Iterating over a list with `createCmd` in a script

Questions
1

I often write the following, intuitively thinking that it should work:

forA_ list $ submit party do createCmd

This throws the error:

Couldn't match type ‘Commands (ContractId t0)’ with ‘Script b0’
      Expected type: MyListTemplate -> Script b0
        Actual type: MyListTemplate
                     -> Commands (ContractId t0)

I’ve meanwhile found out what it should be, and I think I understood why that is:

submit party do forA_ list createCmd

But could someone ELI5 (explain like I’m 5) why the former approach doesn’t work?

EDIT:
I suppose the confusing thing is that this actually does work:

forA_ list (\c -> submit party do createCmd c)

So why is submit party do createCmd not the same as \c -> submit party do createCmd c in this case?

1 Like
2

forA_ list $ submit party . createCmd should also work. Your example is equivalent to forA_ list $ \c -> ((submit party) createCmd) c which leads to the type error you are seeing:
submit has type Party -> Commands a -> Script a but the second argument you are applying it to is createCmd not createCmd c which has the wrong type.

submit party $ do forA_ list createCmd has different semantics. It creates all contracts in a single transaction rather than spread out over multiple transactions.

2 Likes
3

Great answer, and truly ELI5 :slight_smile: thanks!