faststr.nim

var str = newString(1001*3 + 1001*801*3 + 1001*801*501*3)

var i = 0
for foo in 0..100:
  str[i] = 'f'
  inc i
  str[i] = 'o'
  inc i
  str[i] = 'o'
  inc i
  for bar in 0..800:
    str[i] = 'b'
    inc i
    str[i] = 'a'
    inc i
    str[i] = 'r'
    inc i
    for baz in 0..500:
        str[i] = 'b'
        inc i
        str[i] = 'a'
        inc i
        str[i] = 'z'
        inc i

nim c -d:danger faststr.nim
time ./faststr 
1.30 real         0.45 user         0.33 sys