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1660 :: arbitrary-syntax DSL without using strings

• sstirlin (orginal) [2015-09-23T02:03:38+02:00] view original

  I'm trying to duplicate numpy syntax for array slicing, i.e. I want something like this

  var arr2 = arr[2:0:2, 3:0:1, 2:0:2]
  Run

  I can get this to work if I pass the argument as a string, i.e. var arr2 = arr["2:0:2, 3:0:1, 2:0:2"] by using the following macro (simplified)

  macro `[]`[T](arr: ArrayView[T], e: string): expr =
      
      var args = split(e.strVal, ",")
      var code = $arr & "["
      
      for i in 0.. <len(args):
          var ixs = split(args[i], ":")
          for j in 0.. <len(ixs):
              if j != len(ixs)-1:
                  code = code & ixs[j] & ".. "
              else:
                  code = code & ixs[j]
          if i != len(args)-1:
              code = code & ","
      
      code = code & "]"
      parseExpr(code)
  Run

  However, is there a way to remove the quotes from the call? In other words, I don't want to call using a string "2:0:2, 3:0:1, 2:0:2", but instead I want to call using 2:0:2, 3:0:1, 2:0:2.

  I realize that the latter is not a valid expression. However, I'm hoping that there's something in the macro system that can be called when parsing fails (so that I can parse it myself) or when the parsed expression does not match the signature of any known proc.

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• def (orginal) [2015-09-23T02:54:57+02:00] view original

  : is a special token in Nim, so you can't use it there. With another symbol it should work. You'll end up parsing this AST using the macros module:

  import macros
  
  dumpTree:
    var arr2 = arr[2!0!2, 3!0!1, 2!0!2]
  Run

  
  StmtList
    VarSection
      IdentDefs
        Ident !"arr2"
        Empty
        BracketExpr
          Ident !"arr"
          Infix
            Ident !"!"
            Infix
              Ident !"!"
              IntLit 2
              IntLit 0
            IntLit 2
          Infix
            Ident !"!"
            Infix
              Ident !"!"
              IntLit 3
              IntLit 0
            IntLit 1
          Infix
            Ident !"!"
            Infix
              Ident !"!"
              IntLit 2
              IntLit 0
            IntLit 2
  Run

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• Araq (orginal) [2015-09-23T03:07:59+02:00] view original

  1. Use x.add(y) instead of x = x & y.
  2. In addition to what def- said, here are more suggestions:

  x[0..1|2, 3..4|4]
  x[0..1|+2, 3..4|-4]
  
  x[0\0\2]
  x[0~0~2, 0~3~4]
  Run

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• sstirlin (orginal) [2015-09-23T19:41:12+02:00] view original

  Interesting - I tried all of those syntax options previously (great minds think alike :). After some use, however, they started to make my eyes bleed. Here are various things that I tried:

  #var revarr = arr[2|0|-1, 3|0|-1, 2|0|-1] # compiler yells that |- is not an operator!
  var revarr = arr[2|0| -1, 3|0| -1, 2|0| -1]
  
  var revarr = arr[2..0| -1, 3..0| -1, 2..0| -1]
  
  var revarr = arr[2..0.. -1, 3..0.. -1, 2..0.. -1]
  
  var revarr = arr[(2,0,-1), (3,0,-1), (2,0,-1)]
  Run

  Minus signs makes things particularly ugly because I need to separate them with a space. I guess I could always explicitly define a separate operator, e.g. |-.

  More importantly, I want more syntactic sugar like we see in numpy:

  var revarr = arr[2|0| -1, |, 2|0| -1]
  var revarr = arr[..., 2|0| -1]
  Run

  It doesn't seem to be possible to define an operator | that takes zero args, and likewise for .... Any suggestions?

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• Araq (orginal) [2015-09-23T20:51:41+02:00] view original

  Well yes, I would introduce |+ and |- for positive and negative steps (as well as ..|+ and ..|- for nicer composition). IMHO it's more beautiful than Python's ':'. ;-)

  It doesn't seem to be possible to define an operator | that takes zero args, and likewise for .... Any suggestions?

  I would use const all = 0..high(int):

  arr[all, 2..|-1]
  
  Run

  (Or maybe the underscore: arr[_, 2..|-1])

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• sstirlin (orginal) [2015-09-23T22:47:57+02:00] view original

  Sweet. I like that. Thanks!

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