Can I create a smart contract from inside another smart contract in LIGO?

Question

Through a parent contract, I want to be able to originate multiple child contracts. How can I do this in LIGO?

Answer 1

Unfortunately, Tezos.create_contract does not work well in practice. It only works if the child contract is extremely simple. The child code must either be written entirely inside the Tezos.create_contract call, or all of the definitions it uses must be [@inline]'d. If not all definitions are inlined, you will get the somewhat cryptic error "Not all free variables could be inlined in Tezos.create_contract usage."

A better alternative should be provided in some future Ligo version. Hopefully soon-ish.

In the meantime there is a workaround: compile your child contract separately, and use inline %Michelson with CREATE_CONTRACT, possibly using #include to include the compiled .tz file. Here is an example in Cameligo:

type child_storage = unit

type create_contract_args =
  [@layout:comb]
  (* order matters because we will cross the Michelson boundary *)
  { delegate : key_hash option;
    balance : tez;
    storage : child_storage }

type create_contract_result =
  [@layout:comb]
  { operation : operation;
    address : address }

[@inline] let create_contract =
  [%Michelson ({|{ UNPAIR 3;
                   CREATE_CONTRACT
#include "./child.tz"
;
                   PAIR
                   }|} : create_contract_args -> create_contract_result)]

let main (_ : unit * unit) : operation list * unit =
  let {operation; address = _} =
    create_contract { delegate = (None : key_hash option);
                      balance = Tezos.get_amount ();
                      storage = () } in
  ([operation], ())

Answer 2

Check the contract factory example: https://ligolang.org/docs/tutorials/inter-contract-calls/inter-contract-calls/#contract-factories

The code they are using is available here: https://gitlab.com/ligolang/ligo/-/blob/dev/gitlab-pages/docs/tutorials/inter-contract-calls/examples/contracts/ligo/CreateAndCall.ligo