06 — ERC-20 Token

The token keyword auto-synthesizes the entire ERC-20 surface from a metadata declaration. You write the name, symbol, decimals, and supply — the compiler generates every field, action, view, and event the standard requires.

-- Coin.cov · a standard ERC-20-conformant token.
-- The `token` keyword generates:
--   - fields: supply, balances, allowances, name, symbol, decimals
--   - actions: transfer, approve, transfer_from
--   - views:   balance_of, allowance
--   - events:  Transfer, Approval
-- The developer writes only the metadata and any custom logic.

token Coin {
    symbol: "COIN"
    name: "Covenant Coin"
    decimals: 18
    supply: 1_000_000 to deployer
}

What just happened?

Concept	Explanation
`token`	A specialized top-level keyword for ERC-20 fungible tokens
`symbol`, `name`, `decimals`	Plaintext metadata. `symbol`/`name` are `text`; `decimals` is `amount`
`supply: 1_000_000 to deployer`	Genesis mint declaration. The integer literal supports `_` thousand separators. `to deployer` says the entire supply is minted to the contract creator at deploy time
(no body needed)	Everything else is auto-synthesized: `balances` map, `allowances` map, `transfer`/`approve`/`transfer_from` actions, `Transfer`/`Approval` events. The ABI is byte-compatible with OpenZeppelin’s ERC-20

What gets generated, in detail

The compiler synthesizes the following surface (you can see it all in the playground’s Inspector → ABI tab):

Fields: total_supply: amount, balances: map<address, amount>, allowances: map<hash, amount>
Actions: transfer(to, value), approve(spender, value), transfer_from(from, to, value)
Views: balance_of(who) returns amount, allowance(owner, spender) returns amount, total_supply returns amount, decimals returns amount, symbol returns text, name returns text
Events: Transfer(from indexed, to indexed, value), Approval(owner indexed, spender indexed, value)

Add custom logic

You can add your own actions and views inside the token block. They compose with the auto-synthesized ones:

token MintableCoin {
    symbol: "MCOIN"
    name: "Mintable Coin"
    decimals: 18
    supply: 0 to deployer

    action mint(to: address, value: amount) only deployer {
        balances[to] += value
        total_supply += value
        emit Transfer(zero_address, to, value)
    }
}

The only deployer guard restricts mint to the contract creator. See 04 — Guards for the full guard catalog.

Try it now

Try in Playground →

In the playground:

Compile — note in the Inspector → ABI tab that you get all 7+ generated functions
Deploy to MockChain
Call balance_of(deployer) — returns 1000000000000000000000000 (1M with 18 decimals)
Call transfer(<your wallet>, 100_000000000000000000) — sends 100 tokens
Call balance_of on the recipient to verify

ERC-20 vs Confidential Token

Curious about a privacy-preserving variant? See 08 — Encrypted Token — same metadata-only declaration, but balances are TFHE ciphertexts (ERC-8227).

Continue

Move on to 07 — FHE Basics to learn how Covenant treats homomorphic encryption as a first-class language feature.