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1099 :: Best way to map with procs?

• willyh (orginal) [2015-04-03T18:08:39+02:00] view original

  Is there a better way to do this:

  var input = "1, 2, 3, 4, 5"
  var lineNums = input.split(",").map(proc (x:string): string = x.strip()).map(proc (x:string): int = parseInt(x))
  Run

  I had expected to be able to do something more like this:

  var lineNums = input.split(",").map(strip).map(parseInt)
  Run

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• Varriount (orginal) [2015-04-03T18:40:30+02:00] view original

  This is currently a consequence of procvar restrictions - outside of their source module, procedures cannot be implicitly converted to procvars. People have suggested that procs have the procvar pragma by default, however Araq has expressed dislike for the idea, apparently because it interferes with default arguments (although how it interferes with them, he still hasn't explained).

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• willyh (orginal) [2015-04-03T19:14:54+02:00] view original

  Thanks. That was clear and pointed me to read up on procvar. I suppose, somewhat naively because I haven't investigated the Nim macro system, I could write a macro to wrapper a function with a procvar'd function to do what I want to do. Something that would look like this in use:

  
  var lineNums = input.split(",").map(#strip).map(#parseInt)
  Run

  where the # symbol is my macro. Thanks again for the quick answer.

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• Jehan (orginal) [2015-04-03T20:42:00+02:00] view original

  This has nothing to do with procvar vs. closure; map expects a closure to begin with and procvars can always be converted to closures, anyway. The problem is that strip has two optional parameters, so it's being treated as a proc(string, bool, bool): string {.closure.} type and map expects a proc(string): string {.closure.} type.

  The following works:

  import strutils
  
  proc mystrip(x: string): string =
    x.strip
  
  var input = "1, 2, 3, 4, 5"
  var lineNums = input.split(",").map(mystrip).map(parseInt)
  echo lineNums
  Run

  Note how everything works out of the box for parseInt.

  If you add a y: bool = false parameter to mystrip, it breaks.

  Ideally, the type inference mechanism should be able to instantiate proc parameters with omitted defaults with a generated proc that instantiates the defaults.

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