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926 :: range logic problem

• CharlesH (orginal) [2015-02-25T20:44:31+01:00] view original

  The code:

  type
     Rows   =  0..32
     Cols   =  0..32
     Coord   =  tuple[row: Rows, col: Cols]
     . . .
     Cell  =  object
        doors :  Doors
     Grid  =  ref   GridObj
  
  . . .
  
  proc  cN(g: Grid, row: Rows, col: Cols): Coord  =
     try:
        let   c: Coord =  (row: row - 1, col: col)
        result   =   c
     except:
        raise newException(IndexError, "Attempt to move too far North")
  Run

  results in error:

  . . . (60, 24) Error: type mismatch: got (tuple[row: range -1..31(int), col: Cols]) but expected 'Coord'

  Process terminated with exit code 256

  I first tried to avoid this with an if test. How should I handle this? All I can think of is expanding the range to include an illegal value.

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• def (orginal) [2015-02-25T20:53:52+01:00] view original

  You should ensure that no invalid values can happen, by somehow preventing them, for example:

  let newRow: Rows = max(row-1, 0)
  result = (newRow, col)
  # Or even shorter:
  result = (Rows(max(row - 1, 0)), col)
  Run

  I guess using 3 spaces for indentation is a compromise between 2 and 4? :P

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• LeuGim (orginal) [2015-02-25T21:00:35+01:00] view original

  As def said, or you can cast the expression to Rows:

  let   c: Coord =  (row: Rows(row - 1), col: col)
  Run

  or use in context where it's definitely valid and compiler can see it:

  if row > 0:
    let   c: Coord =  (row: row - 1, col: col)
    result   =   c
  Run

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• CharlesH (orginal) [2015-02-26T01:01:14+01:00] view original

  So I tried:

  proc  cN(g: Grid, row: Rows, col: Cols): Coord  =
     if row > 0:
        let   c: Coord =  (row: row - 1, col: col)
        result   =   c
     else:
        raise newException(IndexError, "Attempt to move too far North")
  Run

  and got:

  . . .(60, 24) Error: type mismatch: got (tuple[row: range -1..31(int), col: Cols]) but expected 'Coord'

  Process terminated with exit code 256

  That's the "let" statement.

  However, combining suggestions:

  proc  cN(g: Grid, row: Rows, col: Cols): Coord  =
     if row > 0:
        let   c: Coord =  (row: Rows(row - 1), col: col)
        result   =   c
     else:
        raise newException(IndexError, "Attempt to move too far North")
  Run

  lets me get to a routine I'm still writing that will use this proc. (Currently the message is "Invalid Indentation", but what it really means is that the proc ended before the body of a for statement.)

  Thanks.

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• LeuGim (orginal) [2015-02-26T06:15:24+01:00] view original

  Indeed, doesn't work with just if.

  It seems the best is just to declare the argument as 1..32, what it is intended to be. And this works.

  proc  cN(g: Grid, row: 1..32, col: Cols): Coord  =
     if row > 0:
        let   c: Coord =  (row: Rows(row - 1), col: col)
        result   =   c
     else:
        raise newException(IndexError, "Attempt to move too far North")
  
  let r: Rows = 2
  echo cN(nil, r, 7).repr
  Run

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