Smart contracts you can read.

The language in one page.

The full reference, including operators, error messages, and a security checklist, is in TCCL.md ↗ and the cookbook.

Contract layout

# Contract layout: constants, state, events and functions.
contract PiggyBank

const MINIMUM: int = 1 * TCN
state owner: address
state label: text = "Piggy bank"
state deposits: map[address, int]
state amounts: list[int]

event Deposited(who: address, amount: int)

init():
    owner = caller

action deposit() payable:
    require value >= MINIMUM, "minimum deposit is 1 TCN"
    deposits[caller] += value
    amounts.push(value)
    emit Deposited(caller, value)

action withdraw(amount: int):
    require amount > 0 and deposits[caller] >= amount, "insufficient balance"
    deposits[caller] -= amount
    send(caller, amount)

view balance_of(who: address) -> int:
    return deposits[who]

view total_held() -> int:
    return balance

fn half(x: int) -> int:
    return x / 2

Types

Default values are never stored: assigning 0, false, "", empty bytes or list, or the zero address deletes the storage entry. 5tcn is accepted only in command-line arguments — in source code write 5 * TCN.

Statements, context, and built-in functions

# Control flow, lists, maps and built-in functions.
contract Examples

state seen: map[bytes, bool]
state heights: list[int]

view sum_even(n: int) -> int:
    let total: int = 0
    for i in range(0, n):
        if i % 2 == 0:
            total += i
        elif i > 1000:
            break
        else:
            continue
    return total

view largest(xs: list[int]) -> int:
    require len(xs) > 0, "empty list"
    let m: int = xs[0]
    for x in xs:
        m = max(m, x)
    return m

view digest(t: text) -> bytes:
    return slice(sha256(t), 0, 4) + blake3(to_bytes(len(t)))

view label(n: int) -> text:
    return "value: " + to_text(abs(n))

view signature_ok(key: bytes, msg: bytes, sig: bytes) -> bool:
    return verify_ed25519(key, msg, sig)

view address_for_key(key: bytes) -> address:
    return address_of(key)

action mark(key: bytes):
    require not seen.has(key), "already marked"
    seen[key] = true
    heights.push(height)

action unmark(key: bytes):
    seen.remove(key)
    let n: int = 0
    while n < 3 and len(heights) > 0:
        heights.pop()
        n += 1

Closing a contract

# destroy(): deletes the contract and returns its balance and storage deposit.
contract Temporary

state owner: address
state notes: map[int, text]

init():
    owner = caller

action write(n: int, note: text):
    require caller == owner, "only the owner"
    notes[n] = note

action erase(n: int):
    require caller == owner, "only the owner"
    notes.remove(n)

action close():
    require caller == owner, "only the owner"
    destroy(owner)

destroy only works after every map entry and list item has been removed (scalar variables are cleared automatically). The balance and the whole storage deposit go to the given address.

Bounded, and priced by work.

Fuel prices are calibrated to roughly 20 ns of CPU per unit on a 2-vCPU server, so a completely full block executes in about a second in the worst case.

No surprises in the price.

The exact formulas (each division rounds up):

Worked example: the counter on mainnet

Mainnet defaults: base_fee 1,000 motes, fee_per_kb 10,000 motes, fee_per_kfuel 1,000 motes, and a storage_deposit_per_kb of 100,000 motes (1 TCN = 100,000,000 motes). Sizes and fuel come from the deployment above; no congestion (1×). The wallet’s normal priority pays 25% over the minimum.

After the first call the counter uses 367 bytes — still within 1 kB, so no extra deposit is locked. When blocks fill up, the congestion multiplier raises the minimum fee (at 2×, the deployment costs at least 31,152 motes) and the surcharge is burned rather than paid to the miner. These parameters can change through governance; see the live values in Explorer → Current fees.

Private payments with contract pools.

thecoin-wallet privacy keygen --key 0
thecoin-wallet privacy deposit tc1…pool --key 0
thecoin-wallet privacy status tc1…pool --key 0
thecoin-wallet privacy withdraw tc1…pool --key 0 \
    --to tc1…new --ring-size 16

Keep building.

Ready-made examples

Every example compiles with tccl check and is exercised by the test suite (cargo test -p tccl).