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8279 :: What is the difference between `quote do:` and just `quote:`?

• xigoi (orginal) [2021-07-28T16:37:03+02:00] view original

  I posed this question as an aside in this thread and nobody answered; @dom96 was also wondering.

  Why do macros often use the construct quote do:, when quote: alone seems to work just fine?

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• Araq (orginal) [2021-07-28T16:58:32+02:00] view original

  This works:

  import macros
  
  macro m(x: untyped) =
    result = newStmtList()
    result.add quote do:
      echo `x`
  
  m:
    "hi"
  Run

  And this doesn't:

  import macros
  
  macro m(x: untyped) =
    result = newStmtList()
    result.add quote:
      echo `x`
  
  m:
    "hi"
  Run

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• Araq (orginal) [2021-07-28T17:00:37+02:00] view original

  The do here binds the body to the quote whereas otherwise it's bound to the add operation which is clearly not what we want.

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• dom96 (orginal) [2021-07-30T00:25:46+02:00] view original

  Thanks for posting this question and thanks for the answer.

  I must say, I am surprised that this minor syntax difference is the reason why quote is used with a do so much. I wish we'd gone with:

  import macros
  
  macro m(x: untyped) =
    result = newStmtList()
    result.add(
      quote: echo `x`
    )
  
  m:
    "hi"
  Run

  And been done with it. In fact, why doesn't this work?

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