Last statement in a do block must be an expression?

Mod note: As of SDK 1.5.0 Scenarios have been superseded by the more powerful Daml Script. We now recommend using that for all purposes. For more information, and to learn how to use Script please check out @Andreas’ post on our blog.

I am hitting a snag in the scenario. I hope you can help pinpoint the problem

example = scenario do

  alice <- getParty "Alice"
  bob <- getParty "Bob"
  let citizenkey = CitizenKey with citizen = alice ; id = "1"
  let citizeninfo = CitizenInfo with  citizendetail1 = "Text1" ; citizendetail2 ="Text2" ; citizendetail3 = "Text3" 

  submit alice do 
    create CitizenRegistration with registrationCid = citizenkey; registrationData = citizeninfo

 
  let citizenkey = CitizenKey with citizen = bob ; id = "2" 
  let citizeninfo = CitizenInfo with  citizendetail1 = "Text1" ; citizendetail2 ="Text2" ; citizendetail3 = "Text3" 

  bobregistration <- submit bob do 
    create CitizenRegistration with 
      registrationCid = citizenkey; registrationData = citizeninfo

I trying to understand the correct format for

     bobregistration <- submit bob do 
    create CitizenRegistration with 
      registrationCid = citizenkey; registrationData = citizeninfo

It gives me the following error

error:
    The last statement in a 'do' block must be an expression
      bobregistration <- submit
                           bob
                           do create
                                CitizenRegistration
                                  {registrationCid = citizenkey, registrationData = citizeninfo}typecheck

Hey @bartcant. It looks to me like you need a return statement at the end of your scenario. Without a return statement, you won’t be able to return the result for both Alice and Bob’s registration.

example = scenario do

  alice <- getParty "Alice"
  bob <- getParty "Bob"
  let citizenkey = CitizenKey with citizen = alice ; id = "1"
  let citizeninfo = CitizenInfo with  citizendetail1 = "Text1" ; citizendetail2 ="Text2" ; citizendetail3 = "Text3" 

  aliceRegistration <- submit alice do  create CitizenRegistration with registrationCid = citizenkey; registrationData = citizeninfo

  let citizenkey = CitizenKey with citizen = bob ; id = "2" 
  let citizeninfo = CitizenInfo with  citizendetail1 = "Text1" ; citizendetail2 ="Text2" ; citizendetail3 = "Text3" 

  bobRegistration <- submit bob do create CitizenRegistration with registrationCid = citizenkey; registrationData = citizeninfo
  return(aliceRegistration, bobRegistration)

That’s right. It looks like formatting of the do in

bartcant:

bobregistration <- submit bob do

is fine but the compiler is complaining about the top level scenario:

bartcant:

example = scenario do

As @jamesljaworski85 pointed out, the last statement of a do can’t be a <- (or let) binding. However it could be something other than return if it has the right type, e.g. a create.