Arkade Functions

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Arkade Script is experimental. Do not fund contracts from it with real funds.

These are the built-in functions of Arkade Script. Most work only in covenants, the functions that compile to Arkade opcodes. A tapscript function can use only require with one optional hash check, one optional older or after, and one checkSig or checkMultisig. The compiler README has the full rules for each function.

require(checkSig(userSig, user), "invalid signature");
require(tx.outputs[0].value >= tx.input.current.value, "underpaid");

require(condition, "message") fails the spend if the condition is false. Every spend path needs at least one require.

Signatures

Function	Returns
`checkSig(sig, key)`	`bool`: `sig` is a valid signature by `key` for this spend
`checkMultisig(keys, sigs, threshold?)`	`bool`: at least `threshold` signatures are valid. Without a threshold, all must be valid
`checkSigFromStack(sig, key, message)`	`bool`: `sig` is a valid signature by `key` over `message`
`checkSigFromStackVerify(sig, key, message)`	Nothing. Use it directly inside `require`

A path that the operator accepts must be N-of-N, so a checkMultisig threshold in a tapscript function must equal the number of keys.

Hashes

Function	Returns
`sha256(data)`, `hash256(data)`	`bytes32`
`hash160(data)`, `ripemd160(data)`, `sha1(data)`	`bytes20`. `sha1` is broken; use it only for legacy formats
`sha256Initialize`, `sha256Update`, `sha256Finalize`	A SHA-256 hash computed in parts
`digest(data, hashType)`	A hash with a type chosen at spend time
`sighash(hashType)`	The digest that `checkSig` checks for this spend
`merkleRoot(leafTag, branchTag, proof, leaf)`	The `bytes32` root of a Merkle proof with BIP-341 tagged hashes

Time

Function	Use
`checkTime(timestamp)`	`bool`: the emulator’s clock has reached `timestamp` (Unix seconds). Covenants only
`this.expiry`	The expiry time of the virtual output being spent. Covenants only
`older(n)`	A relative delay (CSV). `tapscript` only. Use `older(serverExitDelay)` for exit paths
`after(n)`	An absolute time (CLTV). `tapscript` only
`seconds(n)`, `blocks(n)`	States the unit of an `older` or `after` value

tx.locktime is the transaction’s nLockTime, not a clock. Use checkTime for time conditions in covenants.

Transaction

Expression	Value
`tx.version`, `tx.locktime`, `tx.numInputs`, `tx.numOutputs`, `tx.weight`, `tx.id`	Fields of the spending transaction
`tx.inputs[i].value`, `.scriptPubKey`, `.sequence`, `.outpoint`	Fields of input `i`
`tx.outputs[o].value`, `.scriptPubKey`	Fields of output `o`
`tx.input.current`	The input being spent, with the same fields
`tx.packet(type)`	The raw bytes of an extension packet

scriptPubKey is the witness program, for example the 32-byte key of a Taproot output, not the full script.

Assets

Expression	Value
`tx.outputs[o].assets.lookup(txid, gidx)`	The amount of an asset in output `o`. Fails if the asset is absent
`.assets.has(txid, gidx)`	`bool`: the input or output holds the asset
`tx.assetGroups.find(txid, gidx)`	The asset group of the transaction, with `sumInputs`, `sumOutputs`, `delta`, and more

Contracts

Expression	Use
`new Contract(args...)`	The output script of a contract. Compare it with an output’s `scriptPubKey` to require that the output pays that contract
`this.tunnel(outputIndex)`	`bool`: the output keeps this input’s script, value, and assets
`tweak(base, fn)`	A key tweaked with covenant `fn`. `tapscript` only

Bytes and numbers

Function	Returns
`a + b`	The two byte strings joined. `cat(a, b)` does the same
`substr(data, offset, size)`, `left(data, n)`, `right(data, n)`	Part of a byte string
`size(data)`, `reverseBytes(data)`	The length, or the bytes in reverse order
`bytes(n)`, `num2bin(n, width)`	An `int` as minimal bytes, or as bytes of a fixed width
`bin2num(data)`	Bytes as an `int`
`abs(n)`, `min(a, b)`, `max(a, b)`, `within(n, low, high)`	Integer helpers. `within` is true for `low <= n < high`
`modExp(base, exp, mod)`	Modular exponentiation
`ecAdd`, `ecMul`, `ecPairing`, `ecMulScalarVerify`, `tweakVerify`	Elliptic curve operations

Integers are BigNums of up to 520 bytes in covenants. +, -, *, /, %, <<, and >> work on int.

Overview

Working with Tapscript

Experimental

Signatures

Hashes

Time

Transaction

Assets

Contracts

Bytes and numbers

​Signatures

​Hashes

​Time

​Transaction

​Assets

​Contracts

​Bytes and numbers

Signatures

Hashes

Time

Transaction

Assets

Contracts

Bytes and numbers