Confusing error with static parameters

[Clyybber]

The following snippet errors out with a confusing error.

Example

import strutils

type
  Tile[n: static int] = object
    a: array[n, int]
  Coord = tuple[x, y: int]
  Rule[n: static int] = tuple[c: Coord, t: Tile[n]]
  Discriminator[n: static int] = seq[Rule[n]]
  Tileset[n: static int] = array[n, Discriminator[n]]

proc parseMapHeader(content: static string): seq[string] {.compileTime.} =
  var cols = 0 #When 3 then it is a tilename in the form of ":::NAME"
  for c in content:
    if cols == 3:
      if c == '\n':
        cols = 0
      else:
        result[^1].add c
    elif c == ':':
      inc cols
      if cols == 3:
        result.add ""
    else:
      cols = 0
  for s in mitems(result):
    s = s.strip

#works fine with `tiles: static seq[string]` -> `tiles: seq[string]`
proc parseProb(tiles: static seq[string], tileslen: static int, p: string): Tile[tileslen] =
  discard "TODO"

proc parseMap(tiles: static seq[string], tileslen: static int, content: static string): Tileset[tileslen] =
  var i = 0
  template c: char = content[i]
  for id, name in tiles:
    assert content[i..i+2] == ":::"
    while c != '\n': inc i #Skip one line ':::`name`'
    inc i
    var asciiDefs: array[char, Tile[tileslen]]
    block parseDefs:
      while true:
        block parseSomeDef:
          if c in Letters and content[i+1..i+3] == " = ":
            block parseAsciiDef:
              let oldC = c
              assert content[i+1..i+3] == " = "
              inc i, 4 #Skip "_ = "
              var pStr: string
              while c != '\n':
                pStr.add c
                inc i
              asciiDefs[oldC] = parseProb(tiles, tileslen, pStr)
              inc i #Skip '\n'
              break parseSomeDef
          else:
            break parseDefs

when isMainModule:
  const content = """
:::PillarRoom
A = [Pillar: 1]
"""
  const names = parseMapHeader(content)
  const parsedTileset = parseMap(names, names.len, content)

Current Output

stack trace: (most recent call last)
/home/clyybber/projects/tests/ttt.nim(63, 33)
/home/clyybber/projects/tests/ttt.nim(11, 6) parseMap
/home/clyybber/projects/tests/ttt.nim(11, 6) Error: index out of bounds, the container is empty

Expected Output

Should compile or spit out a more appropriate error message.

Possible Solution

See the comment in the snippet

Additional Information

$ nim -v
Nim Compiler Version 1.0.99

[metagn]

A bit simplified:

type
  Tile[n: static int] = object
    a: array[n, int]
  Coord = tuple[x, y: int]
  Rule[n: static int] = tuple[c: Coord, t: Tile[n]]
  Discriminator[n: static int] = seq[Rule[n]]
  Tileset[n: static int] = array[n, Discriminator[n]]

#works fine with `tiles: static seq[string]` -> `tiles: seq[string]`
proc parseProb(tiles: static seq[string], tileslen: static int, p: string): Tile[tileslen] =
  discard "TODO"

proc parseMap(tiles: static seq[string], tileslen: static int, content: static string): Tileset[tileslen] =
  for id, name in tiles:
    var pStr: string = ""
    discard parseProb(tiles, tileslen, pStr)

when isMainModule:
  const parsedTileset = parseMap(@["a", "b", "c"], 3, "abc")