How to get the name of a template or data type

Questions
1

Hello,
Let’s say that I have the following template:

template Hello
  with
    owner: Party
  where
    signatory owner

How can I print only the template name once I create it in a script? Is there something similar like the Haskell’s typeOf function?

2

There is in the form of TypeRep, but the function to print those type representations is a dev-only feature, meaning it’s only available in Daml-LF 1.dev. Might be of use in a test script, but cannot be used in a package that you deploy to the ledger:

module Main where

import Daml.Script

template Hello
  with
    owner: Party
  where
    signatory owner

ttrFromCid : forall t . (Template t) => ContractId t -> TemplateTypeRep
ttrFromCid x = templateTypeRep @t

setup : Script ()
setup = script do
  owner <- allocatePartyWithHint "owner" (PartyIdHint "owner")

  helloCid <- submit owner do
    createCmd Hello with ..

  Some hello <- queryContractId owner helloCid

  let tr = ttrFromCid helloCid

  debug (templateTypeRepToText tr)

Requires in daml.yaml:

build-options:
  - --target=1.dev

You’ll get output (in the IDE):

Trace: 
  "-homePackageId-:Main:Hello"
3 Likes
3

Thanks @bernhard,
Why is this limited to dev only? I would like to have this not only in dev environment.

4

Adding stable features has ongoing cost as Daml has strong backwards compatibility guarantees. Whether this particular feature has enough value is not clear. We have opened a ticket here for discussion: Investigate impact/need of providing template names in Daml Script · Issue #19604 · digital-asset/daml · GitHub

1 Like