How to convert range types 'a'..'z'?

[alexeypetrushin]

How to convert range types? Expressions like `v('a'..'z')` doesn't work.

[Playground](https://play.nim-lang.org/#ix=3yJ4)
    
    
    import sequtils
    
    type Check* = tuple
      priority: 'a'..'c'
      message:  string
    
    converter to_check*(check: (char, string)): Check =
      (check[0], check[1])
    converter to_check*(check: seq[(string, string)]): seq[Check] =
      messages.map(to_check)
    
    var checks: seq[Check]
    checks.add ('a', "some")
    
    
    Run