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3192 :: Why does this not compile, and how can I fix it?

• Stefan_Salewski (orginal) [2017-09-23T19:30:46+02:00] view original

  import strutils
  
  type
    App = ref object of RootObj
      i: int
  
  proc isDigit(app: App) =
    discard
  
  macro xconnect(widget: RootRef; signal: string; p: typed; arg: typed; ignoreArg: bool): untyped =
    discard
  
  proc main =
    let app: App = nil
    xconnect(app, "activate", isDigit, "", true)
  
  main()
  
  #
  # nim -v
  # Nim Compiler Version 0.17.2 (2017-09-08) [Linux: amd64]
  # Copyright (c) 2006-2017 by Andreas Rumpf
  # $ nim c button.nim
  # button.nim(15, 11) Error: type mismatch: got (App, string, proc (app: App){.noSideEffect, gcsafe, locks: 0.} | proc (c: char): bool{.noSideEffect, gcsafe, locks: 0.} | proc (s: string): bool{.noSideEffect, gcsafe, locks: 0.}, string, bool)
  # but expected one of:
  # macro xconnect(widget: RootRef; signal: string; p: typed; arg: typed; ignoreArg: bool): untyped
  
  Run

  And this is how the error message for a real application looks:

  http://ssalewski.de/tmp/AQ.txt

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• LeuGim (orginal) [2017-09-23T20:39:09+02:00] view original

  You can fix it by disambiguating the passed proc name, isDigit -> module_name.isDigit (you see in the error message, that this is the cause). Yet you can turn the corresponding parameter into untyped.

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• Stefan_Salewski (orginal) [2017-09-23T20:51:08+02:00] view original

  No, I have not seen from the error message that module name prefix was necessary.

  I have switched parameter type for handler proc from untyped to typed, as Yardanico told me that typed parameter is necessary to be able to investigate parameter list of handler proc. After changing parameter type to typed, I got that strange error messages and it took me some hours to find out why it was not working with typed parameter. The actual connect macro is this: https://github.com/StefanSalewski/gintro/blob/master/gintro/gimpl.nim#L38 and initially I had the feeling that I did something wrong in the macro. (Araq told me to convert it by using the AST API instead string hacks, I will do that at some time, but it will not help for this issue.) This issue will confuse GTK users for sure.

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• LeuGim (orginal) [2017-09-23T22:16:02+02:00] view original

  Well, maybe that's not so clear really, the logic that I meant about error message is that it has a union type for the 3rd argument in "got" section and not a concrete type, which obviously means compiler could not detect one concrete binding for this argument; yet in the type for the argument there are listed signatures for both your module's isDigit and strutils' isDigit, and strutils is imported. With qualified name (or having renamed your proc) you get rid of ambiguity and make the arg's type concrete; otherwise, by turning the parameter into untyped, you allow unbound identifiers.

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