Concatenation of seq and array?

[haoliang]

although this thread is old, i still wanna add another use case: 
[foldl](https://nim-lang.org/docs/sequtils.html#foldl.t%2C%2C%2C)
    
    
    let
      numbers = @[0, 8, 1, 5]
      digits = foldl(numbers, a & (chr(b + ord('0'))), "")
    assert digits == "0815"
    
    
    Run