Questions on the current stage of concepts

[ElegantBeef]

Generic procedures are just splendid, this seems to be a bug that it fails to 
validate that it's possible to instantiate the generic after sem checking
    
    
    type
      Addable = concept c, type T
        c + c is T
      
      Coll = concept c
        typeof(c.items)
      
      AddableColl[T] = concept c
        T is typeof(c.items)
        typeof(c.items) is Addable
        c is Coll
    
    
    proc sum[T](nums: AddableColl[T]): T =
      for num in nums.items:
        result += num
    
    echo @[0, 1, 2].sum()
    echo @["0", "1", "2"].sum()
    
    
    Run

Is an old style working version of what you're after.