYPE_CONDITIONAL:
-        if (root->cond.condition)
         fzl_freeast(root->cond.condition);
-
-        if (root->cond.true_block)
         fzl_freeast(root->cond.true_block);
-
-        if (root->cond.else_block)
         fzl_freeast(root->cond.else_block);
         break;
 
       case FZL_NODETYPE_LOOP:
-        if (root->loop.init)
         fzl_freeast(root->loop.init);
-
-        if (root->loop.cond)
         fzl_freeast(root->loop.cond);
-
-        if (root->loop.step)
         fzl_freeast(root->loop.step);
-
-        if (root->loop.body)
         fzl_freeast(root->loop.body);
         break;
 
@@ -1373,16 +1455,13 @@ void fzl_freeast(fzl_node_t *root)
       case FZL_NODETYPE_GREATER:
       case FZL_NODETYPE_GREATER_EQUAL:
       case FZL_NODETYPE_ASSIGN:
-        if (root->binary_op.left)
         fzl_freeast(root->binary_op.left);
-        if (root->binary_op.right)
         fzl_freeast(root->binary_op.right);
         break;
 
       case FZL_NODETYPE_UNARY_PLUS:
       case FZL_NODETYPE_UNARY_MINUS:
       case FZL_NODETYPE_NOT:
-        if (root->unary_op.operand)
         fzl_freeast(root->unary_op.operand);
         break;
 
@@ -1395,7 +1474,6 @@ void fzl_freeast(fzl_node_t *root)
         break;
 
       case FZL_NODETYPE_RETURN:
-        if (root->ret.value)
         fzl_freeast(root->ret.value);
         break;
 
@@ -1421,7 +1499,6 @@ void fzl_freeast(fzl_node_t *root)
         break;
 
       case FZL_NODETYPE_DECLARATION:
-        if (root->var.identifier)
         fzl_freeast(root->var.identifier);
         break;
     }

src/compiler/fzl_reader.c

@@ -251,11 +251,83 @@ void skip_comment(fzl_reader_t *reader)
   }
 }
 
+// Parse string format
+fzl_token_t *parse_fmtstring_part(fzl_reader_t *reader)
+{
+  size_t p  = reader->position;
+  char *src = reader->source;
+
+  fzl_file_loc l;
+  bool ok = fzl_linked_getpos(reader->linked, reader->position, &l);
+  if (!ok)
+  {
+    snprintf(last_err, sizeof(last_err), "failed to locate line:col");
+    return NULL;
+  }
+
+  if (src[p] == '{')
+  {
+    move(reader, 1);
+    fzl_token_t *id = parse_name(reader);
+
+    if (id == NULL || src[reader->position] != '}')
+    {
+      snprintf(last_err, sizeof(last_err),
+               "'%s':%zu:%zu => failed to parse format string", l.filename,
+               l.line, l.col);
+      fzl_freetoken(id);
+      return NULL;
+    }
+
+    move(reader, 1);
+    return id;
+  }
+
+  if (src[p] == '"')
+  {
+    move(reader, 1);
+
+    return fzl_mktoken(FZL_TOKTYPE_STR_FORMAT_END, l.line, l.col, NULL, 0,
+                       l.filename);
+  }
+
+  size_t size = 0;
+  size_t lpos = p;
+
+  do
+  {
+    if (src[lpos + 1] == '"')
+      break;
+
+    size++;
+    lpos++;
+  } while (lpos < reader->size && reader->source[lpos] != '{' &&
+           reader->source[lpos] != '"');
+
+  ok = fzl_linked_getpos(reader->linked, reader->position, &l);
+  if (!ok)
+  {
+    snprintf(last_err, sizeof(last_err), "failed to locate line:col");
+    return NULL;
+  }
+
+  char *value = malloc(size);
+  memcpy(value, reader->source + reader->position, size);
+  fzl_token_t *tok = fzl_mktoken(FZL_TOKTYPE_STR_LITERAL, l.line, l.col, value,
+                                 size, l.filename);
+  free(value);
+  move(reader, size);
+
+  return tok;
+}
+
 int fzl_read(fzl_reader_t *reader)
 {
   if (reader->position >= reader->size)
     return 0;
 
+  bool is_format_str = false;
+
   do
   {
     size_t p = reader->position;
@@ -268,7 +340,13 @@ int fzl_read(fzl_reader_t *reader)
       continue;
     }
 
-    if (curr == '\'' || curr == '"')
+    if (is_format_str)
+    {
+      token = parse_fmtstring_part(reader);
+      if (token && token->type == FZL_TOKTYPE_STR_FORMAT_END)
+        is_format_str = false;
+    }
+    else if (curr == '\'' || curr == '"')
       token = parse_string_literal(reader);
     else if (curr == '/' && reader->source[p + 1] == '/')
     {
@@ -321,6 +399,12 @@ int fzl_read(fzl_reader_t *reader)
       token = add_single(reader, FZL_TOKTYPE_PERCENT);
     else if (curr == '=')
       token = add_single(reader, FZL_TOKTYPE_EQ);
+    else if (curr == '$' && reader->source[p + 1] == '"')
+    {
+      move(reader, 2);
+      is_format_str = true;
+      token = fzl_mktoken(FZL_TOKTYPE_STR_FORMAT_START, 0, 0, NULL, 0, "");
+    }
     else if ((curr >= 'A' && curr <= 'Z') || (curr >= 'a' && curr <= 'z') ||
              curr == '_')
       token = parse_name(reader);

src/compiler/fzl_token.c

@@ -30,7 +30,11 @@ fzl_token_t *fzl_mktoken(const fzl_toktype_t type, size_t line, size_t col,
 // Free allocated token
 void fzl_freetoken(fzl_token_t *tok)
 {
+  if (!tok)
+    return;
+
   if (tok->store_value)
     free(tok->value);
+
   free(tok);
 }

src/compiler/fzl_walker.c

@@ -203,6 +203,20 @@ fzl_walk_res_t walk(fzl_walker_t *walker, fzl_node_t *node)
   {
     switch (node->type)
     {
+      case FZL_NODETYPE_FMT_STRING:
+      {
+        for (size_t i = 0; i < node->list.entry_count; i++)
+        {
+          fzl_walk_res_t res = walk(walker, node->list.entries[i]);
+          if (res.error)
+            return res;
+        }
+
+        push_op(walker, FZL_OPCODE_BUILD_STR);
+        push_word(walker, node->list.entry_count);
+        break;
+      }
+
       case FZL_NODETYPE_BREAK:
       {
         fzl_walk_ctx_t *ctx = walker->ctx;

src/stdlib/bindings/conv.fzs

@@ -0,0 +1,6 @@
+/// Converts integer [value] to string
+extern fn itos(int value) str;
+
+/// Converts string [value] to integer
+extern fn stoi(str value) int;
+

src/stdlib/bindings/math.fzs

@@ -0,0 +1,6 @@
+/// Get the minimum of specified values
+extern fn min([]int ...values) int;
+
+/// Get the maximum of specified values
+extern fn max([]int ...values) int;
+

src/vm/fzl_vm.c

@@ -13,6 +13,7 @@
 #include <vm/fzl_vm_env.h>
 #include <vm/fzl_vm_object.h>
 
+char build_result[512];
 char last_err[256];
 size_t last_jmp_ip       = 0;
 size_t total_jmp_on_same = 0;
@@ -32,6 +33,8 @@ fzl_vm_t *fzl_mkvm(const char *filepath)
   vm->consts_count  = 0;
   vm->ops           = NULL;
   vm->ops_count     = 0;
+  vm->externs       = NULL;
+  vm->externs_count = 0;
   vm->ip            = 0;
   vm->dtop          = 0;
   vm->ctop          = 0;
@@ -63,6 +66,7 @@ fzl_vm_t *fzl_mkvm(const char *filepath)
   size_t consts_count, ops_count;
   fread(&consts_count, sizeof(size_t), 1, fd);
   fread(&ops_count, sizeof(size_t), 1, fd);
+  // TODO: read externs count
 
   if (ops_count < 1)
   {
@@ -116,6 +120,8 @@ fzl_vm_t *fzl_mkvm(const char *filepath)
     fread(&op, sizeof(uint64_t), 1, fd);
     vm->ops[i] = op;
   }
+
+  // TODO: read externs
   fclose(fd);
 
   return vm;
@@ -292,6 +298,139 @@ int fzl_vm_run(fzl_vm_t *vm, bool allow_infinite, uint64_t max_iter)
 
     switch (opcode)
     {
+      case FZL_OPCODE_BUILD_STR:
+      {
+        uint64_t n = vm->ops[++vm->ip];
+        if (vm->dtop < n)
+        {
+          snprintf(last_err, sizeof(last_err),
+                   "runtime error - expected %zu value(s) in dstack", n);
+          print_err_data(vm);
+          return -1;
+        }
+
+        char temp[64];
+        size_t gi = 0;
+        memset(build_result, 0, sizeof(build_result));
+        for (size_t i = 0; i < n; i++)
+        {
+          if (gi >= 512)
+          {
+            for (size_t i = 511; i > 508; i--)
+              build_result[i] = '.';
+            break;
+          }
+
+          memset(temp, 0, sizeof(temp));
+          fzl_value_t val = vm->dstack[i];
+
+          switch (val.type)
+          {
+            case FZL_TYPE_UINT:
+              snprintf(temp, sizeof(temp), "%zu", val.as.u);
+              strcpy(build_result + gi, temp);
+              gi += strlen(temp);
+              break;
+
+            case FZL_TYPE_UINT64:
+              snprintf(temp, sizeof(temp), "%lu", val.as.u64);
+              strcpy(build_result + gi, temp);
+              gi += strlen(temp);
+              break;
+
+            case FZL_TYPE_UINT32:
+              snprintf(temp, sizeof(temp), "%u", val.as.u32);
+              strcpy(build_result + gi, temp);
+              gi += strlen(temp);
+              break;
+
+            case FZL_TYPE_UINT16:
+              snprintf(temp, sizeof(temp), "%u", val.as.u16);
+              strcpy(build_result + gi, temp);
+              gi += strlen(temp);
+              break;
+
+            case FZL_TYPE_UINT8:
+              snprintf(temp, sizeof(temp), "%u", val.as.u8);
+              strcpy(build_result + gi, temp);
+              gi += strlen(temp);
+              break;
+
+            case FZL_TYPE_INT:
+              snprintf(temp, sizeof(temp), "%zd", val.as.i);
+              strcpy(build_result + gi, temp);
+              gi += strlen(temp);
+              break;
+
+            case FZL_TYPE_INT64:
+              snprintf(temp, sizeof(temp), "%ld", val.as.i64);
+              strcpy(build_result + gi, temp);
+              gi += strlen(temp);
+              break;
+
+            case FZL_TYPE_INT32:
+              snprintf(temp, sizeof(temp), "%d", val.as.i32);
+              strcpy(build_result + gi, temp);
+              gi += strlen(temp);
+              break;
+
+            case FZL_TYPE_INT16:
+              snprintf(temp, sizeof(temp), "%d", val.as.i16);
+              strcpy(build_result + gi, temp);
+              gi += strlen(temp);
+              break;
+
+            case FZL_TYPE_INT8:
+              snprintf(temp, sizeof(temp), "%d", val.as.i8);
+              strcpy(build_result + gi, temp);
+              gi += strlen(temp);
+              break;
+
+            case FZL_TYPE_BOOL:
+              snprintf(build_result + gi, sizeof(build_result) - gi, "%s",
+                       val.as.b ? "true" : "false");
+              gi += val.as.b ? 4 : 5;
+              break;
+
+            case FZL_TYPE_CHAR:
+              snprintf(build_result + gi, sizeof(build_result) - gi, "%d",
+                       val.as.c);
+              gi += 1;
+              break;
+
+            case FZL_TYPE_STRING:
+              snprintf(build_result + gi, sizeof(build_result) - gi, "%s",
+                       val.as.s.value);
+              gi += val.as.s.length;
+              break;
+
+            case FZL_TYPE_EXTERN_FN:
+              snprintf(temp, sizeof(temp), "<extern:%zu>", val.as.u);
+              strcpy(build_result + gi, temp);
+              gi += strlen(temp);
+              break;
+
+            case FZL_TYPE_OBJECT:
+              snprintf(temp, sizeof(temp), "<ref:%p>", val.as.obj);
+              strcpy(build_result + gi, temp);
+              gi += strlen(temp);
+              break;
+
+            case FZL_TYPE_NULL:
+              snprintf(build_result + gi, sizeof(build_result) - gi, "<null>");
+              gi += 6;
+              break;
+          }
+        }
+
+        vm->dtop -= n;
+        vm->dstack[vm->dtop++] =
+            (fzl_value_t){.type        = FZL_TYPE_STRING,
+                          .as.s.length = strlen(build_result),
+                          .as.s.value  = build_result};
+        break;
+      }
+
       case FZL_OPCODE_DEREFERENCE:
       {
         if (vm->dtop < 1)

src/vm/fzl_vm_debug.c

@@ -20,6 +20,10 @@ void fzl_vm_print_ops(fzl_vm_t *vm)
 
     switch (vm->ops[i])
     {
+      case FZL_OPCODE_BUILD_STR:
+        printf("BUILD_STR %zu\n", vm->ops[++i]);
+        break;
+
       case FZL_OPCODE_DEREFERENCE:
         printf("DEREFERENCE\n");
         break;
@@ -163,9 +167,6 @@ void fzl_vm_print_ops(fzl_vm_t *vm)
       case FZL_OPCODE_JMP:
         printf("JMP IP: %ld\n", vm->ops[++i]);
         break;
-
-      default:
-        printf("<UNKNOWN>\n");
     }
   }
 }

tests/programs/neg_fmtstr_with_unknown_inside.fzs

@@ -0,0 +1,2 @@
+printline($"Something's on the {way}")
+

tests/programs/neg_unterminatd_fmtstr.fzs

@@ -0,0 +1 @@
+$"jopa {abc}

tests/programs/pos_fmtstr.fzs

@@ -0,0 +1,6 @@
+int a1 = 2 * 2;
+printline($"First tests: build string and print. 2 * 2 = {a1}");
+
+str a2 = "Mike Tyson";
+printline($"Hello, {a2}");
+