Is there a way to display the "type" of a function or data type in Daml?

Questions
1

Is there a way to display the “type” of a function or data type in Daml - equivalent to typeof in JavaScript or :t functionName in Haskell?

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2

typeof in JS and :t in Haskell are quite different. Do you mean in Daml Studio, in the REPL, or as some form of runtime reflection?

3

In Daml Studio, one can already see the type by hovering over the function or data type.
I’m looking to know if there’s a way to do it in:

  1. REPL
  2. runtime reflection
4

Yes, kind of …

In the repl, you can use holes, as you would in a source file, like so:

daml> import DA.Assert ((===))
daml> foldl _ _ ["Hello", "world", "!"] === [(0, "Hello"), (1, "world"), (2, "!")]

File:     <string>
Hidden:   no
Range:    1:7-1:8
Source:   typecheck
Severity: DsError
Message: 
  <string>:1:7: error:
  • Found hole: _ : [(Int, Text)] -> Text -> [(Int, Text)]
  • In the first argument of ‘foldl’, namely ‘_’
  In the first argument of ‘(===)’, namely
  ‘foldl _ _ ["Hello", "world", "!"]’
  In the first argument of ‘show’, namely
  ‘(foldl _ _ ["Hello", "world", "!"]
  === [(0, "Hello"), (1, "world"), (2, "!")])’

So you can see in the error message, it tells you the type (after “Found hole”).
It won’t work in every case, but for functions it does the job.

5

And just to make this explicit, there is no runtime reflection of types.

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