feat: implement break

.gitignore

@@ -5,6 +5,7 @@
 !/exl
 !/include
 !/src
+!/tests
 
 # Files
 !/.clang-format

CMakeLists.txt

@@ -25,6 +25,7 @@ add_executable(fzc
 	src/compiler/utils/fzl_linked.c
 	src/compiler/utils/fzl_options.c
 	src/compiler/utils/fzl_ctable.c
+	src/compiler/checkers/fzl_loop_check.c
 	src/compiler/main.c)
 
 # Virtual machine
@@ -35,108 +36,31 @@ add_executable(fz
 	src/vm/main.c)
 
 #
-# ========== Compilation tests ==========
+# ========== Tests ==========
 #
 
 enable_testing()
 
-add_test(
+file(GLOB TEST_PROGS RELATIVE "${CMAKE_CURRENT_SOURCE_DIR}" "tests/programs/*.fzs")
-	NAME compile_hw
+foreach (TEST_FILE IN LISTS TEST_PROGS)
-	COMMAND fzc -o "${CMAKE_CURRENT_BINARY_DIR}/hw.fzb" "${CMAKE_CURRENT_SOURCE_DIR}/exl/hw.fzs"
+	get_filename_component(TEST_NAME "${TEST_FILE}" NAME_WE)
-)
-add_test(
-	NAME compile_print_empty
-	COMMAND fzc -o "${CMAKE_CURRENT_BINARY_DIR}/print_empty.fzb" "${CMAKE_CURRENT_SOURCE_DIR}/exl/print_empty.fzs"
-)
-add_test(
-	NAME compile_problematic_hw
-	COMMAND fzc -o "${CMAKE_CURRENT_BINARY_DIR}/problematic_hw.fzb" "${CMAKE_CURRENT_SOURCE_DIR}/exl/problematic_hw.fzs"
-)
-add_test(
-	NAME compile_base_math
-	COMMAND fzc -o "${CMAKE_CURRENT_BINARY_DIR}/base_math.fzb" "${CMAKE_CURRENT_SOURCE_DIR}/exl/base_math.fzs"
-)
-add_test(
-	NAME compile_variables
-	COMMAND fzc -o "${CMAKE_CURRENT_BINARY_DIR}/variables.fzb" "${CMAKE_CURRENT_SOURCE_DIR}/exl/variables.fzs"
-)
-add_test(
-	NAME compile_conditions
-	COMMAND fzc -o "${CMAKE_CURRENT_BINARY_DIR}/conditions.fzb" "${CMAKE_CURRENT_SOURCE_DIR}/exl/conditions.fzs"
-)
-add_test(
-	NAME compile_fn
-	COMMAND fzc -o "${CMAKE_CURRENT_BINARY_DIR}/fn.fzb" "${CMAKE_CURRENT_SOURCE_DIR}/exl/fn.fzs"
-)
-add_test(
-	NAME compile_comment
-	COMMAND fzc -o "${CMAKE_CURRENT_BINARY_DIR}/comment.fzb" "${CMAKE_CURRENT_SOURCE_DIR}/exl/comment.fzs"
-)
-add_test(
-	NAME compile_class
-	COMMAND fzc -o "${CMAKE_CURRENT_BINARY_DIR}/class.fzb" "${CMAKE_CURRENT_SOURCE_DIR}/exl/class.fzs"
-)
-add_test(
-	NAME compile_raii
-	COMMAND fzc -o "${CMAKE_CURRENT_BINARY_DIR}/raii.fzb" "${CMAKE_CURRENT_SOURCE_DIR}/exl/raii.fzs"
-)
-add_test(
-	NAME compile_borrow
-	COMMAND fzc -o "${CMAKE_CURRENT_BINARY_DIR}/borrow.fzb" "${CMAKE_CURRENT_SOURCE_DIR}/exl/borrow.fzs"
-)
-add_test(
-	NAME compile_hard_1
-	COMMAND fzc -o "${CMAKE_CURRENT_BINARY_DIR}/hard-1.fzb" "${CMAKE_CURRENT_SOURCE_DIR}/exl/hard-1.fzs"
-)
-
-set_tests_properties(compile_problematic_hw PROPERTIES WILL_FAIL TRUE)
-
-#
-# ========== Runtime tests ==========
-#
 	
 	add_test(
-	NAME runtime_hw
+		NAME "progs_compile_${TEST_NAME}"
-	COMMAND fz "${CMAKE_CURRENT_BINARY_DIR}/hw.fzb"
+		COMMAND fzc -o "${CMAKE_CURRENT_BINARY_DIR}/p_${TEST_NAME}.fzb" "${CMAKE_CURRENT_SOURCE_DIR}/${TEST_FILE}"
 	)
 	add_test(
-	NAME runtime_print_empty
+		NAME "progs_runtime_${TEST_NAME}"
-	COMMAND fz "${CMAKE_CURRENT_BINARY_DIR}/print_empty.fzb"
+		COMMAND fz "${CMAKE_CURRENT_BINARY_DIR}/p_${TEST_NAME}.fzb"
-)
-add_test(
-	NAME runtime_base_math
-	COMMAND fz "${CMAKE_CURRENT_BINARY_DIR}/base_math.fzb"
-)
-add_test(
-	NAME runtime_variables
-	COMMAND fz "${CMAKE_CURRENT_BINARY_DIR}/variables.fzb"
-)
-add_test(
-	NAME runtime_conditions
-	COMMAND fz "${CMAKE_CURRENT_BINARY_DIR}/conditions.fzb"
-)
-add_test(
-	NAME runtime_fn
-	COMMAND fz "${CMAKE_CURRENT_BINARY_DIR}/fn.fzb"
-)
-add_test(
-	NAME runtime_comment
-	COMMAND fz "${CMAKE_CURRENT_BINARY_DIR}/comment.fzb"
-)
-add_test(
-	NAME runtime_class
-	COMMAND fz "${CMAKE_CURRENT_BINARY_DIR}/class.fzb"
-)
-add_test(
-	NAME runtime_raii
-	COMMAND fz "${CMAKE_CURRENT_BINARY_DIR}/raii.fzb"
-)
-add_test(
-	NAME runtime_borrow
-	COMMAND fz "${CMAKE_CURRENT_BINARY_DIR}/borrow.fzb"
-)
-add_test(
-	NAME runtime_hard_1
-	COMMAND fz "${CMAKE_CURRENT_BINARY_DIR}/hard-1.fzb"
 	)
 
+	if (TEST_NAME MATCHES "neg_")
+		set_tests_properties("progs_compile_${TEST_NAME}" PROPERTIES WILL_FAIL TRUE)
+		set_tests_properties("progs_runtime_${TEST_NAME}" PROPERTIES WILL_FAIL TRUE)
+	endif()
+
+	if (TEST_NAME MATCHES "neg1_")
+		set_tests_properties("progs_runtime_${TEST_NAME}" PROPERTIES WILL_FAIL TRUE)
+	endif()
+endforeach()
+

Makefile

@@ -1,9 +1,11 @@
-.PHONY: configure build debug-c debug-vm test
+.PHONY: build debug-c debug-vm test
 
-configure:
+build:
 	cmake -S . -B build -DCMAKE_BUILD_TYPE=Debug
+	cmake --build build
 
-build: configure
+build-release:
+	cmake -S . -B build -DCMAKE_BUILD_TYPE=Release
 	cmake --build build
 
 debug-c: build

README.md

@@ -27,7 +27,7 @@ Working examples of code can be found in `exl/` directory.
 ## Building
 
 1. Clone the repository: `git clone https://git.samsonium.dev/samsonium/fz-lang.git`
-2. Build: `make build`
+2. Build: `make build-release`
 
 After this, a "build" directory will appear in the project root. It will contain two executable files:
 

README.ru.md

@@ -27,7 +27,7 @@
 ## Инструкции по сборке
 
 1. Склонировать проект: `git clone https://git.samsonium.dev/samsonium/fz-lang.git`
-2. Собрать проект: `make build`
+2. Собрать проект: `make build-release`
 
 После этого в корне появится директория **"build"**. В ней будут лежать два скомпилированных бинарных файла:
 

exl/00_variables.fzs

@@ -0,0 +1,32 @@
+// There are two ways to work with variables
+// 1. Declare variable:
+str someString = "world, hello!";
+
+// 2. Change variable value:
+someString = "hello, world!";
+
+// Variables helps you store values to use it later
+int a = 2;
+int b = a + a * a;
+int c = a * b;
+
+printline("Now we got 12:");
+printline(c);
+
+// Also, there is many different types to help your program
+//  work with many things:
+int signedInteger;
+uint unsignedInteger;
+str string;
+bool boolean;
+
+i8  integer1; // 8-byte int
+i16 integer2; // 16-byte int
+i32 integer3; // 32-byte int
+i64 integer4; // 64-byte int
+
+u8  integer5; // unsigned 8-byte integer
+u16 integer6; // unsigned 16-byte integer
+u32 integer7; // unsigned 32-byte integer
+u64 integer8; // unsigned 64-byte integer
+

exl/01_conditions.fzs

@@ -0,0 +1,30 @@
+// When you need to check some value
+//  a conditional statements might help you
+
+int valueToCheck = 2 + 2;
+if (valueToCheck == 4)
+{
+  printline("Yay! 2 + 2 = 4");
+}
+
+// Conditional statement uses condition in pairs
+//  after `if` keyword and executes command(s) after
+//  if condition turns out to be true
+
+// Otherwise, to execute block when condition turns
+//  out to be false, you can use `else` keyword:
+
+int age = 30;
+
+if (age <= 20)
+  printline("You're too young");
+else
+{
+  age = 20;
+  printline("You looks too young!");
+}
+
+// NOTE: If you need to execute only one statement
+//  inside `if` or `else` block, then the curly
+//  braces can be omitted.
+

exl/02_functions.fzs

@@ -0,0 +1,30 @@
+// If you have some code section which is
+//  duplicated in program several times
+//  then it means your program needs some
+//  functions!
+
+fn doSomeWork()
+{
+  printline("Some work");
+}
+
+// If the function makes some kind of
+//  calculations then you should specify
+//  the result type
+
+fn sum(int a, int b) int
+{
+  return a + b;
+}
+
+// The `return` keyword can be used to
+//  actually return the value from the
+//  function. Also, you can specify list
+//  of arguments that you will use inside
+//  the function
+
+int first = 5;
+int second = 6;
+int result = sum(first, second);
+printline(result);
+

include/compiler/fzl_parser.h

@@ -18,6 +18,8 @@ typedef enum
   FZL_NODETYPE_CLASS,
   FZL_NODETYPE_FIELD,
   FZL_NODETYPE_CONSTRUCT,
+  FZL_NODETYPE_LOOP,
+  FZL_NODETYPE_BREAK,
 
   FZL_NODETYPE_ADD,
   FZL_NODETYPE_SUB,
@@ -140,6 +142,16 @@ typedef struct fzl_node
     {
       struct fzl_node *name;
     } construct;
+
+    // Loop
+    struct
+    {
+      struct fzl_node *init;
+      struct fzl_node *cond;
+      struct fzl_node *step;
+
+      struct fzl_node *body;
+    } loop;
   };
 } fzl_node_t;
 

include/compiler/fzl_token.h

@@ -14,6 +14,10 @@ typedef enum
   FZL_TOKTYPE_FUNCTION, // fn
   FZL_TOKTYPE_RETURN,   // return
 
+  FZL_TOKTYPE_FOR,   // for
+  FZL_TOKTYPE_WHILE, // while
+  FZL_TOKTYPE_BREAK, // break
+
   FZL_TOKTYPE_IF,   // if
   FZL_TOKTYPE_ELSE, // else
 

include/compiler/fzl_walker.h

@@ -16,7 +16,8 @@ typedef enum
   FZL_WALK_CTX_TYPE_GLOBAL,
   FZL_WALK_CTX_TYPE_FN,
   FZL_WALK_CTX_TYPE_CLASS,
-  FZL_WALK_CTX_TYPE_ASSIGN
+  FZL_WALK_CTX_TYPE_ASSIGN,
+  FZL_WALK_CTX_TYPE_LOOP,
 } fzl_walk_ctx_type_t;
 
 // Internal walk function result
@@ -36,8 +37,23 @@ typedef struct fzl_walk_ctx
   fzl_walk_ctx_type_t type;
   struct fzl_walk_ctx *parent;
 
-  fzl_node_t *fn;
   size_t initial_env_lvl;
+  union
+  {
+    // function info
+    struct
+    {
+      fzl_node_t *fn;
+    };
+
+    // loops `break`s writeback addrs
+    struct
+    {
+      size_t *breaks;
+      size_t breaks_count;
+      size_t breaks_remainder;
+    };
+  };
 } fzl_walk_ctx_t;
 
 // Walker descriptor

src/compiler/checkers/fzl_loop_check.c

@@ -0,0 +1,227 @@
+#include <common/fzl_opcodes.h>
+#include <common/fzl_types.h>
+#include <compiler/fzl_parser.h>
+#include <compiler/fzl_walker.h>
+#include <compiler/utils/fzl_const_pool.h>
+#include <compiler/utils/fzl_symtable.h>
+#include <stdbool.h>
+#include <stdint.h>
+#include <string.h>
+
+ssize_t check_top;
+fzl_nodetype_t check_tree[256];
+
+void ghost_walk_changed(fzl_node_t *node, bool *changed, fzl_sym_t *sym)
+{
+  if (!node || !changed || *changed)
+    return;
+
+  check_tree[check_top++] = node->type;
+
+  switch (node->type)
+  {
+    case FZL_NODETYPE_BREAK:
+    case FZL_NODETYPE_DECLARATION:
+    case FZL_NODETYPE_CONSTRUCT:
+    case FZL_NODETYPE_CLASS:
+    case FZL_NODETYPE_FUNCTION:
+    case FZL_NODETYPE_LITERAL:
+      break;
+
+    case FZL_NODETYPE_UNARY_PLUS:
+    case FZL_NODETYPE_UNARY_MINUS:
+    case FZL_NODETYPE_NOT:
+      ghost_walk_changed(node->unary_op.operand, changed, sym);
+      break;
+
+    case FZL_NODETYPE_ADD:
+    case FZL_NODETYPE_SUB:
+    case FZL_NODETYPE_MUL:
+    case FZL_NODETYPE_DIV:
+    case FZL_NODETYPE_POW:
+    case FZL_NODETYPE_MOD:
+    case FZL_NODETYPE_OR:
+    case FZL_NODETYPE_AND:
+    case FZL_NODETYPE_EQUAL:
+    case FZL_NODETYPE_NEQUAL:
+    case FZL_NODETYPE_LESS:
+    case FZL_NODETYPE_LESS_EQUAL:
+    case FZL_NODETYPE_GREATER:
+    case FZL_NODETYPE_GREATER_EQUAL:
+    case FZL_NODETYPE_ASSIGN:
+      ghost_walk_changed(node->binary_op.left, changed, sym);
+      ghost_walk_changed(node->binary_op.right, changed, sym);
+      break;
+
+    case FZL_NODETYPE_FIELD:
+      ghost_walk_changed(node->memb.parent, changed, sym);
+      ghost_walk_changed(node->memb.field, changed, sym);
+      break;
+
+    case FZL_NODETYPE_RETURN:
+      ghost_walk_changed(node->ret.value, changed, sym);
+      break;
+
+    case FZL_NODETYPE_CONDITIONAL:
+      ghost_walk_changed(node->cond.condition, changed, sym);
+      ghost_walk_changed(node->cond.true_block, changed, sym);
+      ghost_walk_changed(node->cond.else_block, changed, sym);
+      break;
+
+    case FZL_NODETYPE_LOOP:
+      ghost_walk_changed(node->loop.cond, changed, sym);
+      ghost_walk_changed(node->loop.step, changed, sym);
+      ghost_walk_changed(node->loop.body, changed, sym);
+      break;
+
+    case FZL_NODETYPE_BLOCK:
+      for (size_t i = 0; i < node->list.entry_count; i++)
+        ghost_walk_changed(node->list.entries[i], changed, sym);
+      break;
+
+    case FZL_NODETYPE_CALL:
+      ghost_walk_changed(node->call.callee, changed, sym);
+      for (size_t i = 0; i < node->call.args_count; i++)
+        ghost_walk_changed(node->call.args[i], changed, sym);
+      break;
+
+    case FZL_NODETYPE_IDENTIFIER:
+      if (strcmp(node->token->value, sym->name) == 0)
+      {
+        *changed = true;
+      }
+
+      if (*changed)
+      {
+        *changed = false;
+        for (ssize_t i = check_top - 1; i >= 0; i--)
+        {
+          fzl_nodetype_t cur_t = check_tree[i];
+          if (cur_t == FZL_NODETYPE_ADD || cur_t == FZL_NODETYPE_SUB ||
+              cur_t == FZL_NODETYPE_MUL || cur_t == FZL_NODETYPE_DIV ||
+              cur_t == FZL_NODETYPE_POW || cur_t == FZL_NODETYPE_MOD ||
+              cur_t == FZL_NODETYPE_UNARY_MINUS)
+          {
+            *changed = true;
+            break;
+          }
+        }
+      }
+      break;
+  }
+
+  check_tree[--check_top] = 0;
+}
+
+// Whether value changed in loop body
+bool value_is_changed(fzl_node_t *node, fzl_sym_t *sym)
+{
+  if (!node || !sym)
+    return false;
+
+  bool changed = false;
+  check_top    = 0;
+  memset(check_tree, 0, sizeof(check_tree));
+  ghost_walk_changed(node, &changed, sym);
+
+  return changed;
+}
+
+// Try to find symbol in loop condition node
+bool retrieve_cond_sym(fzl_walker_t *walker, fzl_node_t *node, fzl_sym_t *sym)
+{
+  if (!walker || !node)
+    return false;
+
+  switch (node->type)
+  {
+    case FZL_NODETYPE_BREAK:
+    case FZL_NODETYPE_BLOCK:
+    case FZL_NODETYPE_CALL:
+    case FZL_NODETYPE_LITERAL:
+    case FZL_NODETYPE_CONDITIONAL:
+    case FZL_NODETYPE_FUNCTION:
+    case FZL_NODETYPE_RETURN:
+    case FZL_NODETYPE_CLASS:
+    case FZL_NODETYPE_FIELD:
+    case FZL_NODETYPE_CONSTRUCT:
+    case FZL_NODETYPE_LOOP:
+    case FZL_NODETYPE_ASSIGN:
+    case FZL_NODETYPE_DECLARATION:
+      return false;
+
+    case FZL_NODETYPE_UNARY_MINUS:
+    case FZL_NODETYPE_UNARY_PLUS:
+    case FZL_NODETYPE_NOT:
+      return retrieve_cond_sym(walker, node->unary_op.operand, sym);
+
+    case FZL_NODETYPE_ADD:
+    case FZL_NODETYPE_SUB:
+    case FZL_NODETYPE_MUL:
+    case FZL_NODETYPE_DIV:
+    case FZL_NODETYPE_POW:
+    case FZL_NODETYPE_MOD:
+    case FZL_NODETYPE_AND:
+    case FZL_NODETYPE_OR:
+    case FZL_NODETYPE_LESS:
+    case FZL_NODETYPE_LESS_EQUAL:
+    case FZL_NODETYPE_GREATER:
+    case FZL_NODETYPE_GREATER_EQUAL:
+    case FZL_NODETYPE_EQUAL:
+    case FZL_NODETYPE_NEQUAL:
+      if (retrieve_cond_sym(walker, node->binary_op.left, sym))
+        return true;
+      if (retrieve_cond_sym(walker, node->binary_op.right, sym))
+        return true;
+      return false;
+
+    case FZL_NODETYPE_IDENTIFIER:
+    {
+      bool exists;
+      for (ssize_t i = walker->sym_top - 1; i >= 0; i--)
+      {
+        if ((exists = fzl_symt_get(walker->syms[i], (char *)node->token->value,
+                                   sym)))
+          break;
+      }
+      return exists;
+    }
+  }
+
+  return false;
+}
+
+// Check for infinite loop
+bool is_infinite_loop(fzl_walker_t *walker, fzl_node_t *node, size_t start_ip,
+                      size_t end_ip)
+{
+  if (!walker)
+    return false;
+
+  end_ip = (end_ip >= walker->op_count) ? (walker->op_count - 1) : end_ip;
+
+  fzl_sym_t sym;
+  bool sym_exists = retrieve_cond_sym(walker, node->loop.cond, &sym);
+  if (sym_exists)
+  {
+    if (sym.type >= FZL_TYPE_INT8)
+    {
+      bool value_changed = value_is_changed(node, &sym);
+      if (value_changed)
+        return false;
+    }
+  }
+
+  // At least has jump outside
+  for (size_t i = start_ip; i <= end_ip; i++)
+  {
+    if (walker->ops[i] != FZL_OPCODE_JMP)
+      continue;
+
+    size_t jump_ip = walker->ops[++i];
+    if (jump_ip >= end_ip)
+      return false;
+  }
+
+  return true;
+}

src/compiler/fzl_debug.c

@@ -31,6 +31,22 @@ void print_node(fzl_node_t *node, int level)
 
   switch (node->type)
   {
+    case FZL_NODETYPE_LOOP:
+      printf("%s Loop:\n", levelbuf);
+      printf("-%s Init:\n", levelbuf);
+      if (node->loop.init)
+        print_node(node->loop.init, level + 2);
+      printf("-%s Condition:\n", levelbuf);
+      if (node->loop.cond)
+        print_node(node->loop.cond, level + 2);
+      printf("-%s Step:\n", levelbuf);
+      if (node->loop.step)
+        print_node(node->loop.step, level + 2);
+      printf("-%s Body:\n", levelbuf);
+      if (node->loop.body)
+        print_node(node->loop.body, level + 2);
+      break;
+
     case FZL_NODETYPE_CONSTRUCT:
       printf("%s Construct class '%s':\n", levelbuf,
              (char *)node->construct.name->token->value);
@@ -169,7 +185,7 @@ void fzl_debug_print_ast(fzl_node_t *root)
   fzl_node_t *curr = root;
   while (curr != NULL)
   {
-    print_node(curr, 2);
+    print_node(curr, 3);
     curr = curr->next;
   }
 

src/compiler/fzl_parser.c

@@ -30,10 +30,7 @@ fzl_token_t this_tok = {.type        = FZL_TOKTYPE_NAME,
 fzl_parser_t *fzl_mkparser(fzl_reader_ll_t *first)
 {
   if (!first)
-  {
-    snprintf(plast_err, sizeof(plast_err), "token is null");
     return NULL;
-  }
 
   fzl_parser_t *parser = malloc(sizeof(fzl_parser_t));
   if (!parser)
@@ -162,6 +159,7 @@ fzl_node_t *parse_primary(fzl_parser_t *parser)
     {
       snprintf(plast_err, sizeof(plast_err), "'%s': expected ')' at %ld:%ld",
                peek(parser)->filename, peek(parser)->ln, peek(parser)->cn);
+      fzl_freeast(node);
       return NULL;
     }
     consume(parser);
@@ -259,6 +257,7 @@ fzl_node_t *parse_postfix(fzl_parser_t *parser)
         if (!rparen || rparen->type != FZL_TOKTYPE_RPAREN)
         {
           free(args);
+          fzl_freeast(left);
           snprintf(plast_err, sizeof(plast_err),
                    "'%s': expected ')' after argument list at %ld:%ld",
                    peek(parser)->filename, peek(parser)->ln, peek(parser)->cn);
@@ -276,6 +275,7 @@ fzl_node_t *parse_postfix(fzl_parser_t *parser)
       {
         if (!is(parser, FZL_TOKTYPE_NAME))
         {
+          fzl_freeast(left);
           snprintf(plast_err, sizeof(plast_err),
                    "'%s': expected name after '.' at %ld:%ld",
                    last_known_tok->filename, last_known_tok->ln,
@@ -342,6 +342,7 @@ fzl_node_t *parse_power(fzl_parser_t *parser)
     right = parse_unary(parser);
     if (!right)
     {
+      fzl_freeast(left);
       if (!plast_err[0])
         snprintf(plast_err, sizeof(plast_err),
                  "'%s': failed to parse right side of power at %ld:%ld",
@@ -385,6 +386,7 @@ fzl_node_t *parse_factor(fzl_parser_t *parser)
     right = parse_factor(parser);
     if (!right)
     {
+      fzl_freeast(left);
       if (!plast_err[0])
         snprintf(plast_err, sizeof(plast_err),
                  "'%s': unfinished factor (mul/div) expression at %ld:%ld",
@@ -426,6 +428,7 @@ fzl_node_t *parse_term(fzl_parser_t *parser)
     right = parse_factor(parser);
     if (!right)
     {
+      fzl_freeast(left);
       if (!plast_err[0])
         snprintf(plast_err, sizeof(plast_err),
                  "'%s': unfinished term (add/sub) expression at %ld:%ld",
@@ -462,6 +465,7 @@ fzl_node_t *parse_cond(fzl_parser_t *parser)
     right           = parse_term(parser);
     if (!right)
     {
+      fzl_freeast(left);
       if (!plast_err[0])
         snprintf(plast_err, sizeof(plast_err),
                  "'%s': unfinished expression at %ld:%ld", op->filename, op->ln,
@@ -520,6 +524,7 @@ fzl_node_t *parse_and(fzl_parser_t *parser)
     right            = parse_cond(parser);
     if (!right)
     {
+      fzl_freeast(left);
       if (!plast_err[0])
         snprintf(plast_err, sizeof(plast_err),
                  "'%s': unfinished expression at %ld:%ld", or->filename, or->ln,
@@ -554,6 +559,7 @@ fzl_node_t *parse_or(fzl_parser_t *parser)
     right            = parse_and(parser);
     if (!right)
     {
+      fzl_freeast(left);
       if (!plast_err[0])
         snprintf(plast_err, sizeof(plast_err),
                  "'%s': unfinished expression at %ld:%ld", or->filename, or->ln,
@@ -581,6 +587,7 @@ fzl_node_t *parse_new(fzl_parser_t *parser)
   if (objname->type != FZL_NODETYPE_IDENTIFIER &&
       objname->type != FZL_NODETYPE_FIELD)
   {
+    fzl_freeast(objname);
     snprintf(plast_err, sizeof(plast_err),
              "'%s': expect class name after 'new' keyword at %ld:%ld",
              last_known_tok->filename, last_known_tok->ln, last_known_tok->cn);
@@ -607,6 +614,7 @@ fzl_node_t *parse_assignment(fzl_parser_t *parser)
         left->type != FZL_NODETYPE_DECLARATION &&
         left->type != FZL_NODETYPE_FIELD)
     {
+      fzl_freeast(left);
       snprintf(plast_err, sizeof(plast_err),
                "'%s': cannot assign to '%s' at %ld:%ld", left->token->filename,
                (char *)left->token->value, asn->ln, asn->cn);
@@ -615,7 +623,10 @@ fzl_node_t *parse_assignment(fzl_parser_t *parser)
 
     fzl_node_t *right = parse_assignment(parser);
     if (!right)
+    {
+      fzl_freeast(left);
       return NULL;
+    }
 
     fzl_node_t *node      = fzl_mknode(FZL_NODETYPE_ASSIGN, asn);
     node->binary_op.left  = left;
@@ -695,6 +706,7 @@ fzl_node_t *parse_class(fzl_parser_t *parser)
         fields = realloc(fields, fremainder * sizeof(fzl_node_t *));
         if (!fields)
         {
+          fzl_freeast(node);
           snprintf(plast_err, sizeof(plast_err),
                    "failed to resize fields array");
           free(methods);
@@ -712,6 +724,7 @@ fzl_node_t *parse_class(fzl_parser_t *parser)
         methods = realloc(methods, mremainder * sizeof(fzl_node_t *));
         if (!methods)
         {
+          fzl_freeast(node);
           snprintf(plast_err, sizeof(plast_err),
                    "failed to resize methods array");
           free(fields);
@@ -726,6 +739,7 @@ fzl_node_t *parse_class(fzl_parser_t *parser)
         snprintf(plast_err, sizeof(plast_err),
                  "failed to reallocate method args list");
         free(fields);
+        fzl_freeast(node);
         return NULL;
       }
 
@@ -744,6 +758,7 @@ fzl_node_t *parse_class(fzl_parser_t *parser)
     }
     else
     {
+      fzl_freeast(node);
       snprintf(plast_err, sizeof(plast_err),
                "'%s': unknown type of class member at %ld:%ld",
                node->token->filename, node->token->ln, node->token->cn);
@@ -830,6 +845,7 @@ fzl_node_t *parse_function(fzl_parser_t *parser)
   fzl_token_t *rpar = consume(parser);
   if (!rpar || rpar->type != FZL_TOKTYPE_RPAREN)
   {
+    free(args);
     snprintf(plast_err, sizeof(plast_err),
              "'%s': expected ')' after argument list at %ld:%ld",
              last_known_tok->filename, last_known_tok->ln, last_known_tok->cn);
@@ -845,6 +861,7 @@ fzl_node_t *parse_function(fzl_parser_t *parser)
 
   if (!is(parser, FZL_TOKTYPE_LBRACE))
   {
+    free(args);
     snprintf(plast_err, sizeof(plast_err),
              "'%s': expected '{' after function declaration at %ld:%ld",
              last_known_tok->filename, last_known_tok->ln, last_known_tok->cn);
@@ -853,7 +870,10 @@ fzl_node_t *parse_function(fzl_parser_t *parser)
 
   fzl_node_t *body = parse_statement(parser);
   if (!body)
+  {
+    free(args);
     return NULL;
+  }
 
   fzl_node_t *node    = fzl_mknode(FZL_NODETYPE_FUNCTION, name);
   node->fn.args       = args;
@@ -878,7 +898,10 @@ fzl_node_t *parse_return(fzl_parser_t *parser)
   {
     fzl_node_t *retval = parse_expression(parser);
     if (!retval)
+    {
+      fzl_freeast(node);
       return NULL;
+    }
 
     node->ret.value = retval;
   }
@@ -908,6 +931,7 @@ fzl_node_t *parse_if(fzl_parser_t *parser)
   fzl_token_t *rparen = consume(parser);
   if (rparen->type != FZL_TOKTYPE_RPAREN)
   {
+    fzl_freeast(condition);
     snprintf(plast_err, sizeof(plast_err),
              "'%s': expected ')' after condition at %ld:%ld", rparen->filename,
              rparen->ln, rparen->cn);
@@ -917,15 +941,22 @@ fzl_node_t *parse_if(fzl_parser_t *parser)
   fzl_node_t *else_block = NULL;
   fzl_node_t *true_block = parse_statement(parser);
   if (!true_block)
+  {
+    fzl_freeast(condition);
     return NULL;
+  }
 
   if (is(parser, FZL_TOKTYPE_ELSE))
   {
     consume(parser); // else
     else_block = parse_statement(parser);
     if (!else_block)
+    {
+      fzl_freeast(condition);
+      fzl_freeast(true_block);
       return NULL;
     }
+  }
 
   fzl_node_t *stmt_node      = fzl_mknode(FZL_NODETYPE_CONDITIONAL, if_tok);
   stmt_node->cond.condition  = condition;
@@ -951,7 +982,10 @@ fzl_node_t *parse_block(fzl_parser_t *parser)
   {
     fzl_node_t *node = parse_statement(parser);
     if (!node)
+    {
+      free(stmts);
       return NULL;
+    }
 
     if (remainder <= count)
     {
@@ -962,8 +996,12 @@ fzl_node_t *parse_block(fzl_parser_t *parser)
     stmts[count++] = node;
   }
   fzl_token_t *rbrace = consume(parser);
-  if (rbrace && rbrace->type != FZL_TOKTYPE_RBRACE)
+  if (!rbrace || rbrace->type != FZL_TOKTYPE_RBRACE)
   {
+    for (size_t i = 0; i < count; i++)
+      fzl_freeast(stmts[i]);
+    free(stmts);
+
     snprintf(plast_err, sizeof(plast_err),
              "'%s': missing '}' after block at %ld:%ld", rbrace->filename,
              rbrace->ln, rbrace->cn);
@@ -976,6 +1014,197 @@ fzl_node_t *parse_block(fzl_parser_t *parser)
   return node;
 }
 
+// For-loop parsing
+fzl_node_t *parse_for(fzl_parser_t *parser)
+{
+  fzl_token_t *tok  = consume(parser);
+  fzl_token_t *lpar = consume(parser);
+  if (lpar->type != FZL_TOKTYPE_LPAREN)
+  {
+    snprintf(plast_err, sizeof(plast_err),
+             "'%s': expected '(' after for keyword at %ld:%ld",
+             last_known_tok->filename, last_known_tok->ln, last_known_tok->cn);
+    return NULL;
+  }
+
+  fzl_node_t *start = NULL;
+  if (!is(parser, FZL_TOKTYPE_SEMICOLON))
+  {
+    start = parse_expression(parser);
+    if (!start)
+    {
+      snprintf(plast_err, sizeof(plast_err),
+               "'%s': expected loop init or ';' at %ld:%ld",
+               last_known_tok->filename, last_known_tok->ln,
+               last_known_tok->cn);
+      return NULL;
+    }
+
+    fzl_token_t *sc = consume(parser);
+    if (!sc || sc->type != FZL_TOKTYPE_SEMICOLON)
+    {
+      fzl_freeast(start);
+      snprintf(plast_err, sizeof(plast_err),
+               "'%s': missing ';' after init section at %ld:%ld",
+               last_known_tok->filename, last_known_tok->ln,
+               last_known_tok->cn);
+      return NULL;
+    }
+  }
+  else
+    consume(parser);
+
+  fzl_node_t *condition = NULL;
+  if (!is(parser, FZL_TOKTYPE_SEMICOLON))
+  {
+    condition = parse_expression(parser);
+    if (!condition)
+    {
+      fzl_freeast(start);
+      snprintf(plast_err, sizeof(plast_err),
+               "'%s': expected loop condition or ';' at %ld:%ld",
+               last_known_tok->filename, last_known_tok->ln,
+               last_known_tok->cn);
+      return NULL;
+    }
+
+    fzl_token_t *sc = consume(parser);
+    if (!sc || sc->type != FZL_TOKTYPE_SEMICOLON)
+    {
+      fzl_freeast(start);
+      fzl_freeast(condition);
+      snprintf(plast_err, sizeof(plast_err),
+               "'%s': missing ';' after condition at %ld:%ld",
+               last_known_tok->filename, last_known_tok->ln,
+               last_known_tok->cn);
+      return NULL;
+    }
+  }
+  else
+    consume(parser);
+
+  fzl_node_t *step = NULL;
+  if (!is(parser, FZL_TOKTYPE_RPAREN))
+  {
+    step = parse_expression(parser);
+    if (!step)
+    {
+      fzl_freeast(start);
+      fzl_freeast(condition);
+      snprintf(plast_err, sizeof(plast_err),
+               "'%s': expected loop step end or ')' at %ld:%ld",
+               last_known_tok->filename, last_known_tok->ln,
+               last_known_tok->cn);
+      return NULL;
+    }
+  }
+
+  fzl_token_t *rpar = consume(parser);
+  if (!rpar || rpar->type != FZL_TOKTYPE_RPAREN)
+  {
+    fzl_freeast(start);
+    fzl_freeast(condition);
+    fzl_freeast(step);
+    snprintf(plast_err, sizeof(plast_err),
+             "'%s': missing ')' after loop setup at %ld:%ld",
+             last_known_tok->filename, last_known_tok->ln, last_known_tok->cn);
+    return NULL;
+  }
+
+  fzl_node_t *body = parse_statement(parser);
+  if (!body)
+  {
+    fzl_freeast(start);
+    fzl_freeast(condition);
+    fzl_freeast(step);
+    snprintf(plast_err, sizeof(plast_err),
+             "'%s': missing body of for loop at %ld:%ld",
+             last_known_tok->filename, last_known_tok->ln, last_known_tok->cn);
+    return NULL;
+  }
+
+  fzl_node_t *node = fzl_mknode(FZL_NODETYPE_LOOP, tok);
+  node->loop.init  = start;
+  node->loop.cond  = condition;
+  node->loop.step  = step;
+  node->loop.body  = body;
+
+  return node;
+}
+
+// While-loop parsing
+fzl_node_t *parse_while(fzl_parser_t *parser)
+{
+  fzl_token_t *tok  = consume(parser);
+  fzl_token_t *lpar = consume(parser);
+  if (!lpar || lpar->type != FZL_TOKTYPE_LPAREN)
+  {
+    snprintf(plast_err, sizeof(plast_err),
+             "'%s': missing '(' after while keyword at %ld:%ld",
+             last_known_tok->filename, last_known_tok->ln, last_known_tok->cn);
+    return NULL;
+  }
+
+  fzl_node_t *condition = parse_expression(parser);
+  if (!condition)
+  {
+    snprintf(plast_err, sizeof(plast_err),
+             "'%s': missing condition for 'while' at %ld:%ld",
+             last_known_tok->filename, last_known_tok->ln, last_known_tok->cn);
+    return NULL;
+  }
+
+  fzl_token_t *rpar = consume(parser);
+  if (!rpar || rpar->type != FZL_TOKTYPE_RPAREN)
+  {
+    fzl_freeast(condition);
+    snprintf(plast_err, sizeof(plast_err),
+             "'%s': missing ')' after while loop condition at %ld:%ld",
+             last_known_tok->filename, last_known_tok->ln, last_known_tok->cn);
+    return NULL;
+  }
+
+  fzl_node_t *body = parse_statement(parser);
+  if (!body)
+  {
+    fzl_freeast(condition);
+    snprintf(plast_err, sizeof(plast_err),
+             "'%s': missing while loop body at %ld:%ld",
+             last_known_tok->filename, last_known_tok->ln, last_known_tok->cn);
+    return NULL;
+  }
+
+  fzl_node_t *node = fzl_mknode(FZL_NODETYPE_LOOP, tok);
+  node->loop.cond  = condition;
+  node->loop.body  = body;
+
+  return node;
+}
+
+// `while` and `for` loops
+fzl_node_t *parse_loop(fzl_parser_t *parser)
+{
+  if (!peek(parser))
+    return NULL;
+
+  if (is(parser, FZL_TOKTYPE_FOR))
+    return parse_for(parser);
+  else if (is(parser, FZL_TOKTYPE_WHILE))
+    return parse_while(parser);
+
+  snprintf(plast_err, sizeof(plast_err),
+           "'%s': unknown type of loop at %ld:%ld", last_known_tok->filename,
+           last_known_tok->ln, last_known_tok->cn);
+  return NULL;
+}
+
+// `break` keyword parsing
+fzl_node_t *parse_break(fzl_parser_t *parser)
+{
+  fzl_token_t *tok = consume(parser);
+  return fzl_mknode(FZL_NODETYPE_BREAK, tok);
+}
+
 // Statement parsing
 fzl_node_t *parse_statement(fzl_parser_t *parser)
 {
@@ -994,6 +1223,10 @@ fzl_node_t *parse_statement(fzl_parser_t *parser)
     return parse_if(parser);
   else if (is(parser, FZL_TOKTYPE_LBRACE))
     return parse_block(parser);
+  else if (is(parser, FZL_TOKTYPE_FOR) || is(parser, FZL_TOKTYPE_WHILE))
+    return parse_loop(parser);
+  else if (is(parser, FZL_TOKTYPE_BREAK))
+    res = parse_break(parser);
 
   if (!res)
     res = parse_expression(parser);
@@ -1079,6 +1312,7 @@ void fzl_freeast(fzl_node_t *root)
   {
     switch (root->type)
     {
+      case FZL_NODETYPE_BREAK:
       case FZL_NODETYPE_IDENTIFIER:
       case FZL_NODETYPE_LITERAL:
         break;
@@ -1119,6 +1353,20 @@ void fzl_freeast(fzl_node_t *root)
           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;
+
       case FZL_NODETYPE_ADD:
       case FZL_NODETYPE_SUB:
       case FZL_NODETYPE_MUL:

src/compiler/fzl_reader.c

@@ -73,6 +73,14 @@ fzl_token_t *parse_name(fzl_reader_t *reader)
   if (strcmp(value, "class") == 0)
     tok =
         fzl_mktoken(FZL_TOKTYPE_CLASS, l.line, l.col, value, size, l.filename);
+  else if (strcmp(value, "for") == 0)
+    tok = fzl_mktoken(FZL_TOKTYPE_FOR, l.line, l.col, value, size, l.filename);
+  else if (strcmp(value, "while") == 0)
+    tok =
+        fzl_mktoken(FZL_TOKTYPE_WHILE, l.line, l.col, value, size, l.filename);
+  else if (strcmp(value, "break") == 0)
+    tok =
+        fzl_mktoken(FZL_TOKTYPE_BREAK, l.line, l.col, value, size, l.filename);
   else if (strcmp(value, "new") == 0)
     tok = fzl_mktoken(FZL_TOKTYPE_NEW, l.line, l.col, value, size, l.filename);
   else if (strcmp(value, "fn") == 0)

src/compiler/fzl_walker.c

@@ -14,6 +14,9 @@
 #include <stdlib.h>
 #include <string.h>
 
+extern bool is_infinite_loop(fzl_walker_t *walker, fzl_node_t *node, size_t ls,
+                             size_t le);
+
 char *null_name = "<null>";
 char wlast_err[256];
 
@@ -200,6 +203,145 @@ fzl_walk_res_t walk(fzl_walker_t *walker, fzl_node_t *node)
   {
     switch (node->type)
     {
+      case FZL_NODETYPE_BREAK:
+      {
+        fzl_walk_ctx_t *ctx = walker->ctx;
+        while (ctx)
+        {
+          if (ctx->type == FZL_WALK_CTX_TYPE_LOOP)
+            break;
+
+          ctx = ctx->parent;
+        }
+
+        if (!ctx || ctx->type != FZL_WALK_CTX_TYPE_LOOP)
+        {
+          snprintf(wlast_err, sizeof(wlast_err),
+                   "'%s': usage of 'break' outsude the loop at %ld:%ld",
+                   node->token->filename, node->token->ln, node->token->cn);
+          return (fzl_walk_res_t){.error = true, .error_msg = wlast_err};
+        }
+
+        for (size_t i = walker->sym_top - 1; i > ctx->initial_env_lvl + 1; i--)
+          push_op(walker, FZL_OPCODE_RM_ENVTABLE);
+
+        if (ctx->breaks_remainder <= ctx->breaks_count)
+        {
+          ctx->breaks_remainder *= 2;
+          ctx->breaks =
+              realloc(ctx->breaks, ctx->breaks_remainder * sizeof(size_t));
+        }
+
+        push_op(walker, FZL_OPCODE_JMP);
+        ctx->breaks[ctx->breaks_count++] = walker->op_count;
+        push_word(walker, 0);
+
+        current_res = (fzl_walk_res_t){.type = FZL_TYPE_NULL, .error = false};
+        break;
+      }
+
+      // NOTE: add new levels for infinite loop check:
+      //  1. Step direction (f.e. `for (; i > 5; i = i - 1)`)
+      case FZL_NODETYPE_LOOP:
+      {
+        fzl_walk_ctx_t *newctx = nest_ctx(walker, FZL_WALK_CTX_TYPE_LOOP);
+        if (!newctx)
+        {
+          snprintf(wlast_err, sizeof(wlast_err), "failed to nest context");
+          return (fzl_walk_res_t){.error = true, .error_msg = wlast_err};
+        }
+
+        newctx->initial_env_lvl  = walker->sym_top - 1;
+        newctx->breaks_count     = 0;
+        newctx->breaks_remainder = 2;
+        newctx->breaks = malloc(newctx->breaks_remainder * sizeof(size_t));
+
+        push_op(walker, FZL_OPCODE_MK_ENVTABLE);
+        walker->syms[walker->sym_top++] = fzl_mksymt();
+        size_t loop_begin_ip            = walker->op_count;
+
+        if (node->loop.init)
+        {
+          fzl_walk_res_t res = walk(walker, node->loop.init);
+          if (res.error)
+          {
+            free(newctx->breaks);
+            return res;
+          }
+        }
+
+        size_t start_ip = walker->op_count;
+        if (node->loop.cond)
+        {
+          fzl_walk_res_t res = walk(walker, node->loop.cond);
+          if (res.error)
+          {
+            free(newctx->breaks);
+            return res;
+          }
+        }
+        else
+        {
+          push_op(walker, FZL_OPCODE_PUSHNUM);
+          push_word(walker, 1);
+        }
+
+        push_op(walker, FZL_OPCODE_JZ);
+        newctx->breaks[newctx->breaks_count++] = walker->op_count;
+        push_word(walker, 0);
+
+        fzl_walk_res_t loop_body_res = walk(walker, node->loop.body);
+        if (loop_body_res.error)
+        {
+          free(newctx->breaks);
+          return loop_body_res;
+        }
+
+        if (node->loop.step)
+        {
+          fzl_walk_res_t res = walk(walker, node->loop.step);
+          if (res.error)
+          {
+            free(newctx->breaks);
+            return res;
+          }
+        }
+
+        push_op(walker, FZL_OPCODE_JMP);
+        push_word(walker, start_ip);
+
+        // backpatch `break`s
+        for (size_t i = 0; i < newctx->breaks_count; i++)
+          walker->ops[newctx->breaks[i]] = walker->op_count;
+
+        push_op(walker, FZL_OPCODE_RM_ENVTABLE);
+
+        bool is_infinite =
+            is_infinite_loop(walker, node, loop_begin_ip, walker->op_count - 2);
+        if (is_infinite)
+        {
+          free(newctx->breaks);
+          snprintf(wlast_err, sizeof(wlast_err),
+                   "'%s': infinite loop detected at %ld:%ld",
+                   node->token->filename, node->token->ln, node->token->cn);
+          return (fzl_walk_res_t){.error = true, .error_msg = wlast_err};
+        }
+
+        for (size_t i = walker->sym_top - 1; i > newctx->initial_env_lvl; i--)
+          fzl_freesymt(walker->syms[--walker->sym_top]);
+
+        free(newctx->breaks);
+        if (!fin_ctx(walker))
+        {
+          snprintf(wlast_err, sizeof(wlast_err),
+                   "failed to finish loop context");
+          return (fzl_walk_res_t){.error = true, .error_msg = wlast_err};
+        }
+
+        current_res = (fzl_walk_res_t){.type = FZL_TYPE_NULL, .error = false};
+        break;
+      }
+
       case FZL_NODETYPE_CLASS:
       {
         fzl_walk_ctx_t *newctx = nest_ctx(walker, FZL_WALK_CTX_TYPE_CLASS);
@@ -461,7 +603,16 @@ fzl_walk_res_t walk(fzl_walker_t *walker, fzl_node_t *node)
 
       case FZL_NODETYPE_RETURN:
       {
-        if (!walker->ctx || walker->ctx->type != FZL_WALK_CTX_TYPE_FN)
+        fzl_walk_ctx_t *ctx = walker->ctx;
+        while (ctx)
+        {
+          if (ctx && ctx->type == FZL_WALK_CTX_TYPE_FN)
+            break;
+
+          ctx = ctx->parent;
+        }
+
+        if (!ctx || ctx->type != FZL_WALK_CTX_TYPE_FN)
         {
           snprintf(
               wlast_err, sizeof(wlast_err),
@@ -731,6 +882,7 @@ fzl_walk_res_t walk(fzl_walker_t *walker, fzl_node_t *node)
           }
         fzl_freesymt(walker->syms[--walker->sym_top]);
         push_op(walker, FZL_OPCODE_RM_ENVTABLE);
+        current_res = (fzl_walk_res_t){.type = FZL_TYPE_NULL, .error = false};
         break;
 
       case FZL_NODETYPE_CALL:
@@ -1056,9 +1208,19 @@ fzl_walk_res_t walk(fzl_walker_t *walker, fzl_node_t *node)
         if (res != FZL_SYMTABLE_RESULT_OK)
         {
           fzl_token_t *tok = node->var.identifier->token;
+          if (res == FZL_SYMTABLE_RESULT_EXISTS)
+          {
+            snprintf(wlast_err, sizeof(wlast_err),
+                     "'%s': cannot redefine '%s' at %ld:%ld", tok->filename,
+                     (char *)tok->value, tok->ln, tok->cn);
+          }
+          else
+          {
             snprintf(wlast_err, sizeof(wlast_err),
                      "'%s': cannot store '%s' at %ld:%ld", tok->filename,
                      (char *)tok->value, tok->ln, tok->cn);
+          }
+
           return (fzl_walk_res_t){.error = true, .error_msg = wlast_err};
         }
 
@@ -1225,6 +1387,11 @@ int fzl_walk(fzl_walker_t *walker)
   push_op(walker, FZL_OPCODE_RM_ENVTABLE);
 
   fin_ctx(walker);
+  if (walker->ctx)
+  {
+    while (walker->ctx)
+      fin_ctx(walker);
+  }
 
   if (result.error && !wlast_err[0])
     snprintf(wlast_err, sizeof(wlast_err), "%s", result.error_msg);

src/compiler/main.c

@@ -96,11 +96,21 @@ int main(int argc, char **argv)
   }
 
   fzl_parser_t *parser = fzl_mkparser(rd->first);
+  if (!parser)
+  {
+    printf("%sError%s: failed to allocate writer\n", FZL_CERROR, FZL_CRST);
+    fzl_freeoptions(opts);
+    fzl_freereader(rd);
+    fzl_freelinked(linked);
+    return -1;
+  }
+
   result = fzl_parse(parser);
   if (result != 0)
   {
     printf("%sError%s: %s\n", FZL_CERROR, FZL_CRST, fzl_parser_geterror());
     fzl_freeoptions(opts);
+    fzl_freeast(parser->root);
     fzl_freeparser(parser);
     fzl_freereader(rd);
     fzl_freelinked(linked);
@@ -116,12 +126,24 @@ int main(int argc, char **argv)
   }
 
   fzl_walker_t *walker = fzl_mkwalker(parser->root);
+  if (!walker)
+  {
+    printf("%sError%s: failed to allocate writer\n", FZL_CERROR, FZL_CRST);
+    fzl_freeoptions(opts);
+    fzl_freeast(parser->root);
+    fzl_freeparser(parser);
+    fzl_freereader(rd);
+    fzl_freelinked(linked);
+    return -1;
+  }
+
   result = fzl_walk(walker);
   if (result != 0)
   {
     printf("%sError%s: %s\n", FZL_CERROR, FZL_CRST, fzl_walker_geterror());
     fzl_freeoptions(opts);
     fzl_freewalker(walker);
+    fzl_freeast(parser->root);
     fzl_freeparser(parser);
     fzl_freereader(rd);
     fzl_freelinked(linked);
@@ -162,6 +184,18 @@ int main(int argc, char **argv)
   }
 
   fzl_writer_t *writer = fzl_mkwriter(outpath);
+  if (!writer)
+  {
+    printf("%sError%s: failed to allocate writer\n", FZL_CERROR, FZL_CRST);
+    fzl_freeoptions(opts);
+    fzl_freewalker(walker);
+    fzl_freeast(parser->root);
+    fzl_freeparser(parser);
+    fzl_freereader(rd);
+    fzl_freelinked(linked);
+    return -1;
+  }
+
   result = fzl_write(writer, walker);
   if (result != 0)
   {
@@ -169,6 +203,7 @@ int main(int argc, char **argv)
     fzl_freeoptions(opts);
     fzl_freewriter(writer);
     fzl_freewalker(walker);
+    fzl_freeast(parser->root);
     fzl_freeparser(parser);
     fzl_freereader(rd);
     fzl_freelinked(linked);

src/vm/fzl_vm.c

@@ -4,6 +4,7 @@
 #include <common/fzl_value.h>
 #include <compiler/utils/fzl_const_pool.h>
 #include <stdbool.h>
+#include <stddef.h>
 #include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -13,6 +14,11 @@
 #include <vm/fzl_vm_object.h>
 
 char last_err[256];
+size_t last_jmp_ip = 0;
+
+// NOTE: add `--max-iter` option for limit
+size_t max_iter_limit    = 100000;
+size_t total_jmp_on_same = 0;
 
 static char *expect_hdr = "FZL\0\1";
 
@@ -667,7 +673,22 @@ int fzl_vm_run(fzl_vm_t *vm)
           return -1;
         }
         uint64_t jmp_ip = vm->ops[++vm->ip];
+        if (jmp_ip == last_jmp_ip)
+          total_jmp_on_same++;
+        else
+          total_jmp_on_same = 0;
+
+        if (total_jmp_on_same > max_iter_limit)
+        {
+          snprintf(last_err, sizeof(last_err),
+                   "runtime error - exceeded max loop jumps (infinite loop?)\n"
+                   "If you thinks there's mistake, change jumps limit with "
+                   "--max-iter=N");
+          return -1;
+        }
+
         vm->ip      = jmp_ip - 1;
+        last_jmp_ip = jmp_ip;
         break;
       }
 

tests/programs/neg1_infinite_for.fzs

@@ -0,0 +1,3 @@
+for (int i = 0; i < 5; i = i + 0)
+{}
+

tests/programs/neg_infinite_while.fzs

@@ -0,0 +1,3 @@
+while (true)
+{}
+

tests/programs/neg_missing_operand.fzs

@@ -0,0 +1,2 @@
+printline(1 + );
+

tests/programs/neg_missing_semicolon.fzs

@@ -0,0 +1,3 @@
+int value = 42
+printline(value);
+

tests/programs/neg_unclosed_block.fzs

@@ -0,0 +1,4 @@
+if (true)
+{
+  printline("missing closing brace");
+

tests/programs/neg_unterminated_string.fzs

@@ -0,0 +1,2 @@
+printline("unterminated string);
+

tests/programs/pos_arithmetic.fzs

@@ -0,0 +1,7 @@
+// Arithmetic precedence and operators.
+printline(2 + 2 * 2);
+printline(-1 + 1);
+printline(2 ^ 2);
+printline(4 % 2);
+printline(10 / 2);
+

tests/programs/pos_class.fzs

@@ -0,0 +1,25 @@
+class Point
+{
+  int x;
+  int y;
+
+  fn move(int dx, int dy)
+  {
+    this.x = this.x + dx;
+    this.y = this.y + dy;
+  }
+}
+
+Point point = new Point;
+point.x = 1;
+point.y = 2;
+point.move(9, 8);
+
+if (point.x == 10 && point.y == 10)
+  printline("class method passed");
+else
+{
+  printline("class method failed");
+  exit(1);
+}
+

tests/programs/pos_comments_strings.fzs

@@ -0,0 +1,5 @@
+// Line comments are ignored by the parser.
+printline('single-quoted string');;;;;
+printline("");
+printline("double-quoted string");
+

tests/programs/pos_conditions.fzs

@@ -0,0 +1,21 @@
+bool flag = true;
+
+if (!flag)
+{
+  printline("unexpected false");
+  exit(1);
+}
+else if (2 + 2 >= 4)
+{
+  printline("condition passed");
+}
+else
+{
+  printline("unexpected branch");
+  exit(1);
+}
+
+{
+  printline("standalone block");
+}
+

tests/programs/pos_functions.fzs

@@ -0,0 +1,21 @@
+fn fib(int n) int
+{
+  if (n <= 1)
+    return n;
+
+  return fib(n - 1) + fib(n - 2);
+}
+
+fn sum(uint a, uint b) uint
+{
+  return a + b;
+}
+
+if (fib(7) == 13 && sum(2, 2) == 4)
+  printline("functions passed");
+else
+{
+  printline("functions failed");
+  exit(1);
+}
+

tests/programs/pos_loop_with_break.fzs

@@ -0,0 +1,7 @@
+int i = 0;
+
+for (;;)
+{
+  break;
+}
+

tests/programs/pos_loops.fzs

@@ -0,0 +1,27 @@
+for (int i = 0; i < 10; i = i + 1)
+  printline("check");
+
+int i = 0;
+for (i = 0; i <= 5; i = i + 1)
+{
+  printline("i is:");
+  printline(i);
+}
+
+if (i < 5)
+{
+  printline("external declared `i` != 5");
+  exit(1);
+}
+
+while (i > 0)
+{
+  i = i - 1;
+}
+
+if (i > 0)
+{
+  printline("decreased in while loop `i` > 0");
+  exit(1);
+}
+

tests/programs/pos_null.fzs

@@ -0,0 +1,23 @@
+class Item
+{
+  int value;
+}
+
+fn maybe_item(bool create) Item
+{
+  if (create)
+    return new Item;
+
+  return null;
+}
+
+Item empty = maybe_item(false);
+Item present = maybe_item(true);
+if (empty == null && present != null)
+  printline("null handling passed");
+else
+{
+  printline("null handling failed");
+  exit(1);
+}
+

tests/programs/pos_variables.fzs

@@ -0,0 +1,13 @@
+uint work_it = 21 * 2 ^ 2;
+int make_it = 10;
+u64 do_it;
+do_it = 15;
+char make_us;
+str floyd = "hello, Pink Floyd!";
+bool flag = true;
+
+printline(work_it);
+printline(make_it + do_it);
+printline(floyd);
+printline(flag);
+