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9024 :: Why doesn't echo have tag WriteIOEffect?

• RainbowAsteroids (orginal) [2022-03-20T08:00:01+01:00] view original

  The following code:

  {.push tags: [].}
  
  proc hello() =
    stdout.write "Hello, world!\n"
  
  when isMainModule:
    hello()
  Run

  has an error at compile time, which makes sense, because hello() should be annotated with the WriteIOEffect. However,

  {.push tags: [].}
  
  proc hello() =
    echo "Hello, world!"
  
  when isMainModule:
    hello()
  Run

  has no such compile time error, despite doing pratically the same thing. When looking at the documentation, echo's routine signature explicitly states that it has no tags. Why?

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• Araq (orginal) [2022-03-20T08:53:02+01:00] view original

  Because it would be annoying, echo is often used for debugging. And echo should not have a side-effect either and debugEcho should be deprecated.

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• RainbowAsteroids (orginal) [2022-03-20T09:07:54+01:00] view original

  So what's the point of having an effect system if the most common way to write to stdout is going to be an exception to the rule?

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• Araq (orginal) [2022-03-20T09:16:55+01:00] view original

  The effect system consists of more than of .tags tracking, .tags are both the simplest variant of Nim's effect system and the most useless. In my experience.

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• federico3 (orginal) [2022-03-21T20:59:56+01:00] view original

  Dedicated effects for debugging+logging+metrics could be useful. Most of the time these are seen as "out-of-band" activities.

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