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4998 :: Macro to create a dictionary (table) like in python!

• mrhdias (orginal) [2019-07-08T23:36:27+02:00] view original

  Is it possible to create a dictionary like python by typing only:

  var a = {"key_1": "value_1", "key_2": "value_2"}
  Run

  Instead of?

  var a = {"key_1": "value_1", "key_2": "value_2"}.toTable
  Run

  or something similar to what is used by sequences:

  var x = @[1, 2, 3]
  
  var a = %{"key_1": "value_1", "key_2": "value_2"}
  Run

  It reminds me Perl arrays (@) and hashes (%).

  How to make a macro to implement the "%" before "{}"?

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• solo989 (orginal) [2019-07-09T00:43:37+02:00] view original

  Couldn't render post #31327.

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• mrhdias (orginal) [2019-07-09T15:10:50+02:00] view original

  Great. Works. Thank you.

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• zevv (orginal) [2019-07-09T19:32:03+02:00] view original

  
  proc `%`[T,G,H](a : array[T,(G,H)]) : Table[G,H] =
  Run

  wow, I had to read that three times before it sank in

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• mratsim (orginal) [2019-07-10T07:17:24+02:00] view original

  The T should probably be renamed N for convention, possibly tagging it with static int as well.

  Also it's true that {key: value} syntax creating an array of tuples is not well documented/visible.

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• juancarlospaco (orginal) [2019-07-10T13:44:09+02:00] view original

  is sugar, so a literal is also possible.

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• treeform (orginal) [2019-07-10T22:31:07+02:00] view original

  I think using @ instead of the % is perfect. Its just like the array syntax.

  
  var a = @[1, 2, 3]
  var b = @{"key_1": "value_1", "key_2": "value_2"}
  Run

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• SolitudeSF (orginal) [2019-07-11T00:11:53+02:00] view original

  {} is a sugar for array of tuples, so @ already works with it by just making a sequence.

  echo @{"key_1": "value_1", "key_2": "value_2"}
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  results in

  
  @[("key_1", "value_1"), ("key_2", "value_2")]
  Run

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• cblake (orginal) [2019-07-11T00:12:19+02:00] view original

  I would have to agree with @. +1 vote.

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• mrhdias (orginal) [2019-07-12T18:32:18+02:00] view original

  What prevents it from being used only like this without "%", "@" or "toTable"?

  var a = {"key_1": "value_1", "key_2": "value_2"}
  Run

  It's simple and everyone understands!

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• miran (orginal) [2019-07-12T18:58:50+02:00] view original

  Couldn't render post #31397.

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• cblake (orginal) [2019-07-12T19:42:51+02:00] view original

  These association lists, often abbreviated "alist", get a lot of play in lisp, but also OCaml, Haskell, etc.. https://en.wikipedia.org/wiki/Association_list

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• zevv (orginal) [2019-07-12T20:29:37+02:00] view original

  Github pull request: https://github.com/nim-lang/Nim/pull/11702.

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• mrhdias (orginal) [2019-07-13T15:53:09+02:00] view original

  I did this small test and I don't see any problems or incompatibility. Can someone show me where the use of the "%" can fail? Can someone show me an example where the "%" is used in JSON as in tables "%{}"?

  import tables
  from strutils import `%`
  import json
  
  proc `%`[T,G,H](a : array[T,(G,H)]) : Table[G,H] =
      a.toTable()
  
  # Table
  var h = %{"key_1": "value_1", "key_2": "value_2"}
  echo h
  echo h["key_1"]
  
  # JSON
  var j = %*{"key_1": "value_1", "key_2": "value_2"}
  echo j
  echo j["key_1"]
  Run

  Result:

  
  $ nim c -r test.nim
  Hint: operation successful (34378 lines compiled; 8.349 sec total; 46.828MiB peakmem; Debug Build) [SuccessX]
  Hint: /home/hdias/Downloads/test  [Exec]
  {"key_1": "value_1", "key_2": "value_2"}
  value_1
  {"key_1": "value_1", "key_2": "value_2"}
  "value_1"
  Run

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