compiler

Overview ¶

Package equity provides a compiler for Chain's Equity contract language.

A contract is a means to lock some payment in the output of a transaction. It contains a number of clauses, each describing a way to unlock, or redeem, the payment in a subsequent transaction. By executing the statements in a clause, using contract arguments supplied by the payer and clause arguments supplied by the redeemer, nodes in a Chain network can determine whether a proposed spend is valid.

The language definition is in flux, but here's what's implemented as of late May 2017.

program = contract*

contract = "contract" identifier "(" [params] ")" "locks" identifier "{" clause+ "}"

  The identifier after "locks" is a name for the value locked by
  the contract. It must be unlocked or re-locked (with "unlock"
  or "lock") in every clause.

clause = "clause" identifier "(" [params] ")" ["requires" requirements] "{" statement+ "}"

  The requirements are blockchain values that must be present in
  the spending transaction in order to spend the value locked by
  the earlier transaction. Each such value must be re-locked
  (with "lock") in its clause.

statement = verify | unlock | lock

verify = "verify" expr

  Verifies that boolean expression expr produces a true result.

unlock = "unlock" expr

  Expr must evaluate to the contract value. This unlocks that
  value for any use.

lock = "lock" expr "with" expr

  The first expr must be a blockchain value (i.e., one named
  with "locks" or "requires"). The second expr must be a
  program. This unlocks expr and re-locks it with the new
  program.

requirements = requirement | requirements "," requirement

requirement = identifier ":" expr "of" expr

  The first expr must be an amount, the second must be an
  asset. This denotes that the named value must have the given
  quantity and asset type.

params = param | params "," param

param = idlist ":" identifier

  The identifiers in idlist are individual parameter names. The
  identifier after the colon is their type. Available types are:

    Amount; Asset; Boolean; Hash; Integer; Program; PublicKey;
    Signature; String; Time

idlist = identifier | idlist "," identifier

expr = unary_expr | binary_expr | call_expr | identifier | "(" expr ")" | literal

unary_expr = unary_op expr

binary_expr = expr binary_op expr

call_expr = expr "(" [args] ")"

  If expr is the name of an Equity contract, then calling it (with
  the appropriate arguments) produces a program suitable for use
  in "lock" statements.

  Otherwise, expr should be one of these builtin functions:

    sha3(x)
      SHA3-256 hash of x.
    sha256(x)
      SHA-256 hash of x.
    size(x)
      Size in bytes of x.
    abs(x)
      Absolute value of x.
    min(x, y)
      The lesser of x and y.
    max(x, y)
      The greater of x and y.
    checkTxSig(pubkey, signature)
      Whether signature matches both the spending
      transaction and pubkey.
    concat(x, y)
      The concatenation of x and y.
    concatpush(x, y)
      The concatenation of x with the bytecode sequence
      needed to push y on the ChainVM stack.
    before(x)
      Whether the spending transaction is happening before
      time x.
    after(x)
      Whether the spending transaction is happening after
      time x.
    checkTxMultiSig([pubkey1, pubkey2, ...], [sig1, sig2, ...])
      Like checkTxSig, but for M-of-N signature checks.
      Every sig must match both the spending transaction and
      one of the pubkeys. There may be more pubkeys than
      sigs, but they are only checked left-to-right so must
      be supplied in the same order as the sigs. The square
      brackets here are literal and must appear as shown.

unary_op = "-" | "~"

binary_op = ">" | "<" | ">=" | "<=" | "==" | "!=" | "^" | "|" |
      "+" | "-" | "&" | "<<" | ">>" | "%" | "*" | "/"

args = expr | args "," expr

literal = int_literal | str_literal | hex_literal