Add exported variable (only functions for now), export main func, start execution from main func

18 files changed, 394 insertions, 216 deletions

diff --git a/doc/Documentation.md b/doc/Documentation.md
index 79e81aa..8b2133e 100644
--- a/doc/Documentation.md
+++ b/doc/Documentation.md
@@ -15,7 +15,7 @@ Instructions can be in 7 different formats:
 6.1 Opcode(u8) + register(i8) + offset(i16)\
 6.2 Opcode(u8) + register(i8) + intermediate(u16)\
 6.3 Opcode(u8) + register(i8) + data(u16)\
-6.4 Opcode(u8) + num_param_reg(u8) + num_local_var_reg(u16)
+6.4 Opcode(u8) + flags(u8) + num_local_var_reg(u16)
 7. 5 bytes: Opcode(u8) + index(u16) + num_args(u8) + register(i8)
 ## Registers
 Registers have a range of 128. Local variables start from register 0 and increment while parameters start from -1
@@ -29,7 +29,7 @@ and writing it to a file, which is an IO bottlenecked operation and it won't ben
 and may even lose performance because of it.
 
 # Bytecode
-The layout of the full bytecode is: Header (Intermediates Strings Functions External_Functions Instructions)*
+The layout of the full bytecode is: Header (Intermediates Strings Functions External_Functions Exported_Functions Instructions)*
 
 # Bytecode header
 ## Header layout
@@ -90,6 +90,22 @@ The versions in the header only changes for every release, not every change.
 |u8  |name_len|The length of the external function name, in bytes. Excluding the null-terminate character.          |
 |u8* |name    |The name of the external function, where the size is defined by @name_len. Names are null-terminated.|
 
+# Bytecode exported functions
+## Exported functions layout
+|Type             |Field             |Description                                                                              |
+|-----------------|------------------|-----------------------------------------------------------------------------------------|
+|u16              |num_export_func   |The number of exported functions.                                                        |
+|u32              |export_funcs_size |The size of the exported functions section, in bytes.                                    |
+|Exported function|Exported functions|Multiple exported functions, where the number of functions is defined by @num_export_func|
+
+## Exported function
+|Type|Field             |Description                                                                                                               |
+|----|------------------|--------------------------------------------------------------------------------------------------------------------------|
+|u32 |instruction_offset|The offset in the instruction data where the exported function is defined. Is always 0 until the program has been started.|
+|u8  |num_args          |The number of arguments the functions has.                                                                                |
+|u8  |name_len          |The length of the exported function name, in bytes. Excluding the null-terminate character.                               |
+|u8* |name              |The name of the exported function, where the size is defined by @name_len. Names are null-terminated.                     |
+
 # Bytecode instructions
 ## Instructions layout
 |Type       |Field            |Description                                                                |
diff --git a/executor/executor.h b/executor/executor.h
index 979784b..df6c0d8 100644
--- a/executor/executor.h
+++ b/executor/executor.h
@@ -18,7 +18,8 @@ typedef struct amal_executor amal_executor;
 
 CHECK_RESULT int amal_executor_init(amal_executor **self);
 void amal_executor_deinit(amal_executor *self);
-CHECK_RESULT int amal_executor_run(amal_executor *self);
+CHECK_RESULT int amal_executor_run(amal_executor *self, u32 offset);
+u32 amal_exec_get_code_offset(amal_executor *self);
 
 /* These functions are called for every file in the program. Every file has its own list of strings, intermediates, functions and external functions */
 CHECK_RESULT int amal_executor_instructions_start(amal_executor *self, u16 num_functions);
diff --git a/executor/x86_64/asm.c b/executor/x86_64/asm.c
index c741f15..f2bb801 100644
--- a/executor/x86_64/asm.c
+++ b/executor/x86_64/asm.c
@@ -210,7 +210,7 @@ static void asm_print_code_hex(Asm *self) {
 }
 #endif
 
-int asm_execute(Asm *self) {
+int asm_execute(Asm *self, u32 offset) {
     void (*func)();
     if(mprotect(self->code, self->allocated_size, PROT_READ | PROT_EXEC) != 0)
         return -errno;
@@ -218,7 +218,7 @@ int asm_execute(Asm *self) {
     /*asm_print_code_hex(self);*/
 
     /* TODO: Verify if this is valid on all platforms. According to ISO C standard it isn't? */
-    *(void**)(&func) = self->code;
+    *(void**)(&func) = self->code + offset;
     func();
     return 0;
 }
diff --git a/executor/x86_64/asm.h b/executor/x86_64/asm.h
index 51f2d84..ace1ecf 100644
--- a/executor/x86_64/asm.h
+++ b/executor/x86_64/asm.h
@@ -49,7 +49,7 @@ void asm_deinit(Asm *self);
 
 usize asm_get_size(Asm *self);
 
-CHECK_RESULT int asm_execute(Asm *self);
+CHECK_RESULT int asm_execute(Asm *self, u32 offset);
 
 CHECK_RESULT int asm_nop(Asm *self);
 
diff --git a/executor/x86_64/executor.c b/executor/x86_64/executor.c
index fbe227a..335790a 100644
--- a/executor/x86_64/executor.c
+++ b/executor/x86_64/executor.c
@@ -64,9 +64,14 @@ void amal_executor_deinit(amal_executor *self) {
     am_free(impl);
 }
 
-int amal_executor_run(amal_executor *self) {
+int amal_executor_run(amal_executor *self, u32 offset) {
     IMPL
-    return asm_execute(&impl->asm);
+    return asm_execute(&impl->asm, offset);
+}
+
+u32 amal_exec_get_code_offset(amal_executor *self) {
+    IMPL
+    return asm_get_size(&impl->asm);
 }
 
 int amal_executor_instructions_start(amal_executor *self, u16 num_functions) {
diff --git a/include/bytecode/bytecode.h b/include/bytecode/bytecode.h
index 1e4c35d..64b54b4 100644
--- a/include/bytecode/bytecode.h
+++ b/include/bytecode/bytecode.h
@@ -25,7 +25,7 @@
     6.1 Opcode(u8) + register(i8) + offset(i16)\
     6.2 Opcode(u8) + register(i8) + intermediate(u16)\
     6.3 Opcode(u8) + register(i8) + data(u16)\
-    6.4 Opcode(u8) + num_param_reg(u8) + num_local_var_reg(u16)
+    6.4 Opcode(u8) + flags(u8) + num_local_var_reg(u16)
     7. 5 bytes: Opcode(u8) + index(u16) + num_args(u8) + register(i8)
     # Registers
     Registers have a range of 128. Local variables start from register 0 and increment while parameters start from -1
@@ -33,30 +33,42 @@
 */
 typedef enum {
     AMAL_OP_NOP,         /* No operation (do nothing). This can be used for patching code */
-    AMAL_OP_SETZ,        /* setz reg                                     - Set register value to 0 */
-    AMAL_OP_MOV,         /* mov dst, src                                 - Move src register to dst register */
-    AMAL_OP_MOVI,        /* movi dst, src                                - Move src intermediate to dst register */
-    AMAL_OP_MOVD,        /* movd dst, src                                - Move src data to dst register */
-    AMAL_OP_ADD,         /* add dst, reg1, reg2                          - Add reg1 and reg2 and put the result in dst */
-    AMAL_OP_SUB,         /* sub dst, reg1, reg2                          - Substract reg2 from reg1 and put the result in dst */
-    AMAL_OP_IMUL,        /* imul dst, reg1, reg2                         - Signed multiplication */
-    AMAL_OP_MUL,         /* mul dst, reg1, reg2                          - Unsigned multiplication */
-    AMAL_OP_IDIV,        /* idiv dst, reg1, reg2                         - Signed division */
-    AMAL_OP_DIV,         /* div dst, reg1, reg2                          - Unsigned division */
-    AMAL_OP_PUSH,        /* push reg                                     - Push register onto stack */
-    AMAL_OP_PUSHI,       /* pushi int                                    - Push intermediate onto stack */
-    AMAL_OP_PUSHD,       /* pushd data                                   - Push data onto stack */
-    AMAL_OP_CALL,        /* call fi, num_args, dst                       - Call a function using function index (fi) and num_args arguments. The result is stored in register dst. fi is u16 and num_args is u8 */
-    AMAL_OP_CALLR,       /* callr reg, num_args                          - Call a function using a register. Used for function pointers. num_args is u8 */
-    AMAL_OP_CALLE,       /* calle efi, num_args, dst                     - Call an extern function using extern function index (efi) and num_args arguments. The result is stored in register dst. efi is u16 and num_args is u8 */
-    AMAL_OP_CMP,         /* cmp dst, reg1, reg2                          - Set dst to 1 if reg1 equals reg2, otherwise set it to 0 */
-    AMAL_OP_JZ,          /* jz reg, offset                               - Jump to offset if reg is zero. offset is i16 */
-    AMAL_OP_JMP,         /* jmp offset                                   - Unconditional jump to offset. offset is i16 */
-    AMAL_OP_RET,         /* ret reg                                      - Return from the function with reg result */
-    AMAL_OP_FUNC_START,  /* func_start num_param_reg, num_local_var_reg  - Start of a function which has num_param_reg parameter registers allocated and num_local_var_reg local variable registers allocated. num_param_reg is u8 and num_local_var_reg is u16 */
-    AMAL_OP_FUNC_END     /* func_end                                     - End of a function. Implementation should do a ret here */
+    AMAL_OP_SETZ,        /* setz reg                             - Set register value to 0 */
+    AMAL_OP_MOV,         /* mov dst, src                         - Move src register to dst register */
+    AMAL_OP_MOVI,        /* movi dst, src                        - Move src intermediate to dst register */
+    AMAL_OP_MOVD,        /* movd dst, src                        - Move src data to dst register */
+    AMAL_OP_ADD,         /* add dst, reg1, reg2                  - Add reg1 and reg2 and put the result in dst */
+    AMAL_OP_SUB,         /* sub dst, reg1, reg2                  - Substract reg2 from reg1 and put the result in dst */
+    AMAL_OP_IMUL,        /* imul dst, reg1, reg2                 - Signed multiplication */
+    AMAL_OP_MUL,         /* mul dst, reg1, reg2                  - Unsigned multiplication */
+    AMAL_OP_IDIV,        /* idiv dst, reg1, reg2                 - Signed division */
+    AMAL_OP_DIV,         /* div dst, reg1, reg2                  - Unsigned division */
+    AMAL_OP_PUSH,        /* push reg                             - Push register onto stack */
+    AMAL_OP_PUSHI,       /* pushi int                            - Push intermediate onto stack */
+    AMAL_OP_PUSHD,       /* pushd data                           - Push data onto stack */
+    AMAL_OP_CALL,        /* call fi, num_args, dst               - Call a function using function index (fi) and num_args arguments. The result is stored in register dst. fi is u16 and num_args is u8 */
+    AMAL_OP_CALLR,       /* callr reg, num_args                  - Call a function using a register. Used for function pointers. num_args is u8 */
+    AMAL_OP_CALLE,       /* calle efi, num_args, dst             - Call an extern function using extern function index (efi) and num_args arguments. The result is stored in register dst. efi is u16 and num_args is u8 */
+    AMAL_OP_CMP,         /* cmp dst, reg1, reg2                  - Set dst to 1 if reg1 equals reg2, otherwise set it to 0 */
+    AMAL_OP_JZ,          /* jz reg, offset                       - Jump to offset if reg is zero. offset is i16 */
+    AMAL_OP_JMP,         /* jmp offset                           - Unconditional jump to offset. offset is i16 */
+    AMAL_OP_RET,         /* ret reg                              - Return from the function with reg result */
+    AMAL_OP_FUNC_START,  /* func_start flags, num_local_var_reg  - Start of a function which has @num_local_var_reg local variable registers allocated and has the flag @flag. @flag is u8 and @num_local_var_reg is u16 */
+    AMAL_OP_FUNC_END     /* func_end                             - End of a function. Implementation should do a ret here */
 } AmalOpcode;
 
+#define AMAL_BYTECODE_MAGIC_NUMBER (u32)0xdec05eba
+#define AMAL_BYTECODE_MAJOR_VERSION 1
+#define AMAL_BYTECODE_MINOR_VERSION 0
+#define AMAL_BYTECODE_PATCH_VERSION 0
+
+#define AMAL_BYTECODE_NUM_REGISTERS 256
+
+typedef enum {
+    FUNC_FLAG_NONE       = 0,
+    FUNC_FLAG_EXPORTED   = (1 << 1)
+} amal_func_flag;
+
 typedef u8 AmalOpcodeType;
 
 typedef struct {
@@ -71,6 +83,8 @@ typedef struct {
 
 CHECK_RESULT int bytecode_init(Bytecode *self, ArenaAllocator *allocator);
 
+CHECK_RESULT int buffer_append_header(Buffer *program_data);
+
 /* longjump to self->env on failure */
 void generate_bytecode_from_ssa(BytecodeCompilerContext *self);
 
diff --git a/include/program.h b/include/program.h
index 075bfca..e3a4ac9 100644
--- a/include/program.h
+++ b/include/program.h
@@ -31,13 +31,10 @@
 #define AMAL_PROGRAM_INSTRUCTION_INVALID_EXTERN_FUNC_INDEX -19
 #define AMAL_PROGRAM_NO_SUCH_EXTERNAL_FUNCTION -20
 #define AMAL_PROGRAM_EXTERN_FUNC_ALREADY_EXISTS -21
-
-#define AMAL_PROGRAM_MAGIC_NUMBER (u32)0xdec05eba
-#define AMAL_PROGRAM_MAJOR_VERSION 1
-#define AMAL_PROGRAM_MINOR_VERSION 0
-#define AMAL_PROGRAM_PATCH_VERSION 0
-
-#define AMAL_PROGRAM_NUM_REGISTERS 256
+#define AMAL_PROGRAM_INVALID_EXPORTED_FUNCTIONS -22
+#define AMAL_PROGRAM_INVALID_EXPORTED_FUNCTIONS_SIZE -23
+#define AMAL_PROGRAM_INSTRUCTION_INVALID_EXPORTED_FUNC_INDEX -24
+#define AMAL_PROGRAM_NO_MAIN_FUNC -25
 
 #define AMAL_PROGRAM_ARGS_SIZE_VARARGS -1
 
@@ -53,12 +50,17 @@ typedef struct {
     u8 *intermediates_start;  /* Reference inside @data */
     u8 *strings_start;        /* Reference inside @data */
     u8 *extern_funcs_start;   /* Reference inside @data */
+    u8 *exported_funcs;       /* Reference inside @data */
+    u8 *exported_funcs_end;   /* Reference inside @data */
+
     usize read_index;
+    u32 main_func_instruction_offset;
 
     u16 num_intermediates;
     u16 num_strings;
     u16 num_functions;
     u16 num_extern_functions;
+    u16 num_exported_functions;
 
     ArenaAllocator allocator; /* Owned. Used by @extern_funcs_map */
     HashMapType(BufferView, ProgramExternFunc) extern_funcs_map;
diff --git a/include/ssa/ssa.h b/include/ssa/ssa.h
index b2c8065..ed147bf 100644
--- a/include/ssa/ssa.h
+++ b/include/ssa/ssa.h
@@ -49,11 +49,17 @@ typedef struct {
     BufferView name;
 } SsaExternFunc;
 
+typedef struct {
+    FunctionSignature *func_sig;
+    BufferView name;
+} SsaExportFunc;
+
 typedef i16 JumpOffset;
 typedef i16 SsaRegister;
 typedef u16 SsaIntermediateIndex;
 typedef u16 SsaStringIndex;
 typedef u16 SsaExternFuncIndex;
+typedef u16 SsaExportFuncIndex;
 typedef u16 SsaFuncIndex;
 
 typedef struct {
@@ -64,9 +70,11 @@ typedef struct {
     Buffer/*BufferView*/ strings;
     HashMapType(BufferView, SsaExternFuncIndex) extern_funcs_map;
     Buffer/*SsaExternFunc*/ extern_funcs;
+    Buffer/*SsaExportFunc*/ export_funcs;
     SsaIntermediateIndex intermediate_counter;
     SsaStringIndex string_counter;
     SsaExternFuncIndex extern_func_counter;
+    SsaExportFuncIndex export_func_counter;
     SsaRegister reg_counter;
     SsaRegister param_counter;
     SsaFuncIndex func_counter;
@@ -85,8 +93,7 @@ typedef struct {
 } SsaInsForm2;
 
 typedef struct {
-    SsaFuncIndex func_index;
-    u16 num_params_regs;
+    u8 flags;
     u16 num_local_vars_regs;
 } SsaInsFuncStart;
 
diff --git a/include/tokenizer.h b/include/tokenizer.h
index 16123cc..57ed9de 100644
--- a/include/tokenizer.h
+++ b/include/tokenizer.h
@@ -38,6 +38,7 @@ typedef enum {
     TOK_ELSE,
     TOK_WHILE,
     TOK_EXTERN,
+    TOK_EXPORT,
     TOK_RETURN
 } Token;
 
diff --git a/src/bytecode/bytecode.c b/src/bytecode/bytecode.c
index 80cc95b..fe3dc0f 100644
--- a/src/bytecode/bytecode.c
+++ b/src/bytecode/bytecode.c
@@ -23,6 +23,36 @@ int bytecode_init(Bytecode *self, ArenaAllocator *allocator) {
     return buffer_init(&self->data, allocator);
 }
 
+/*doc(Bytecode)
+The layout of the full bytecode is: Header (Intermediates Strings Functions External_Functions Exported_Functions Instructions)*
+*/
+
+CHECK_RESULT int buffer_append_header(Buffer *program_data) {
+    /*doc(Bytecode header)
+        # Header layout
+        |Type|Field        |Description                                                                 |
+        |----|-------------|----------------------------------------------------------------------------|
+        |u32 |Magic number |The magic number used to identify an amalgam bytecode file.                 |
+        |u8  |Major version|The major version of the bytecode. Updates in this is a breaking change.    |
+        |u8  |Minor version|The minor version of the bytecode. Updates in this are backwards compatible.|
+        |u8  |Patch version|The patch version of the bytecode. Updates in this are only minor bug fixes.|
+
+        The versions in the header only changes for every release, not every change.
+    */
+
+    const u32 magic_number = AMAL_BYTECODE_MAGIC_NUMBER;
+    const u8 major_version = AMAL_BYTECODE_MAJOR_VERSION;
+    const u8 minor_version = AMAL_BYTECODE_MINOR_VERSION;
+    const u8 patch_version = AMAL_BYTECODE_PATCH_VERSION;
+
+    return_if_error(buffer_append(program_data, &magic_number, 4));
+    return_if_error(buffer_append(program_data, &major_version, 1));
+    return_if_error(buffer_append(program_data, &minor_version, 1));
+    return_if_error(buffer_append(program_data, &patch_version, 1));
+
+    return 0;
+}
+
 static CHECK_RESULT usize ssa_extract_data(u8 *instruction_data, void *result, usize size) {
     am_memcpy(result, instruction_data, size);
     return size;
@@ -43,18 +73,12 @@ static void add_intermediates(BytecodeCompilerContext *self) {
         |u64 |Value|The type of the value depends on the value of @Type.|
     */
 
-    Ssa *ssa;
-    Buffer *instructions;
-    SsaNumber *intermediate;
-    SsaNumber *intermediates_end;
-    u32 intemediates_size;
-
-    ssa = self->parser->ssa;
-    instructions = &self->bytecode.data;
-    intermediate = buffer_begin(&ssa->intermediates);
-    intermediates_end = buffer_end(&ssa->intermediates);
+    Ssa *ssa = self->parser->ssa;
+    Buffer *instructions = &self->bytecode.data;
+    SsaNumber *intermediate = buffer_begin(&ssa->intermediates);
+    SsaNumber *intermediates_end = buffer_end(&ssa->intermediates);
 
-    intemediates_size = (sizeof(u8) + sizeof(u64)) * buffer_get_size(&ssa->intermediates, SsaNumber);
+    u32 intemediates_size = (sizeof(u8) + sizeof(u64)) * buffer_get_size(&ssa->intermediates, SsaNumber);
     throw_if_error(buffer_expand(instructions, sizeof(u32) + intemediates_size));
     throw_if_error(buffer_append(instructions, &intemediates_size, sizeof(u32)));
     for(; intermediate != intermediates_end; ++intermediate) {
@@ -80,17 +104,11 @@ static void add_strings(BytecodeCompilerContext *self) {
         |u8* |Data|The data of the string, where the size is defined by @Size. Strings are null-terminated.|
     */
 
-    Ssa *ssa;
-    Buffer *instructions;
-    BufferView *string;
-    BufferView *strings_end;
-    u32 strings_size;
-
-    ssa = self->parser->ssa;
-    instructions = &self->bytecode.data;
-    string = buffer_begin(&ssa->strings);
-    strings_end = buffer_end(&ssa->strings);
-    strings_size = 0;
+    Ssa *ssa = self->parser->ssa;
+    Buffer *instructions = &self->bytecode.data;
+    BufferView *string = buffer_begin(&ssa->strings);
+    BufferView *strings_end = buffer_end(&ssa->strings);
+    u32 strings_size = 0;
 
     for(; string != strings_end; ++string) {
         strings_size += sizeof(u16) + string->size + 1; /* +1 for null-termination of string */
@@ -136,17 +154,11 @@ static void add_extern_functions(BytecodeCompilerContext *self) {
         |u8  |name_len|The length of the external function name, in bytes. Excluding the null-terminate character.          |
         |u8* |name    |The name of the external function, where the size is defined by @name_len. Names are null-terminated.|
     */
-
-    Ssa *ssa;
-    Buffer *instructions;
-    SsaExternFunc *extern_func, *extern_func_end;
-    u32 extern_funcs_size;
-
-    ssa = self->parser->ssa;
-    instructions = &self->bytecode.data;
-    extern_func = buffer_begin(&ssa->extern_funcs);
-    extern_func_end = buffer_end(&ssa->extern_funcs);
-    extern_funcs_size = 0;
+    Ssa *ssa = self->parser->ssa;
+    Buffer *instructions = &self->bytecode.data;
+    SsaExternFunc *extern_func = buffer_begin(&ssa->extern_funcs);
+    SsaExternFunc *extern_func_end = buffer_end(&ssa->extern_funcs);
+    u32 extern_funcs_size = 0;
 
     for(; extern_func != extern_func_end; ++extern_func) {
         extern_funcs_size += sizeof(u8) + sizeof(u8) + extern_func->name.size + 1; /* +1 for null-termination of string */
@@ -158,9 +170,9 @@ static void add_extern_functions(BytecodeCompilerContext *self) {
     throw_if_error(buffer_append(instructions, &extern_funcs_size, sizeof(u32)));
     for(; extern_func != extern_func_end; ++extern_func) {
         const char null_s = '\0';
-        u8 num_args;
-        num_args = buffer_get_size(&extern_func->func_sig->parameters, FunctionParameter);
+        u8 num_args = buffer_get_size(&extern_func->func_sig->parameters, FunctionParameter);
         throw_if_error(buffer_append(instructions, &num_args, sizeof(num_args)));
+        /* TODO: Add namespace to the function name */
         throw_if_error(buffer_append(instructions, &extern_func->name.size, sizeof(u8)));
         throw_if_error(buffer_append(instructions, extern_func->name.data, extern_func->name.size));
         throw_if_error(buffer_append(instructions, &null_s, sizeof(char)));
@@ -169,6 +181,51 @@ static void add_extern_functions(BytecodeCompilerContext *self) {
     assert(sizeof(SsaExternFuncIndex) == sizeof(u16) && "Program decoder needs to be updated since size of extern func index has changed");
 }
 
+static void add_export_functions(BytecodeCompilerContext *self) {
+    /*doc(Bytecode exported functions)
+        # Exported functions layout
+        |Type             |Field             |Description                                                                              |
+        |-----------------|------------------|-----------------------------------------------------------------------------------------|
+        |u16              |num_export_func   |The number of exported functions.                                                        |
+        |u32              |export_funcs_size |The size of the exported functions section, in bytes.                                    |
+        |Exported function|Exported functions|Multiple exported functions, where the number of functions is defined by @num_export_func|
+
+        # Exported function
+        |Type|Field             |Description                                                                                                               |
+        |----|------------------|--------------------------------------------------------------------------------------------------------------------------|
+        |u32 |instruction_offset|The offset in the instruction data where the exported function is defined. Is always 0 until the program has been started.|
+        |u8  |num_args          |The number of arguments the functions has.                                                                                |
+        |u8  |name_len          |The length of the exported function name, in bytes. Excluding the null-terminate character.                               |
+        |u8* |name              |The name of the exported function, where the size is defined by @name_len. Names are null-terminated.                     |
+    */
+    Ssa *ssa = self->parser->ssa;
+    Buffer *instructions = &self->bytecode.data;
+    SsaExportFunc *export_func = buffer_begin(&ssa->export_funcs);
+    SsaExportFunc *export_func_end = buffer_end(&ssa->export_funcs);
+    u32 export_funcs_size = 0;
+
+    for(; export_func != export_func_end; ++export_func) {
+        export_funcs_size += sizeof(u32) + sizeof(u8) + sizeof(u8) + export_func->name.size + 1; /* +1 for null-termination of string */
+    }
+    export_func = buffer_begin(&ssa->export_funcs);
+
+    throw_if_error(buffer_expand(instructions, sizeof(u16) + sizeof(u32) + export_funcs_size));
+    throw_if_error(buffer_append(instructions, &ssa->export_func_counter, sizeof(u16)));
+    throw_if_error(buffer_append(instructions, &export_funcs_size, sizeof(u32)));
+    for(; export_func != export_func_end; ++export_func) {
+        const char null_s = '\0';
+        const u32 instruction_offset = 0;
+        u8 num_args = buffer_get_size(&export_func->func_sig->parameters, FunctionParameter);
+        throw_if_error(buffer_append(instructions, &instruction_offset, sizeof(instruction_offset)));
+        throw_if_error(buffer_append(instructions, &num_args, sizeof(num_args)));
+        throw_if_error(buffer_append(instructions, &export_func->name.size, sizeof(u8)));
+        throw_if_error(buffer_append(instructions, export_func->name.data, export_func->name.size));
+        throw_if_error(buffer_append(instructions, &null_s, sizeof(char)));
+    }
+
+    assert(sizeof(SsaExportFuncIndex) == sizeof(u16) && "Program decoder needs to be updated since size of export func index has changed");
+}
+
 static void add_ins1(BytecodeCompilerContext *self, AmalOpcode opcode, const char *fmt) {
     throw_if_error(buffer_append(&self->bytecode.data, &opcode, sizeof(AmalOpcodeType)));
     fprintf(stderr, fmt);
@@ -177,10 +234,8 @@ static void add_ins1(BytecodeCompilerContext *self, AmalOpcode opcode, const cha
 
 
 static void add_ins2(BytecodeCompilerContext *self, AmalOpcode opcode, i8 reg, const char *fmt) {
-    Buffer *instructions;
-    size_t index;
-    instructions = &self->bytecode.data;
-    index = instructions->size;
+    Buffer *instructions = &self->bytecode.data;
+    size_t index = instructions->size;
     
     throw_if_error(buffer_append_empty(instructions, sizeof(AmalOpcodeType) + sizeof(reg)));
     instructions->data[index] = opcode;
@@ -190,10 +245,8 @@ static void add_ins2(BytecodeCompilerContext *self, AmalOpcode opcode, i8 reg, c
 }
 
 static void add_ins3(BytecodeCompilerContext *self, AmalOpcode opcode, i8 dst_reg, i8 src_reg, const char *fmt) {
-    Buffer *instructions;
-    size_t index;
-    instructions = &self->bytecode.data;
-    index = instructions->size;
+    Buffer *instructions = &self->bytecode.data;
+    size_t index = instructions->size;
     
     throw_if_error(buffer_append_empty(instructions, sizeof(AmalOpcodeType) + sizeof(dst_reg) + sizeof(src_reg)));
     instructions->data[index] = opcode;
@@ -204,10 +257,8 @@ static void add_ins3(BytecodeCompilerContext *self, AmalOpcode opcode, i8 dst_re
 }
 
 static void add_ins4(BytecodeCompilerContext *self, AmalOpcode opcode, u16 data, const char *fmt) {
-    Buffer *instructions;
-    size_t index;
-    instructions = &self->bytecode.data;
-    index = instructions->size;
+    Buffer *instructions = &self->bytecode.data;
+    size_t index = instructions->size;
     
     throw_if_error(buffer_append_empty(instructions, sizeof(AmalOpcodeType) + sizeof(data)));
     instructions->data[index] = opcode;
@@ -217,10 +268,8 @@ static void add_ins4(BytecodeCompilerContext *self, AmalOpcode opcode, u16 data,
 }
 
 static void add_ins5(BytecodeCompilerContext *self, AmalOpcode opcode, i8 dst_reg, i8 reg1, i8 reg2, const char *fmt) {
-    Buffer *instructions;
-    size_t index;
-    instructions = &self->bytecode.data;
-    index = instructions->size;
+    Buffer *instructions = &self->bytecode.data;
+    size_t index = instructions->size;
     
     throw_if_error(buffer_append_empty(instructions, sizeof(AmalOpcodeType) + sizeof(dst_reg) + sizeof(reg1) + sizeof(reg2)));
     instructions->data[index] = opcode;
@@ -232,10 +281,8 @@ static void add_ins5(BytecodeCompilerContext *self, AmalOpcode opcode, i8 dst_re
 }
 
 static void add_ins6(BytecodeCompilerContext *self, AmalOpcode opcode, i8 dst_reg, u16 data, const char *fmt) {
-    Buffer *instructions;
-    size_t index;
-    instructions = &self->bytecode.data;
-    index = instructions->size;
+    Buffer *instructions = &self->bytecode.data;
+    size_t index = instructions->size;
     
     throw_if_error(buffer_append_empty(instructions, sizeof(AmalOpcodeType) + sizeof(dst_reg) + sizeof(data)));
     instructions->data[index] = opcode;
@@ -246,10 +293,8 @@ static void add_ins6(BytecodeCompilerContext *self, AmalOpcode opcode, i8 dst_re
 }
 
 static void add_ins7(BytecodeCompilerContext *self, AmalOpcode opcode, u16 idx, i8 num_args, i8 dst_reg, const char *fmt) {
-    Buffer *instructions;
-    size_t index;
-    instructions = &self->bytecode.data;
-    index = instructions->size;
+    Buffer *instructions = &self->bytecode.data;
+    size_t index = instructions->size;
     
     throw_if_error(buffer_append_empty(instructions, sizeof(AmalOpcodeType) + sizeof(idx) + sizeof(num_args) + sizeof(dst_reg)));
     instructions->data[index] = opcode;
@@ -260,25 +305,6 @@ static void add_ins7(BytecodeCompilerContext *self, AmalOpcode opcode, u16 idx,
     fputc('\n', stderr);
 }
 
-#if 0
-#define NUM_MAX_REGS 256
-#define NUM_MAX_FUNC_ARGS 32
-
-static const char* lhs_expr_get_c_name(BytecodeCompilerContext *self, LhsExpr *lhs_expr) {
-    if(lhs_expr == self->parser->compiler->default_types.i64) {
-        return "i64";
-    } else if(lhs_expr == self->parser->compiler->default_types.f64) {
-        return "f64";
-    } else if(lhs_expr == self->parser->compiler->default_types.str) {
-        return"const char*";
-    } else {
-        amal_log_error("Invalid rhs type %p", lhs_expr);
-        assert(bool_false && "TODO: Implement");
-        return "";
-    }
-}
-#endif
-
 static void add_instructions(BytecodeCompilerContext *self) {
     /*doc(Bytecode instructions)
         # Instructions layout
@@ -359,7 +385,7 @@ static void add_instructions(BytecodeCompilerContext *self) {
             }
             case SSA_FUNC_START: {
                 instruction += ssa_extract_data(instruction, &ssa_ins_func_start, sizeof(ssa_ins_func_start));
-                add_ins6(self, AMAL_OP_FUNC_START, ssa_ins_func_start.num_params_regs, ssa_ins_func_start.num_local_vars_regs, "func_start %d, %u");
+                add_ins6(self, AMAL_OP_FUNC_START, ssa_ins_func_start.flags, ssa_ins_func_start.num_local_vars_regs, "func_start 0x%02x, %u");
                 break;
             }
             case SSA_FUNC_END: {
@@ -424,5 +450,6 @@ void generate_bytecode_from_ssa(BytecodeCompilerContext *self) {
     add_strings(self);
     add_functions(self);
     add_extern_functions(self);
+    add_export_functions(self);
     add_instructions(self);
 }
diff --git a/src/compiler.c b/src/compiler.c
index fd9e4ae..3ccb86a 100644
--- a/src/compiler.c
+++ b/src/compiler.c
@@ -373,14 +373,17 @@ int amal_compiler_load_file(amal_compiler_options *options, amal_program *progra
     return result;
 }
 
-/* TODO: Verify main func has correct signature */
+/*
+    TODO: Instead of using amal_log_error, print error message with tokenizer to show where the error is.
+    This requires finding tokenizer by code reference.
+*/
 static CHECK_RESULT int validate_main_func(FileScopeReference *main_file_scope, LhsExpr **main_func) {
     const BufferView main_func_name = { "main", 4 };
     LhsExpr *main_func_expr;
 
     main_func_expr = structdecl_get_field_by_name(&main_file_scope->parser->struct_decl, main_func_name);
     if(!main_func_expr) {
-        amal_log_error("main function missing from start file \"%.*s\"", main_file_scope->canonical_path.size, main_file_scope->canonical_path.data);
+        amal_log_error("main function missing from start file \"%.*s\". Note: the main function has to be in the file scope.", main_file_scope->canonical_path.size, main_file_scope->canonical_path.data);
         return AMAL_COMPILER_ERR;
     }
     *main_func = main_func_expr;
@@ -400,6 +403,19 @@ static CHECK_RESULT int validate_main_func(FileScopeReference *main_file_scope,
         return AMAL_COMPILER_ERR;
     }
 
+    {
+        const FunctionDecl *func_decl = main_func_expr->rhs_expr->value.func_decl;
+        if(buffer_get_size(&func_decl->signature->parameters, FunctionParameter) != 0) {
+            amal_log_error("main function in start file \"%.*s\" has to be a closure with no parameters", main_file_scope->canonical_path.size, main_file_scope->canonical_path.data);
+            return AMAL_COMPILER_ERR;
+        }
+
+        if(buffer_get_size(&func_decl->signature->return_types, FunctionReturnType) != 0) {
+            amal_log_error("main function in start file \"%.*s\" has to be a closure that doesn't return anything", main_file_scope->canonical_path.size, main_file_scope->canonical_path.data);
+            return AMAL_COMPILER_ERR;
+        }
+    }
+
     return 0;
 }
 
@@ -437,6 +453,7 @@ int amal_compiler_internal_load_file(amal_compiler *self, const char *filepath,
         */
         LhsExpr *main_func;
 
+        /* Wait for all parsing to be done */
         if(!thread_pool_join_all_tasks(&self->stage_task_thread_pool))
             return -1;
         amal_log_info("Finished parsing all files, resolving AST");
diff --git a/src/parser.c b/src/parser.c
index 85165d7..ff34663 100644
--- a/src/parser.c
+++ b/src/parser.c
@@ -267,12 +267,13 @@ void parser_parse_var_type_def(Parser *self, VariableType *result) {
 }
 
 /*
-LHS_DECLARATION = 'extern'? 'pub'? 'const'|'var' TOK_IDENTIFIER VAR_TYPE_DEF?
+LHS_DECLARATION = ('extern'|'export')? 'pub'? 'const'|'var' TOK_IDENTIFIER VAR_TYPE_DEF?
 */
 static CHECK_RESULT LhsExpr* parser_parse_declaration_lhs(Parser *self) {
     LhsExpr *result;
     DeclFlag decl_flag;
     bool is_extern;
+    bool is_export;
     bool is_pub;
     bool is_const;
     BufferView var_name;
@@ -283,10 +284,21 @@ static CHECK_RESULT LhsExpr* parser_parse_declaration_lhs(Parser *self) {
         decl_flag |= DECL_FLAG_EXTERN;
         if(self->has_func_parent) {
             self->error = tokenizer_create_error(&self->tokenizer,
-                                                tokenizer_get_code_reference_index(&self->tokenizer, self->tokenizer.value.identifier.data),
+                                                tokenizer_get_error_index(&self->tokenizer),
                                                 "Only declarations in global structs can be extern");
             throw(PARSER_UNEXPECTED_TOKEN);
         }
+    } else {
+        throw_if_error(tokenizer_consume_if(&self->tokenizer, TOK_EXPORT, &is_export));
+        if(is_export) {
+            decl_flag |= DECL_FLAG_EXPORT;
+            if(self->has_func_parent) {
+                self->error = tokenizer_create_error(&self->tokenizer,
+                                                    tokenizer_get_error_index(&self->tokenizer),
+                                                    "Only declarations in global structs can be exported");
+                throw(PARSER_UNEXPECTED_TOKEN);
+            }
+        }
     }
 
     throw_if_error(tokenizer_consume_if(&self->tokenizer, TOK_PUB, &is_pub));
@@ -294,7 +306,7 @@ static CHECK_RESULT LhsExpr* parser_parse_declaration_lhs(Parser *self) {
         decl_flag |= DECL_FLAG_PUB;
         if(self->has_func_parent) {
             self->error = tokenizer_create_error(&self->tokenizer,
-                                                tokenizer_get_code_reference_index(&self->tokenizer, self->tokenizer.value.identifier.data),
+                                                tokenizer_get_error_index(&self->tokenizer),
                                                 "Only declarations in global structs can be public");
             throw(PARSER_UNEXPECTED_TOKEN);
         }
@@ -306,10 +318,10 @@ static CHECK_RESULT LhsExpr* parser_parse_declaration_lhs(Parser *self) {
     } else {
         bool isVar;
 
-        if(is_extern) {
+        if(is_extern || is_export) {
             self->error = tokenizer_create_error(&self->tokenizer,
-                                            tokenizer_get_code_reference_index(&self->tokenizer, self->tokenizer.value.identifier.data),
-                                            "Extern variable have to be declared with \"const\"");
+                                                tokenizer_get_error_index(&self->tokenizer),
+                                                "Extern and exported variables have to be declared with \"const\"");
             throw(PARSER_UNEXPECTED_TOKEN);
         }
 
@@ -732,10 +744,10 @@ static Ast* parser_parse_lhs_rhs(Parser *self, LhsExpr *lhs_expr) {
 
     func_decl = parser_parse_closure(self);
     if(func_decl) {
-        if(buffer_get_size(&func_decl->signature->return_types, FunctionReturnType) > 1 && LHS_EXPR_IS_EXTERN(lhs_expr)) {
+        if(buffer_get_size(&func_decl->signature->return_types, FunctionReturnType) > 1 && (LHS_EXPR_IS_EXTERN(lhs_expr) || LHS_EXPR_IS_EXPORT(lhs_expr))) {
             self->error = tokenizer_create_error(&self->tokenizer,
                                                  tokenizer_get_code_reference_index(&self->tokenizer, lhs_expr->var_name.data),
-                                                 "Extern closure can only have one return value");
+                                                 "Extern and export closures can only have one return value");
             throw(PARSER_ERR);
         }
         throw_if_error(ast_create(self->allocator, func_decl, AST_FUNCTION_DECL, &result));
@@ -796,7 +808,7 @@ Ast* parser_parse_body(Parser *self) {
         if(LHS_EXPR_IS_EXTERN(lhs_expr)) {
             throw_if_error(tokenizer_accept(&self->tokenizer, TOK_SEMICOLON));
             if (lhs_expr->type.type == VARIABLE_TYPE_NONE) {
-                self->error = tokenizer_create_error(&self->tokenizer, self->tokenizer.prev_index, "A variable can't be declared without a type or assignment");
+                self->error = tokenizer_create_error(&self->tokenizer, tokenizer_get_code_reference_index(&self->tokenizer, lhs_expr->var_name.data), "An extern variable can't be declared without a type");
                 throw(PARSER_UNEXPECTED_TOKEN);
             }
             return result;
@@ -804,10 +816,14 @@ Ast* parser_parse_body(Parser *self) {
             throw_if_error(tokenizer_consume_if(&self->tokenizer, TOK_SEMICOLON, &match));
             if(match) {
                 if(lhs_expr->type.type == VARIABLE_TYPE_SIGNATURE) {
-                    self->error = tokenizer_create_error(&self->tokenizer, self->tokenizer.prev_index, "Expected function declaration. Only extern functions can have empty declarations.");
+                    self->error = tokenizer_create_error(&self->tokenizer, tokenizer_get_code_reference_index(&self->tokenizer, lhs_expr->var_name.data), "Expected function declaration. Only extern functions can have empty declarations.");
                     throw(PARSER_UNEXPECTED_TOKEN);
                 } else if (lhs_expr->type.type == VARIABLE_TYPE_NONE) {
-                    self->error = tokenizer_create_error(&self->tokenizer, self->tokenizer.prev_index, "A variable can't be declared without a type or assignment");
+                    /* TODO: Allow this for non-const variables */
+                    self->error = tokenizer_create_error(&self->tokenizer, tokenizer_get_code_reference_index(&self->tokenizer, lhs_expr->var_name.data), "A variable can't be declared without a type or assignment");
+                    throw(PARSER_UNEXPECTED_TOKEN);
+                } else if(LHS_EXPR_IS_CONST(lhs_expr)) {
+                    self->error = tokenizer_create_error(&self->tokenizer, tokenizer_get_code_reference_index(&self->tokenizer, lhs_expr->var_name.data), "A const variable can't be declared without assignment");
                     throw(PARSER_UNEXPECTED_TOKEN);
                 }
                 return result;
diff --git a/src/program.c b/src/program.c
index 082f9fd..8a17ac9 100644
--- a/src/program.c
+++ b/src/program.c
@@ -26,52 +26,26 @@ typedef struct {
     NumberUnion value;
 } Number;
 
-/*doc(Bytecode)
-The layout of the full bytecode is: Header (Intermediates Strings Functions External_Functions Instructions)*
-*/
-
-static CHECK_RESULT int amal_program_append_header(amal_program *self) {
-    /*doc(Bytecode header)
-        # Header layout
-        |Type|Field        |Description                                                                 |
-        |----|-------------|----------------------------------------------------------------------------|
-        |u32 |Magic number |The magic number used to identify an amalgam bytecode file.                 |
-        |u8  |Major version|The major version of the bytecode. Updates in this is a breaking change.    |
-        |u8  |Minor version|The minor version of the bytecode. Updates in this are backwards compatible.|
-        |u8  |Patch version|The patch version of the bytecode. Updates in this are only minor bug fixes.|
-
-        The versions in the header only changes for every release, not every change.
-    */
-
-    const u32 magic_number = AMAL_PROGRAM_MAGIC_NUMBER;
-    const u8 major_version = AMAL_PROGRAM_MAJOR_VERSION;
-    const u8 minor_version = AMAL_PROGRAM_MINOR_VERSION;
-    const u8 patch_version = AMAL_PROGRAM_PATCH_VERSION;
-
-    return_if_error(buffer_append(&self->data, &magic_number, 4));
-    return_if_error(buffer_append(&self->data, &major_version, 1));
-    return_if_error(buffer_append(&self->data, &minor_version, 1));
-    return_if_error(buffer_append(&self->data, &patch_version, 1));
-
-    return 0;
-}
-
 int amal_program_init(amal_program *self) {
     ignore_result_int(buffer_init(&self->data, NULL));
-    self->string_indices = NULL;
-    self->extern_func_indices = NULL;
-    self->intermediates_start = NULL;
-    self->strings_start = NULL;
-    self->extern_funcs_start = NULL;
-    self->read_index = 0;
-    self->num_intermediates = 0;
-    self->num_strings = 0;
-    self->num_functions = 0;
-    self->num_extern_functions = 0;
+    self->string_indices                = NULL;
+    self->extern_func_indices           = NULL;
+    self->intermediates_start           = NULL;
+    self->strings_start                 = NULL;
+    self->extern_funcs_start            = NULL;
+    self->exported_funcs                = NULL;
+    self->exported_funcs_end            = NULL;
+    self->read_index                    = 0;
+    self->main_func_instruction_offset  = ~0U;
+    self->num_intermediates             = 0;
+    self->num_strings                   = 0;
+    self->num_functions                 = 0;
+    self->num_extern_functions          = 0;
+    self->num_exported_functions        = 0;
 
     cleanup_if_error(arena_allocator_init(&self->allocator));
     cleanup_if_error(hash_map_init(&self->extern_funcs_map, &self->allocator, sizeof(ProgramExternFunc), hash_map_compare_string, amal_hash_string));
-    cleanup_if_error(amal_program_append_header(self));
+    cleanup_if_error(buffer_append_header(&self->data));
     return 0;
 
     cleanup:
@@ -131,6 +105,36 @@ static CHECK_RESULT int amal_program_get_extern_func_by_index(amal_program *self
     return 0;
 }
 
+static CHECK_RESULT int amal_program_set_exported_function_instruction_offset_advance(amal_program *self, u32 instruction_offset) {
+    if(self->exported_funcs >= self->exported_funcs_end) {
+        amal_log_error("The number of exported functions in the instructions is more than the number of exported instructions in the header");
+        return AMAL_PROGRAM_INSTRUCTION_INVALID_EXPORTED_FUNC_INDEX;
+    }
+
+    {
+        u8 num_args;
+        u8 func_name_size;
+
+        if((usize)(self->exported_funcs_end - self->exported_funcs) < sizeof(instruction_offset) + sizeof(num_args) + sizeof(func_name_size))
+            return AMAL_PROGRAM_INSTRUCTION_INVALID_EXPORTED_FUNC_INDEX;
+
+        am_memcpy(self->exported_funcs, &instruction_offset, sizeof(instruction_offset));
+        num_args = self->exported_funcs[sizeof(instruction_offset)];
+        func_name_size = self->exported_funcs[sizeof(instruction_offset) + sizeof(num_args)];
+        self->exported_funcs += sizeof(instruction_offset) + sizeof(num_args) + sizeof(func_name_size);
+        if(self->main_func_instruction_offset == ~0U && am_memeql(self->exported_funcs, "main", 4))
+            self->main_func_instruction_offset = instruction_offset;
+
+        /* +1 to skip null-termination character */
+        if((usize)(self->exported_funcs_end - self->exported_funcs) < func_name_size + 1U)
+            return AMAL_PROGRAM_INSTRUCTION_INVALID_EXPORTED_FUNC_INDEX;
+
+        self->exported_funcs += func_name_size + 1; /* +1 to skip null-termination character */
+    }
+
+    return 0;
+}
+
 int amal_program_append_bytecode(amal_program *self, Bytecode *bytecode) {
     return buffer_append(&self->data, bytecode->data.data, bytecode->data.size);
 }
@@ -158,14 +162,14 @@ static CHECK_RESULT int amal_program_read_header(amal_program *self) {
     am_memcpy(&patch_version, &self->data.data[self->read_index], sizeof(patch_version));
     self->read_index += sizeof(u8);
 
-    if(magic_number != AMAL_PROGRAM_MAGIC_NUMBER)
+    if(magic_number != AMAL_BYTECODE_MAGIC_NUMBER)
         return AMAL_PROGRAM_INVALID_MAGIC_NUMBER;
 
     /*
         A program is only incompatible if the major version is newer than the version that is used to run it.
         TODO: Implement backwards compatible reads, starting from when the program bytecode breaks backwards compatibility
     */
-    if(major_version > AMAL_PROGRAM_MAJOR_VERSION)
+    if(major_version > AMAL_BYTECODE_MAJOR_VERSION)
         return AMAL_PROGRAM_INCOMPATIBLE;
 
     return AMAL_PROGRAM_OK;
@@ -237,7 +241,7 @@ static CHECK_RESULT int amal_program_read_strings(amal_program *self) {
             am_memcpy(&string_size, &self->data.data[self->read_index], sizeof(string_size));
             self->read_index += sizeof(string_size);
 
-             /* +1 to skip null-termination character */
+            /* +1 to skip null-termination character */
             if(bytes_left_to_read(self) < string_size + 1U)
                 return AMAL_PROGRAM_INVALID_STRINGS;
 
@@ -291,9 +295,9 @@ static CHECK_RESULT int amal_program_read_external_functions(amal_program *self)
             func_name_size = self->data.data[self->read_index + sizeof(num_args)];
             self->read_index += sizeof(num_args) + sizeof(func_name_size);
 
-             /* +1 to skip null-termination character */
+            /* +1 to skip null-termination character */
             if(bytes_left_to_read(self) < func_name_size + 1U)
-                return AMAL_PROGRAM_INVALID_STRINGS;
+                return AMAL_PROGRAM_INVALID_EXTERNAL_FUNCTIONS;
 
             self->read_index += func_name_size + 1; /* +1 to skip null-termination character */
         }
@@ -303,6 +307,28 @@ static CHECK_RESULT int amal_program_read_external_functions(amal_program *self)
     return AMAL_PROGRAM_OK;
 }
 
+static CHECK_RESULT int amal_program_read_exported_functions(amal_program *self) {
+    u32 export_funcs_size;
+
+    if(!amal_program_read_advance(self, &self->num_exported_functions, sizeof(u16)))
+        return AMAL_PROGRAM_INVALID_EXPORTED_FUNCTIONS;
+
+    if(!amal_program_read_advance(self, &export_funcs_size, sizeof(export_funcs_size)))
+        return AMAL_PROGRAM_INVALID_EXPORTED_FUNCTIONS;
+
+    if(bytes_left_to_read(self) < export_funcs_size)
+        return AMAL_PROGRAM_INVALID_EXPORTED_FUNCTIONS_SIZE;
+
+    /*
+        Exported functions doesn't need list of indices to the data, since exported functions
+        are always sorted in the instructions in the same order as list of exported functions
+    */
+    self->exported_funcs = (u8*)(self->data.data + self->read_index);
+    self->exported_funcs_end = self->exported_funcs + export_funcs_size;
+    self->read_index += export_funcs_size;
+    return AMAL_PROGRAM_OK;
+}
+
 static CHECK_RESULT int amal_program_get_intermediate_by_index(amal_program *self, u16 index, Number *result) {
     if(index >= self->num_intermediates)
         return AMAL_PROGRAM_INSTRUCTION_INVALID_INTERMEDIATE_INDEX;
@@ -507,7 +533,7 @@ static CHECK_RESULT int amal_program_read_instructions(amal_program *self, amal_
                 break;
             }
             case AMAL_OP_FUNC_START: {
-                u8 func_num_param_regs;
+                u8 func_flags;
                 u16 func_num_local_var_regs;
 
                 assert(!inside_func);
@@ -515,9 +541,10 @@ static CHECK_RESULT int amal_program_read_instructions(amal_program *self, amal_
                 assert(func_counter < self->num_functions);
                 ++func_counter;
 
-                func_num_param_regs = self->data.data[self->read_index];
-                (void)func_num_param_regs;
-                am_memcpy(&func_num_local_var_regs, self->data.data + self->read_index + sizeof(func_num_param_regs), sizeof(func_num_local_var_regs));
+                func_flags = self->data.data[self->read_index];
+                am_memcpy(&func_num_local_var_regs, self->data.data + self->read_index + sizeof(func_flags), sizeof(func_num_local_var_regs));
+                if(func_flags & FUNC_FLAG_EXPORTED)
+                    return_if_error(amal_program_set_exported_function_instruction_offset_advance(self, amal_exec_get_code_offset(executor)));
                 return_if_error(amal_exec_func_start(executor, func_num_local_var_regs));
                 self->read_index += 3;
                 break;
@@ -549,9 +576,15 @@ int amal_program_run(amal_program *self) {
         cleanup_if_error(amal_program_read_strings(self));
         cleanup_if_error(amal_program_read_functions(self));
         cleanup_if_error(amal_program_read_external_functions(self));
+        cleanup_if_error(amal_program_read_exported_functions(self));
         cleanup_if_error(amal_program_read_instructions(self, executor));
     }
-    result = amal_executor_run(executor);
+    if(self->main_func_instruction_offset == ~0U) {
+        amal_log_error("The program is missing a main function");
+        result = AMAL_PROGRAM_NO_MAIN_FUNC;
+        goto cleanup;
+    }
+    result = amal_executor_run(executor, self->main_func_instruction_offset);
 
     cleanup:
     amal_executor_deinit(executor);
diff --git a/src/ssa/ssa.c b/src/ssa/ssa.c
index 500555a..940f636 100644
--- a/src/ssa/ssa.c
+++ b/src/ssa/ssa.c
@@ -61,9 +61,11 @@ int ssa_init(Ssa *self, Parser *parser) {
     return_if_error(buffer_init(&self->strings, parser->allocator));
     return_if_error(hash_map_init(&self->extern_funcs_map, parser->allocator, sizeof(SsaExternFuncIndex), hash_map_compare_string, amal_hash_string));
     return_if_error(buffer_init(&self->extern_funcs, parser->allocator));
+    return_if_error(buffer_init(&self->export_funcs, parser->allocator));
     self->intermediate_counter = 0;
     self->string_counter = 0;
     self->extern_func_counter = 0;
+    self->export_func_counter = 0;
     self->reg_counter = 0;
     self->param_counter = 0;
     self->func_counter = 0;
@@ -192,6 +194,29 @@ static CHECK_RESULT int ssa_try_add_extern_func(Ssa *self, FunctionSignature *fu
     }
 }
 
+/*
+    Exported functions with the same name are allowed to exist in different files, but not in the same file.
+    There is no need to check if there are two exported functions with the same name in the same file
+    as that is already checked in the AST stage, as you are not allowed to have multiple variables of the same name in the same scope,
+    exported or not.
+*/
+static CHECK_RESULT int ssa_try_add_export_func(Ssa *self, FunctionSignature *func_sig, BufferView name) {
+    /* Overflow */
+    if(self->export_func_counter + 1 <= self->export_func_counter) {
+        amal_log_error("Ssa too many exported closures!");
+        return -1;
+    }
+    
+    amal_log_debug("ef%u = \"%.*s\"", self->export_func_counter, name.size, name.data);
+    ++self->export_func_counter;
+    {
+        SsaExportFunc export_func;
+        export_func.func_sig = func_sig;
+        export_func.name = name;
+        return buffer_append(&self->export_funcs, &export_func, sizeof(export_func));
+    }
+}
+
 static CHECK_RESULT int ssa_add_ins_form1(Ssa *self, SsaInstruction ins_type, SsaRegister lhs, u16 rhs) {
     SsaInsForm1 ins_form_1;
     ins_form_1.lhs = lhs;
@@ -247,7 +272,7 @@ static CHECK_RESULT int ssa_ins_binop(Ssa *self, SsaInstruction binop_type, SsaR
     return ssa_add_ins_form2(self, binop_type, lhs, rhs, result);
 }
 
-static CHECK_RESULT int ssa_ins_func_start(Ssa *self, SsaRegister num_reg_params, SsaFuncIndex *result, usize *func_metadata_index) {
+static CHECK_RESULT int ssa_ins_func_start(Ssa *self, u8 func_flags, SsaFuncIndex *result, usize *func_metadata_index) {
     const u8 ins_type = SSA_FUNC_START;
     SsaInsFuncStart ins_func_start;
 
@@ -258,14 +283,13 @@ static CHECK_RESULT int ssa_ins_func_start(Ssa *self, SsaRegister num_reg_params
     }
 
     *result = self->func_counter++;
-    ins_func_start.func_index = *result;
-    ins_func_start.num_params_regs = num_reg_params;
+    ins_func_start.flags = func_flags;
     /* Dont set number of local registers yet. That will be set by @func_metadata_index later when it's known */
     /*ins_func_start.num_local_vars_regs = ---*/
     return_if_error(buffer_append(&self->instructions, &ins_type, 1));
     return_if_error(buffer_append(&self->instructions, &ins_func_start, sizeof(ins_func_start)));
     *func_metadata_index = self->instructions.size - sizeof(ins_func_start.num_local_vars_regs);
-    amal_log_debug("FUNC_START f%u, %d", *result, num_reg_params);
+    amal_log_debug("FUNC_START f%u", *result);
     return 0;
 }
 
@@ -428,6 +452,16 @@ static CHECK_RESULT SsaRegister lhsexpr_extern_generate_ssa(LhsExpr *self, SsaCo
     return 0;
 }
 
+static CHECK_RESULT SsaRegister lhsexpr_export_generate_ssa(LhsExpr *self, SsaCompilerContext *context) {
+    /* TODO: SsaRegister should be extended to include static and export data */
+    if(self->rhs_expr->type == AST_FUNCTION_DECL) {
+        throw_if_error(ssa_try_add_export_func(context->ssa, self->rhs_expr->value.func_decl->signature, self->var_name));
+    } else {
+        assert(bool_false && "TODO: Implement lhsexpr_export_generate_ssa for other data than functions");
+    }
+    return 0;
+}
+
 static CHECK_RESULT SsaRegister lhsexpr_generate_ssa(LhsExpr *self, AstResolveData *resolve_data, SsaCompilerContext *context) {
     SsaRegister reg;
 
@@ -438,6 +472,10 @@ static CHECK_RESULT SsaRegister lhsexpr_generate_ssa(LhsExpr *self, AstResolveDa
         Ast *rhs_expr = self->rhs_expr;
         SsaRegister rhs_reg;
         rhs_reg = ast_generate_ssa(rhs_expr, context);
+
+        if(LHS_EXPR_IS_EXPORT(self))
+            return lhsexpr_export_generate_ssa(self, context);
+
         /*
             Declarations (struct and function declaration) resolves to itself and in that case this expression
             is just a compile-time name for the declaration.
@@ -513,15 +551,13 @@ in any order.
 static CHECK_RESULT SsaRegister funcdecl_generate_ssa(FunctionDecl *self, SsaCompilerContext *context) {
     /* TODO: Implement */
     /*
-    Reset reg counter in each function, because each function has a separate register context
-    that is reset after function end
+        Reset reg counter in each function, because each function has a separate register context
+        that is reset after function end
     */
-    SsaRegister prev_reg_counter;
-    SsaRegister prev_param_counter;
     usize func_metadata_index;
-
-    prev_reg_counter = context->ssa->reg_counter;
-    prev_param_counter = context->ssa->param_counter;
+    SsaRegister prev_reg_counter = context->ssa->reg_counter;
+    SsaRegister prev_param_counter = context->ssa->param_counter;
+    u8 func_flags = 0;
     context->ssa->reg_counter = 0;
 
     /* 
@@ -533,7 +569,12 @@ static CHECK_RESULT SsaRegister funcdecl_generate_ssa(FunctionDecl *self, SsaCom
     context->ssa->reg_counter = 0;
 
     amal_log_debug("SSA funcdecl %p", self);
-    throw_if_error(ssa_ins_func_start(context->ssa, context->ssa->param_counter, &self->ssa_func_index, &func_metadata_index));
+    /* Anonymous closure doesn't have lhs_expr, and neither can it have any flags (extern, export etc) */
+    if(self->lhs_expr) {
+        if(LHS_EXPR_IS_EXPORT(self->lhs_expr))
+            func_flags |= FUNC_FLAG_EXPORTED;
+    }
+    throw_if_error(ssa_ins_func_start(context->ssa, func_flags, &self->ssa_func_index, &func_metadata_index));
     scope_generate_ssa(&self->body, context);
     throw_if_error(ssa_ins_func_end(context->ssa));
 
@@ -585,7 +626,7 @@ static CHECK_RESULT SsaRegister structdecl_generate_ssa(StructDecl *self, SsaCom
 
 static CHECK_RESULT SsaRegister structfield_generate_ssa(StructField *self, SsaCompilerContext *context) {
     /* TODO: Implement */
-    /*assert(bool_false);*/
+    assert(bool_false);
     (void)self;
     (void)context;
     return 0;
@@ -644,8 +685,7 @@ static CHECK_RESULT SsaRegister binop_generate_ssa(Binop *self, SsaCompilerConte
 }
 
 static void else_if_statement_generate_ssa(ElseIfStatement *else_if_stmt, SsaCompilerContext *context) {
-    usize jump_ins_index;
-    jump_ins_index = 0;
+    usize jump_ins_index = 0;
     if(else_if_stmt->condition) {
         SsaRegister condition_reg;
         condition_reg = ast_generate_ssa(else_if_stmt->condition, context);
@@ -660,11 +700,8 @@ static void else_if_statement_generate_ssa(ElseIfStatement *else_if_stmt, SsaCom
 }
 
 static void if_statement_generate_ssa(IfStatement *if_stmt, SsaCompilerContext *context) {
-    SsaRegister condition_reg;
-    usize jump_ins_index;
-
-    condition_reg = ast_generate_ssa(if_stmt->condition, context);
-    jump_ins_index = ssa_ins_get_index(context->ssa);
+    SsaRegister condition_reg = ast_generate_ssa(if_stmt->condition, context);
+    usize jump_ins_index = ssa_ins_get_index(context->ssa);
     throw_if_error(ssa_ins_jumpzero(context->ssa, condition_reg, 0));
     scope_generate_ssa(&if_stmt->body, context);
     throw_if_error(ssa_ins_jump_set_target(context->ssa, jump_ins_index));
@@ -673,14 +710,10 @@ static void if_statement_generate_ssa(IfStatement *if_stmt, SsaCompilerContext *
 }
 
 static void while_statement_generate_ssa(WhileStatement *while_stmt, SsaCompilerContext *context) {
-    SsaRegister condition_reg;
-    usize jump_back_ins_index;
-    usize jump_condition_ins_index;
     isize jump_offset;
-
-    jump_back_ins_index = ssa_ins_get_index(context->ssa);
-    condition_reg = ast_generate_ssa(while_stmt->condition, context);
-    jump_condition_ins_index = ssa_ins_get_index(context->ssa);
+    usize jump_back_ins_index = ssa_ins_get_index(context->ssa);
+    SsaRegister condition_reg = ast_generate_ssa(while_stmt->condition, context);
+    usize jump_condition_ins_index = ssa_ins_get_index(context->ssa);
     throw_if_error(ssa_ins_jumpzero(context->ssa, condition_reg, 0));
     scope_generate_ssa(&while_stmt->body, context);
     /* Jump back and check condition again before running the content of the loop again */
diff --git a/src/tokenizer.c b/src/tokenizer.c
index 556a20b..82ea0f6 100644
--- a/src/tokenizer.c
+++ b/src/tokenizer.c
@@ -217,6 +217,9 @@ static CHECK_RESULT int __tokenizer_next(Tokenizer *self, Token *token) {
                 } else if(am_memeql(self->value.identifier.data, "extern", 6)) {
                     *token = TOK_EXTERN;
                     return TOKENIZER_OK;
+                } else if(am_memeql(self->value.identifier.data, "export", 6)) {
+                    *token = TOK_EXPORT;
+                    return TOKENIZER_OK;
                 } else if(am_memeql(self->value.identifier.data, "return", 6)) {
                     *token = TOK_RETURN;
                     return TOKENIZER_OK;
@@ -496,6 +499,9 @@ static BufferView tokenizer_expected_token_as_string(Token token) {
         case TOK_EXTERN:
             str = "extern";
             break;
+        case TOK_EXPORT:
+            str = "export";
+            break;
         case TOK_RETURN:
             str = "return";
             break;
diff --git a/tests/bytecode.amal b/tests/bytecode.amal
index a8ea53b..32c1ccb 100644
--- a/tests/bytecode.amal
+++ b/tests/bytecode.amal
@@ -1,8 +1,10 @@
-const b = @import("b.amal");
-
 extern const print_extern: fn;
 extern const print_extern_num: fn(num: i32);
 
+const print = fn {
+
+}
+
 const main = fn {
     var value = 23;
     value = 34;
@@ -15,10 +17,6 @@ const main = fn {
     const result = print_num(1337);
 }
 
-const print = fn {
-
-}
-
 const print_num = fn(num: i32) i32 {
     print_extern();
     print_extern_num(num);
diff --git a/tests/errors/incorrect_main.amal b/tests/errors/incorrect_main.amal
new file mode 100644
index 0000000..9d2a61f
--- /dev/null
+++ b/tests/errors/incorrect_main.amal
@@ -0,0 +1 @@
+const main = fn(arg: i32) {}
\ No newline at end of file
diff --git a/tests/main.c b/tests/main.c
index 3573f9c..b2b53cc 100644
--- a/tests/main.c
+++ b/tests/main.c
@@ -279,6 +279,7 @@ static void run_all_tests() {
     test_load_error("tests/errors/closure_duplicate_param_name.amal", "TODO: Add expected error here");
     test_load_error("tests/errors/extern_closure_one_return_value.amal", "TODO: Add expected error here");
     test_load_error("tests/errors/too_long_var_name.amal", "TODO: Add expected error here");
+    test_load_error("tests/errors/incorrect_main.amal", "TODO: Add expected error here");
 }
 
 /* TODO: Restrict variables in global scope to const */