Why is ApplicativeDo not doing it's magic?

Questions
1

I’ve got {-# LANGUAGE ApplicativeDo #-} at the top of my file. In a script i have

  submit issuer do
    exerciseCmd eqA_Alice Airdrop with
      quantity = 1000.0
      reference = None
    exerciseCmd eqB_Alice Airdrop with
      quantity = 1000.0
      reference = None

The first exerciseCmd is underlined with error

    • No instance for (Action Commands) arising from a do statement
    • In a stmt of a 'do' block:
        exerciseCmd eqA_Alice Airdrop {quantity = 1000.0, reference = None}
      In the second argument of ‘submit’, namely
        ‘do exerciseCmd
              eqA_Alice Airdrop {quantity = 1000.0, reference = None}
            exerciseCmd
              eqB_Alice Airdrop {quantity = 1000.0, reference = None}’
      In a stmt of a 'do' block:
        _ <- submit
               issuer
               do exerciseCmd
                    eqA_Alice Airdrop {quantity = 1000.0, reference = None}
                  exerciseCmd eqB_Alice Airdrop {quantity = 1000.0, reference = None}typecheck

What am I doing wrong?

1 Like
2

ApplicativeDo is a bit picky because it does syntactic matching on the expression before typechecking. It really wants the last line to be either pure or return. This is documented in Module Daml.Script — Daml SDK 1.18.0 documentation

So if you change your example to the following it should work.

submit issuer do
  exerciseCmd …
  c <- exerciseCmd …
  pure c
1 Like
3

Of course, I had forgotten that, thanks. I was even on that page and didn’t read the paragraph to the end :man_facepalming: