FunC Cookbook
The core reason for creating the FunC Cookbook is to collect all the experience from FunC developers in one place so that future developers will use it!
Compared to the FunC Documentation, this article is more focused on the everyday tasks of every FunC developer to resolve during the development of smart contracts.
Basics
How to write an if statement
Let's say we want to check if any event is relevant. To do this, we use the flag variable. Remember that in FunC true is -1 and false is 0.
int flag = 0; ;; false
if (flag) {
;; do something
}
else {
;; reject the transaction
}
💡 Noted
We do not need the operator
==, because the value0isfalse, so any other value will betrue.
💡 Useful links
How to write a repeat loop
As an example, we can take exponentiation
int number = 2;
int multiplier = number;
int degree = 5;
repeat(degree - 1) {
number *= multiplier;
}
💡 Useful links
How to write a while loop
While is useful when we do not know how often to perform a particular action. For example, take a cell, which is known to store up to four references to other cells.
cell inner_cell = begin_cell() ;; create a new empty builder
.store_uint(123, 16) ;; store uint with value 123 and length 16 bits
.end_cell(); ;; convert builder to a cell
cell message = begin_cell()
.store_ref(inner_cell) ;; store cell as reference
.store_ref(inner_cell)
.end_cell();
slice msg = message.begin_parse(); ;; convert cell to slice
while (msg.slice_refs_empty?() != -1) { ;; we should remind that -1 is true
cell inner_cell = msg~load_ref(); ;; load cell from slice msg
;; do something
}
💡 Useful links
How to write a do until loop
When we need the cycle to run at least once, we use do until.
int flag = 0;
do {
;; do something even flag is false (0)
} until (flag == -1); ;; -1 is true
💡 Useful links
How to determine if slice is empty
Before working with slice, it is necessary to check whether it has any data to process it correctly. We can use slice_empty?() to do this, but we have to consider that it will return 0 (false) if there is at least one bit of data or one ref.
;; creating empty slice
slice empty_slice = "";
;; `slice_empty?()` returns `true`, because slice doesn't have any `bits` and `refs`
empty_slice.slice_empty?();
;; creating slice which contains bits only
slice slice_with_bits_only = "Hello, world!";
;; `slice_empty?()` returns `false`, because slice have any `bits`
slice_with_bits_only.slice_empty?();
;; creating slice which contains refs only
slice slice_with_refs_only = begin_cell()
.store_ref(null())
.end_cell()
.begin_parse();
;; `slice_empty?()` returns `false`, because slice have any `refs`
slice_with_refs_only.slice_empty?();
;; creating slice which contains bits and refs
slice slice_with_bits_and_refs = begin_cell()
.store_slice("Hello, world!")
.store_ref(null())
.end_cell()
.begin_parse();
;; `slice_empty?()` returns `false`, because slice have any `bits` and `refs`
slice_with_bits_and_refs.slice_empty?();
💡 Useful links
How to determine if slice is empty (doesn't have any bits, but may have refs)
If we need to check only the bits and it does not matter if there are any refs in slice, then we should use slice_data_empty?().
;; creating empty slice
slice empty_slice = "";
;; `slice_data_empty?()` returns `true`, because slice doesn't have any `bits`
empty_slice.slice_data_empty?();
;; creating slice which contains bits only
slice slice_with_bits_only = "Hello, world!";
;; `slice_data_empty?()` returns `false`, because slice have any `bits`
slice_with_bits_only.slice_data_empty?();
;; creating slice which contains refs only
slice slice_with_refs_only = begin_cell()
.store_ref(null())
.end_cell()
.begin_parse();
;; `slice_data_empty?()` returns `true`, because slice doesn't have any `bits`
slice_with_refs_only.slice_data_empty?();
;; creating slice which contains bits and refs
slice slice_with_bits_and_refs = begin_cell()
.store_slice("Hello, world!")
.store_ref(null())
.end_cell()
.begin_parse();
;; `slice_data_empty?()` returns `false`, because slice have any `bits`
slice_with_bits_and_refs.slice_data_empty?();
💡 Useful links
How to determine if slice is empty (doesn't have any refs, but may have bits)
In case we are only interested in refs, we should check their presence using slice_refs_empty?().
;; creating empty slice
slice empty_slice = "";
;; `slice_refs_empty?()` returns `true`, because slice doesn't have any `refs`
empty_slice.slice_refs_empty?();
;; creating slice which contains bits only
slice slice_with_bits_only = "Hello, world!";
;; `slice_refs_empty?()` returns `true`, because slice doesn't have any `refs`
slice_with_bits_only.slice_refs_empty?();
;; creating slice which contains refs only
slice slice_with_refs_only = begin_cell()
.store_ref(null())
.end_cell()
.begin_parse();
;; `slice_refs_empty?()` returns `false`, because slice have any `refs`
slice_with_refs_only.slice_refs_empty?();
;; creating slice which contains bits and refs
slice slice_with_bits_and_refs = begin_cell()
.store_slice("Hello, world!")
.store_ref(null())
.end_cell()
.begin_parse();
;; `slice_refs_empty?()` returns `false`, because slice have any `refs`
slice_with_bits_and_refs.slice_refs_empty?();
💡 Useful links
How to determine if cell is empty
To check if there is any data in a cell, we should first convert it to slice. If we are only interested in having bits, we should use slice_data_empty?(), if only refs - slice_refs_empty?(). In case we want to check the presence of any data regardless of whether it is a bit or ref, we need to use slice_empty?().
cell cell_with_bits_and_refs = begin_cell()
.store_uint(1337, 16)
.store_ref(null())
.end_cell();
;; Change `cell` type to slice with `begin_parse()`
slice cs = cell_with_bits_and_refs.begin_parse();
;; determine if slice is empty
if (cs.slice_empty?()) {
;; cell is empty
}
else {
;; cell is not empty
}
💡 Useful links
How to determine if dict is empty
There is a method of dict_empty?() to check the data presence in dict. This method is the equivalent of cell_null?() because usually a null-cell is an empty dictionary.
cell d = new_dict();
d~udict_set(256, 0, "hello");
d~udict_set(256, 1, "world");
if (d.dict_empty?()) { ;; Determine if dict is empty
;; dict is empty
}
else {
;; dict is not empty
}
💡 Useful links
"new_dict()" in docs creating an empty dict
"dict_set()" in docs adding some elements in dict d with function, so it is not empty
How to determine if tuple is empty
When working with tuples, it is important always to know if any values are inside for extraction. If we try to extract value from an empty tuple, we get an error: "not a tuple of valid size" with exit code 7.
;; Declare tlen function because it's not presented in stdlib
(int) tlen (tuple t) asm "TLEN";
() main () {
tuple t = empty_tuple();
t~tpush(13);
t~tpush(37);
if (t.tlen() == 0) {
;; tuple is empty
}
else {
;; tuple is not empty
}
}
💡 Noted
We are declaring tlen assembly function. You can read more here and see list of all assembler commands.
💡 Useful links
How to determine if lisp-style list is empty
tuple numbers = null();
numbers = cons(100, numbers);
if (numbers.null?()) {
;; list-style list is empty
} else {
;; list-style list is not empty
}
We are adding number 100 to our list-style list with cons function, so it's not empty.
How to determine a state of the contract is empty
Let’s say we have a counter that stores the number of transactions. This variable is not available during the first transaction in the smart contract state, because the state is empty, so it is necessary to process such a case. If the state is empty, we create a variable counter and save it.
;; `get_data()` will return the data cell from contract state
cell contract_data = get_data();
slice cs = contract_data.begin_parse();
if (cs.slice_empty?()) {
;; contract data is empty, so we create counter and save it
int counter = 1;
;; create cell, add counter and save in contract state
set_data(begin_cell().store_uint(counter, 32).end_cell());
}
else {
;; contract data is not empty, so we get our counter, increase it and save
;; we should specify correct length of our counter in bits
int counter = cs~load_uint(32) + 1;
set_data(begin_cell().store_uint(counter, 32).end_cell());
}
💡 Noted
We can determine that state of contract is empty by determining that cell is empty.
💡 Useful links
How to build an internal message cell
If we want the contract to send an internal message, we should first properly create it as a cell, specifying the technical flags, the recipient address, and the rest data.
;; We use literal `a` to get valid address inside slice from string containing address
slice addr = "EQArzP5prfRJtDM5WrMNWyr9yUTAi0c9o6PfR4hkWy9UQXHx"a;
int amount = 1000000000;
;; we use `op` for identifying operations
int op = 0;
cell msg = begin_cell()
.store_uint(0x18, 6)
.store_slice(addr)
.store_coins(amount)
.store_uint(0, 1 + 4 + 4 + 64 + 32 + 1 + 1) ;; default message headers (see sending messages page)
.store_uint(op, 32)
.end_cell();
send_raw_message(msg, 3); ;; mode 3 - pay fees separately and ignore errors
💡 Noted
In this example, we use literal
ato get address. You can find more about string literals in docs
💡 Noted
You can find more in docs. Also, you can jump in layout with this link.
💡 Useful links
How to contain a body as ref to an internal message cell
In the body of a message that follows flags and other technical data, we can send int, slice, and cell. In the case of the latter, it is necessary to set the bit to 1 before store_ref() to indicate that the cell will go on.
We can also send the body of the message inside the same cell as header, if we are sure that we have enough space. In this case, we need to set the bit to 0.
;; We use literal `a` to get valid address inside slice from string containing address
slice addr = "EQArzP5prfRJtDM5WrMNWyr9yUTAi0c9o6PfR4hkWy9UQXHx"a;
int amount = 1000000000;
int op = 0;
cell message_body = begin_cell() ;; Creating a cell with message
.store_uint(op, 32)
.store_slice("❤")
.end_cell();
cell msg = begin_cell()
.store_uint(0x18, 6)
.store_slice(addr)
.store_coins(amount)
.store_uint(0, 1 + 4 + 4 + 64 + 32 + 1) ;; default message headers (see sending messages page)
.store_uint(1, 1) ;; set bit to 1 to indicate that the cell will go on
.store_ref(message_body)
.end_cell();
send_raw_message(msg, 3); ;; mode 3 - pay fees separately and ignore errors
💡 Noted
In this example, we use literal
ato get address. You can find more about string literals in docs
💡 Noted
In this example, we used mode 3 to take the incoming tons and send exactly as much as specified (amount) while paying commission from the contract balance and ignoring the errors. Mode 64 is needed to return all the tons received, subtracting the commission, and mode 128 will send the entire balance.
💡 Noted
We are building a message but adding message body separetly.
💡 Useful links
How to contain a body as slice to an internal message cell
When sending messages, the body message can be sent either as cell or as slice. In this example, we send the body of the message inside the slice.
;; We use literal `a` to get valid address inside slice from string containing address
slice addr = "EQArzP5prfRJtDM5WrMNWyr9yUTAi0c9o6PfR4hkWy9UQXHx"a;
int amount = 1000000000;
int op = 0;
slice message_body = "❤";
cell msg = begin_cell()
.store_uint(0x18, 6)
.store_slice(addr)
.store_coins(amount)
.store_uint(0, 1 + 4 + 4 + 64 + 32 + 1 + 1) ;; default message headers (see sending messages page)
.store_uint(op, 32)
.store_slice(message_body)
.end_cell();
send_raw_message(msg, 3); ;; mode 3 - pay fees separately and ignore errors
💡 Noted
In this example, we use literal
ato get address. You can find more about string literals in docs
💡 Noted
In this example, we used mode 3 to take the incoming tons and send exactly as much as specified (amount) while paying commission from the contract balance and ignoring the errors. Mode 64 is needed to return all the tons received, subtracting the commission, and mode 128 will send the entire balance.
💡 Noted
We are building a message but adding message as a slice.
How to iterate tuples (in both directions)
If we want to work with an array or stack in FunC, then tuple will be necessary there. And first of all we need to be able to iterate values to work with them.
(int) tlen (tuple t) asm "TLEN";
forall X -> (tuple) to_tuple (X x) asm "NOP";
() main () {
tuple t = to_tuple([1, 2, 3, 4, 5, 6, 7, 8, 9, 10]);
int len = t.tlen();
int i = 0;
while (i < len) {
int x = t.at(i);
;; do something with x
i = i + 1;
}
i = len - 1;
while (i >= 0) {
int x = t.at(i);
;; do something with x
i = i - 1;
}
}
💡 Noted
We are declaring
tlenassembly function. You can read more here and see list of all assembler commands.Also we declaring
to_tuplefunction. It just changes data type of any input to tuple, so be careful while using it.
How to write own functions using asm keyword
When using any features we actually use pre-prepared for us methods inside stdlib.fc. But in fact, we have many more opportunities available to us, and we need to learn to write them ourselves.
For example, we have the method of tpush, which adds an element to tuple, but without tpop. In this case, we should do this:
;; ~ means it is modifying method
forall X -> (tuple, X) ~tpop (tuple t) asm "TPOP";
If we want to know the length of tuple for iteration, we should write a new function with the TLEN asm instruction:
int tuple_length (tuple t) asm "TLEN";
Some examples of functions already known to us from stdlib.fc:
slice begin_parse(cell c) asm "CTOS";
builder begin_cell() asm "NEWC";
cell end_cell(builder b) asm "ENDC";
💡 Useful links:
Iterating n-nested tuples
Sometimes we want to iterate nested tuples. The following example will iterate and print all of the items in a tuple of format [[2,6],[1,[3,[3,5]]], 3] starting from the head
int tuple_length (tuple t) asm "TLEN";
forall X -> (tuple, X) ~tpop (tuple t) asm "TPOP";
forall X -> int is_tuple (X x) asm "ISTUPLE";
forall X -> tuple cast_to_tuple (X x) asm "NOP";
forall X -> int cast_to_int (X x) asm "NOP";
forall X -> (tuple) to_tuple (X x) asm "NOP";
;; define global variable
global int max_value;
() iterate_tuple (tuple t) impure {
repeat (t.tuple_length()) {
var value = t~tpop();
if (is_tuple(value)) {
tuple tuple_value = cast_to_tuple(value);
iterate_tuple(tuple_value);
}
else {
if(value > max_value) {
max_value = value;
}
}
}
}
() main () {
tuple t = to_tuple([[2,6], [1, [3, [3, 5]]], 3]);
int len = t.tuple_length();
max_value = 0; ;; reset max_value;
iterate_tuple(t); ;; iterate tuple and find max value
~dump(max_value); ;; 6
}
💡 Useful links
Basic operations with tuples
(int) tlen (tuple t) asm "TLEN";
forall X -> (tuple, X) ~tpop (tuple t) asm "TPOP";
() main () {
;; creating an empty tuple
tuple names = empty_tuple();
;; push new items
names~tpush("Naito Narihira");
names~tpush("Shiraki Shinichi");
names~tpush("Akamatsu Hachemon");
names~tpush("Takaki Yuichi");
;; pop last item
slice last_name = names~tpop();
;; get first item
slice first_name = names.first();
;; get an item by index
slice best_name = names.at(2);
;; getting the length of the list
int number_names = names.tlen();
}
Resolving type X
The following example checks if some value is contained in a tuple, but tuple contains values X (cell, slice, int, tuple, int). We need to check the value and cast accordingly.
forall X -> int is_null (X x) asm "ISNULL";
forall X -> int is_int (X x) asm "<{ TRY:<{ 0 PUSHINT ADD DROP -1 PUSHINT }>CATCH<{ 2DROP 0 PUSHINT }> }>CONT 1 1 CALLXARGS";
forall X -> int is_cell (X x) asm "<{ TRY:<{ CTOS DROP -1 PUSHINT }>CATCH<{ 2DROP 0 PUSHINT }> }>CONT 1 1 CALLXARGS";
forall X -> int is_slice (X x) asm "<{ TRY:<{ SBITS DROP -1 PUSHINT }>CATCH<{ 2DROP 0 PUSHINT }> }>CONT 1 1 CALLXARGS";
forall X -> int is_tuple (X x) asm "ISTUPLE";
forall X -> int cast_to_int (X x) asm "NOP";
forall X -> cell cast_to_cell (X x) asm "NOP";
forall X -> slice cast_to_slice (X x) asm "NOP";
forall X -> tuple cast_to_tuple (X x) asm "NOP";
forall X -> (tuple, X) ~tpop (tuple t) asm "TPOP";
forall X -> () resolve_type (X value) impure {
;; value here is of type X, since we dont know what is the exact value - we would need to check what is the value and then cast it
if (is_null(value)) {
;; do something with the null
}
elseif (is_int(value)) {
int valueAsInt = cast_to_int(value);
;; do something with the int
}
elseif (is_slice(value)) {
slice valueAsSlice = cast_to_slice(value);
;; do something with the slice
}
elseif (is_cell(value)) {
cell valueAsCell = cast_to_cell(value);
;; do something with the cell
}
elseif (is_tuple(value)) {
tuple valueAsTuple = cast_to_tuple(value);
;; do something with the tuple
}
}
() main () {
;; creating an empty tuple
tuple stack = empty_tuple();
;; let's say we have tuple and do not know the exact types of them
stack~tpush("Some text");
stack~tpush(4);
;; we use var because we do not know type of value
var value = stack~tpop();
resolve_type(value);
}
💡 Useful links
How to get current time
int current_time = now();
if (current_time > 1672080143) {
;; do some stuff
}
How to generate random number
Please note that this method of generating random numbers isn't safe.
Checkout Random Number Generation for more information.
randomize_lt(); ;; do this once
int a = rand(10);
int b = rand(1000000);
int c = random();
Modulo operations
As an example, lets say that we want to run the following calculation of all 256 numbers : (xp + zp)*(xp-zp). Since most of those operations are used for cryptography, in the following example we are using the modulo operator for montogomery curves.
Note that xp+zp is a valid variable name ( without spaces between ).
(int) modulo_operations (int xp, int zp) {
;; 2^255 - 19 is a prime number for montgomery curves, meaning all operations should be done against its prime
int prime = 57896044618658097711785492504343953926634992332820282019728792003956564819949;
;; muldivmod handles the next two lines itself
;; int xp+zp = (xp + zp) % prime;
;; int xp-zp = (xp - zp + prime) % prime;
(_, int xp+zp*xp-zp) = muldivmod(xp + zp, xp - zp, prime);
return xp+zp*xp-zp;
}
💡 Useful links
How to throw errors
int number = 198;
throw_if(35, number > 50); ;; the error will be triggered only if the number is greater than 50
throw_unless(39, number == 198); ;; the error will be triggered only if the number is NOT EQUAL to 198
throw(36); ;; the error will be triggered anyway
Reversing tuples
Because tuple stores data as a stack, sometimes we have to reverse tuple to read data from the other end.
forall X -> (tuple, X) ~tpop (tuple t) asm "TPOP";
int tuple_length (tuple t) asm "TLEN";
forall X -> (tuple) to_tuple (X x) asm "NOP";
(tuple) reverse_tuple (tuple t1) {
tuple t2 = empty_tuple();
repeat (t1.tuple_length()) {
var value = t1~tpop();
t2~tpush(value);
}
return t2;
}
() main () {
tuple t = to_tuple([1, 2, 3, 4, 5, 6, 7, 8, 9, 10]);
tuple reversed_t = reverse_tuple(t);
~dump(reversed_t); ;; [10 9 8 7 6 5 4 3 2 1]
}
💡 Useful links
How to remove an item with a certain index from the list
int tlen (tuple t) asm "TLEN";
(tuple, ()) remove_item (tuple old_tuple, int place) {
tuple new_tuple = empty_tuple();
int i = 0;
while (i < old_tuple.tlen()) {
int el = old_tuple.at(i);
if (i != place) {
new_tuple~tpush(el);
}
i += 1;
}
return (new_tuple, ());
}
() main () {
tuple numbers = empty_tuple();
numbers~tpush(19);
numbers~tpush(999);
numbers~tpush(54);
~dump(numbers); ;; [19 999 54]
numbers~remove_item(1);
~dump(numbers); ;; [19 54]
}
Determine if slices are equal
There are two different ways we can determine the equality. One is based on the slice hash, while the other one by using the SDEQ asm instruction.
int are_slices_equal_1? (slice a, slice b) {
return a.slice_hash() == b.slice_hash();
}
int are_slices_equal_2? (slice a, slice b) asm "SDEQ";
() main () {
slice a = "Some text";
slice b = "Some text";
~dump(are_slices_equal_1?(a, b)); ;; -1 = true
a = "Text";
;; We use literal `a` to get valid address inside slice from string containing address
b = "EQDKbjIcfM6ezt8KjKJJLshZJJSqX7XOA4ff-W72r5gqPrHF"a;
~dump(are_slices_equal_2?(a, b)); ;; 0 = false
}
💡 Useful links
Determine if cells are equal
We can easily determine cell equality based on their hash.
int are_cells_equal? (cell a, cell b) {
return a.cell_hash() == b.cell_hash();
}
() main () {
cell a = begin_cell()
.store_uint(123, 16)
.end_cell();
cell b = begin_cell()
.store_uint(123, 16)
.end_cell();
~dump(are_cells_equal?(a, b)); ;; -1 = true
}
💡 Useful links
Determine if tuples are equal
A more advanced example would be to iterate and compare each of the tuple values. Since they are X we need to check and cast to the corresponding type and if it is tuple to iterate it recursively.
int tuple_length (tuple t) asm "TLEN";
forall X -> (tuple, X) ~tpop (tuple t) asm "TPOP";
forall X -> int cast_to_int (X x) asm "NOP";
forall X -> cell cast_to_cell (X x) asm "NOP";
forall X -> slice cast_to_slice (X x) asm "NOP";
forall X -> tuple cast_to_tuple (X x) asm "NOP";
forall X -> int is_null (X x) asm "ISNULL";
forall X -> int is_int (X x) asm "<{ TRY:<{ 0 PUSHINT ADD DROP -1 PUSHINT }>CATCH<{ 2DROP 0 PUSHINT }> }>CONT 1 1 CALLXARGS";
forall X -> int is_cell (X x) asm "<{ TRY:<{ CTOS DROP -1 PUSHINT }>CATCH<{ 2DROP 0 PUSHINT }> }>CONT 1 1 CALLXARGS";
forall X -> int is_slice (X x) asm "<{ TRY:<{ SBITS DROP -1 PUSHINT }>CATCH<{ 2DROP 0 PUSHINT }> }>CONT 1 1 CALLXARGS";
forall X -> int is_tuple (X x) asm "ISTUPLE";
int are_slices_equal? (slice a, slice b) asm "SDEQ";
int are_cells_equal? (cell a, cell b) {
return a.cell_hash() == b.cell_hash();
}
(int) are_tuples_equal? (tuple t1, tuple t2) {
int equal? = -1; ;; initial value to true
if (t1.tuple_length() != t2.tuple_length()) {
;; if tuples are differ in length they cannot be equal
return 0;
}
int i = t1.tuple_length();
while (i > 0 & equal?) {
var v1 = t1~tpop();
var v2 = t2~tpop();
if (is_null(t1) & is_null(t2)) {
;; nulls are always equal
}
elseif (is_int(v1) & is_int(v2)) {
if (cast_to_int(v1) != cast_to_int(v2)) {
equal? = 0;
}
}
elseif (is_slice(v1) & is_slice(v2)) {
if (~ are_slices_equal?(cast_to_slice(v1), cast_to_slice(v2))) {
equal? = 0;
}
}
elseif (is_cell(v1) & is_cell(v2)) {
if (~ are_cells_equal?(cast_to_cell(v1), cast_to_cell(v2))) {
equal? = 0;
}
}
elseif (is_tuple(v1) & is_tuple(v2)) {
;; recursively determine nested tuples
if (~ are_tuples_equal?(cast_to_tuple(v1), cast_to_tuple(v2))) {
equal? = 0;
}
}
else {
equal? = 0;
}
i -= 1;
}
return equal?;
}
() main () {
tuple t1 = cast_to_tuple([[2, 6], [1, [3, [3, 5]]], 3]);
tuple t2 = cast_to_tuple([[2, 6], [1, [3, [3, 5]]], 3]);
~dump(are_tuples_equal?(t1, t2)); ;; -1
}
💡 Useful links
Generate internal address
We need to generate an internal address when our contract should deploy a new contract, but do not know his address. Suppose we already have state_init - the code and data of the new contract.
Creates an internal address for the corresponding MsgAddressInt TLB.
(slice) generate_internal_address (int workchain_id, cell state_init) {
;; addr_std$10 anycast:(Maybe Anycast) workchain_id:int8 address:bits256 = MsgAddressInt;
return begin_cell()
.store_uint(2, 2) ;; addr_std$10
.store_uint(0, 1) ;; anycast nothing
.store_int(workchain_id, 8) ;; workchain_id: -1
.store_uint(cell_hash(state_init), 256)
.end_cell().begin_parse();
}
() main () {
slice deploy_address = generate_internal_address(workchain(), state_init);
;; then we can deploy new contract
}
💡 Noted
In this example, we use
workchain()to get id of workchain. You can find more about Workchain ID in docs.
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Generate external address
We use the TL-B scheme from block.tlb to understand how we need to create an address in this format.
(int) ubitsize (int a) asm "UBITSIZE";
slice generate_external_address (int address) {
;; addr_extern$01 len:(## 9) external_address:(bits len) = MsgAddressExt;
int address_length = ubitsize(address);
return begin_cell()
.store_uint(1, 2) ;; addr_extern$01
.store_uint(address_length, 9)
.store_uint(address, address_length)
.end_cell().begin_parse();
}
Since we need to determine the number of bits occupied by the address, it is also necessary to declare an asm function with the opcode UBITSIZE, which will return the minimum number of bits required to store the number.
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How to store and load dictionary in local storage
The logic for loading the dictionary
slice local_storage = get_data().begin_parse();
cell dictionary_cell = new_dict();
if (~ slice_empty?(local_storage)) {
dictionary_cell = local_storage~load_dict();
}
While the logic for storing the dictionary is like the following example:
set_data(begin_cell().store_dict(dictionary_cell).end_cell());
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How to send a simple message
The usual way for us to send tons with a comment is actually a simple message. To specify that the body of the message is a comment, we should set 32 bits before the message text to 0.
cell msg = begin_cell()
.store_uint(0x18, 6) ;; flags
.store_slice("EQBIhPuWmjT7fP-VomuTWseE8JNWv2q7QYfsVQ1IZwnMk8wL"a) ;; destination address
.store_coins(100) ;; amount of nanoTons to send
.store_uint(0, 1 + 4 + 4 + 64 + 32 + 1 + 1) ;; default message headers (see sending messages page)
.store_uint(0, 32) ;; zero opcode - means simple transfer message with comment
.store_slice("Hello from FunC!") ;; comment
.end_cell();
send_raw_message(msg, 3); ;; mode 3 - pay fees separately, ignore errors
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How to send a message with an incoming account
The contract example below is useful to us if we need to perform any actions between the user and the main contract, that is, we need a proxy contract.
() recv_internal (slice in_msg_body) {
{-
This is a simple example of a proxy-contract.
It will expect in_msg_body to contain message mode, body and destination address to be sent to.
-}
int mode = in_msg_body~load_uint(8); ;; first byte will contain msg mode
slice addr = in_msg_body~load_msg_addr(); ;; then we parse the destination address
slice body = in_msg_body; ;; everything that is left in in_msg_body will be our new message's body
cell msg = begin_cell()
.store_uint(0x18, 6)
.store_slice(addr)
.store_coins(100) ;; just for example
.store_uint(0, 1 + 4 + 4 + 64 + 32 + 1 + 1) ;; default message headers (see sending messages page)
.store_slice(body)
.end_cell();
send_raw_message(msg, mode);
}
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How to send a message with the entire balance
If we need to send the entire balance of the smart contract, then, in this case, we need to use send mode 128. An example of such a case would be a proxy contract that accepts payments and forwards to the main contract.
cell msg = begin_cell()
.store_uint(0x18, 6) ;; flags
.store_slice("EQBIhPuWmjT7fP-VomuTWseE8JNWv2q7QYfsVQ1IZwnMk8wL"a) ;; destination address
.store_coins(0) ;; we don't care about this value right now
.store_uint(0, 1 + 4 + 4 + 64 + 32 + 1 + 1) ;; default message headers (see sending messages page)
.store_uint(0, 32) ;; zero opcode - means simple transfer message with comment
.store_slice("Hello from FunC!") ;; comment
.end_cell();
send_raw_message(msg, 128); ;; mode = 128 is used for messages that are to carry all the remaining balance of the current smart contract
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How to send a message with a long text comment
As we know, only 127 characters can fit into a single cell (< 1023 bits). In case we need more - we need to organize a snake cells.
{-
If we want to send a message with really long comment, we should split the comment to several slices.
Each slice should have <1023 bits of data (127 chars).
Each slice should have a reference to the next one, forming a snake-like structure.
-}
cell body = begin_cell()
.store_uint(0, 32) ;; zero opcode - simple message with comment
.store_slice("long long long message...")
.store_ref(begin_cell()
.store_slice(" you can store string of almost any length here.")
.store_ref(begin_cell()
.store_slice(" just don't forget about the 127 chars limit for each slice")
.end_cell())
.end_cell())
.end_cell();
cell msg = begin_cell()
.store_uint(0x18, 6) ;; flags
;; We use literal `a` to get valid address inside slice from string containing address
.store_slice("EQBIhPuWmjT7fP-VomuTWseE8JNWv2q7QYfsVQ1IZwnMk8wL"a) ;; destination address
.store_coins(100) ;; amount of nanoTons to send
.store_uint(0, 1 + 4 + 4 + 64 + 32 + 1) ;; default message headers (see sending messages page)
.store_uint(1, 1) ;; we want to store body as a ref
.store_ref(body)
.end_cell();
send_raw_message(msg, 3); ;; mode 3 - pay fees separately, ignore errors
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How to get only data bits from a slice (without refs)
If we are not interested in refs inside the slice, then we can get a separate date and work with it.
slice s = begin_cell()
.store_slice("Some data bits...")
.store_ref(begin_cell().end_cell()) ;; some references
.store_ref(begin_cell().end_cell()) ;; some references
.end_cell().begin_parse();
slice s_only_data = s.preload_bits(s.slice_bits());
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How to define your own modifying method
Modifying methods allow data to be modified within the same variable. This can be compared to referencing in other programming languages.
(slice, (int)) load_digit (slice s) {
int x = s~load_uint(8); ;; load 8 bits (one char) from slice
x -= 48; ;; char '0' has code of 48, so we substract it to get the digit as a number
return (s, (x)); ;; return our modified slice and loaded digit
}
() main () {
slice s = "258";
int c1 = s~load_digit();
int c2 = s~load_digit();
int c3 = s~load_digit();
;; here s is equal to "", and c1 = 2, c2 = 5, c3 = 8
}
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How to raise number to the power of n
;; Unoptimized variant
int pow (int a, int n) {
int i = 0;
int value = a;
while (i < n - 1) {
a *= value;
i += 1;
}
return a;
}
;; Optimized variant
(int) binpow (int n, int e) {
if (e == 0) {
return 1;
}
if (e == 1) {
return n;
}
int p = binpow(n, e / 2);
p *= p;
if ((e % 2) == 1) {
p *= n;
}
return p;
}
() main () {
int num = binpow(2, 3);
~dump(num); ;; 8
}
How to convert string to int
slice string_number = "26052021";
int number = 0;
while (~ string_number.slice_empty?()) {
int char = string_number~load_uint(8);
number = (number * 10) + (char - 48); ;; we use ASCII table
}
~dump(number);
How to convert int to string
int n = 261119911;
builder string = begin_cell();
tuple chars = null();
do {
int r = n~divmod(10);
chars = cons(r + 48, chars);
} until (n == 0);
do {
int char = chars~list_next();
string~store_uint(char, 8);
} until (null?(chars));
slice result = string.end_cell().begin_parse();
~dump(result);
How to iterate dictionaries
Dictionaries are very useful when working with a lot of data. We can get minimum and maximum key values using the built-in methods dict_get_min? and dict_get_max? respectively. Additionally, we can use dict_get_next? to iterate the dictionary.
cell d = new_dict();
d~udict_set(256, 1, "value 1");
d~udict_set(256, 5, "value 2");
d~udict_set(256, 12, "value 3");
;; iterate keys from small to big
(int key, slice val, int flag) = d.udict_get_min?(256);
while (flag) {
;; do something with pair key->val
(key, val, flag) = d.udict_get_next?(256, key);
}
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How to delete value from dictionaries
cell names = new_dict();
names~udict_set(256, 27, "Alice");
names~udict_set(256, 25, "Bob");
names~udict_delete?(256, 27);
(slice val, int key) = names.udict_get?(256, 27);
~dump(val); ;; null() -> means that key was not found in a dictionary
How to iterate cell tree recursively
As we know, one cell can store up to 1023 bits of data and up to 4 refs. To get around this limit, we can use a tree of cells, but to do this we need to be able to iterate it for proper data processing.
forall X -> int is_null (X x) asm "ISNULL";
forall X -> (tuple, ()) push_back (tuple tail, X head) asm "CONS";
forall X -> (tuple, (X)) pop_back (tuple t) asm "UNCONS";
() main () {
;; just some cell for example
cell c = begin_cell()
.store_uint(1, 16)
.store_ref(begin_cell()
.store_uint(2, 16)
.end_cell())
.store_ref(begin_cell()
.store_uint(3, 16)
.store_ref(begin_cell()
.store_uint(4, 16)
.end_cell())
.store_ref(begin_cell()
.store_uint(5, 16)
.end_cell())
.end_cell())
.end_cell();
;; creating tuple with no data, which plays the role of stack
tuple stack = null();
;; bring the main cell into the stack to process it in the loop
stack~push_back(c);
;; do it until stack is not null
while (~ stack.is_null()) {
;; get the cell from the stack and convert it to a slice to be able to process it
slice s = stack~pop_back().begin_parse();
;; do something with s data
;; if the current slice has any refs, add them to stack
repeat (s.slice_refs()) {
stack~push_back(s~load_ref());
}
}
}
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How to iterate through lisp-style list
The data type tuple can hold up to 255 values. If this is not enough, then we should use a lisp-style list. We can put a tuple inside a tuple, thus bypassing the limit.
forall X -> int is_null (X x) asm "ISNULL";
forall X -> (tuple, ()) push_back (tuple tail, X head) asm "CONS";
forall X -> (tuple, (X)) pop_back (tuple t) asm "UNCONS";
() main () {
;; some example list
tuple l = null();
l~push_back(1);
l~push_back(2);
l~push_back(3);
;; iterating through elements
;; note that this iteration is in reversed order
while (~ l.is_null()) {
var x = l~pop_back();
;; do something with x
}
}
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How to send a deploy message (with stateInit only, with stateInit and body)
() deploy_with_stateinit(cell message_header, cell state_init) impure {
var msg = begin_cell()
.store_slice(begin_parse(msg_header))
.store_uint(2 + 1, 2) ;; init:(Maybe (Either StateInit ^StateInit))
.store_uint(0, 1) ;; body:(Either X ^X)
.store_ref(state_init)
.end_cell();
;; mode 64 - carry the remaining value in the new message
send_raw_message(msg, 64);
}
() deploy_with_stateinit_body(cell message_header, cell state_init, cell body) impure {
var msg = begin_cell()
.store_slice(begin_parse(msg_header))
.store_uint(2 + 1, 2) ;; init:(Maybe (Either StateInit ^StateInit))
.store_uint(1, 1) ;; body:(Either X ^X)
.store_ref(state_init)
.store_ref(body)
.end_cell();
;; mode 64 - carry the remaining value in the new message
send_raw_message(msg, 64);
}
How to build a stateInit cell
() build_stateinit(cell init_code, cell init_data) {
var state_init = begin_cell()
.store_uint(0, 1) ;; split_depth:(Maybe (## 5))
.store_uint(0, 1) ;; special:(Maybe TickTock)
.store_uint(1, 1) ;; (Maybe ^Cell)
.store_uint(1, 1) ;; (Maybe ^Cell)
.store_uint(0, 1) ;; (HashmapE 256 SimpleLib)
.store_ref(init_code)
.store_ref(init_data)
.end_cell();
}
How to calculate a contract address (using stateInit)
() calc_address(cell state_init) {
var future_address = begin_cell()
.store_uint(2, 2) ;; addr_std$10
.store_uint(0, 1) ;; anycast:(Maybe Anycast)
.store_uint(0, 8) ;; workchain_id:int8
.store_uint(cell_hash(state_init), 256) ;; address:bits256
.end_cell();
}
How to update the smart contract logic
Below is a simple СounterV1 smart-contract that has the functionality to increment the counter and update the smart-contract logic.
() recv_internal (slice in_msg_body) {
int op = in_msg_body~load_uint(32);
if (op == op::increase) {
int increase_by = in_msg_body~load_uint(32);
ctx_counter += increase_by;
save_data();
return ();
}
if (op == op::upgrade) {
cell code = in_msg_body~load_ref();
set_code(code);
return ();
}
}
After operating the smart-contract, you realize that you are missing the meter reduction feature. You must copy the code of the smart-contract CounterV1 and next to the increase function, add a new decrease function. Now your code looks like this:
() recv_internal (slice in_msg_body) {
int op = in_msg_body~load_uint(32);
if (op == op::increase) {
int increase_by = in_msg_body~load_uint(32);
ctx_counter += increase_by;
save_data();
return ();
}
if (op == op::decrease) {
int decrease_by = in_msg_body~load_uint(32);
ctx_counter -= increase_by;
save_data();
return ();
}
if (op == op::upgrade) {
cell code = in_msg_body~load_ref();
set_code(code);
return ();
}
}
Once the smart-contract CounterV2 is ready, you must compile it off-chain into a cell and send an upgrade message to the CounterV1 smart-contract.
await contractV1.sendUpgrade(provider.sender(), {
code: await compile('ContractV2'),
value: toNano('0.05'),
});
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