For debug re wrote the code, then this got compiled successfully. Wired.
> Nim Compiler Version 1.2.0 [Windows: amd64]
import algorithm, sequtils, strutils, tables
proc disorganize(books: seq[string]): seq[string] =
let step1 = books.mapIt((b :it, t: it.toCountTable))
let step2 = step1.sortedByIt((
it.t['A'] + it.t['a'],
it.t['E'] + it.t['e'],
it.t['I'] + it.t['i'],
it.t['O'] + it.t['o'],
it.t['U'] + it.t['u'],
it.b.reversed.join
))
let step3 = step2.mapIt(it.b)
return = step3
stdout.writeLine stdin.readAll.split("\n").disorganize.join("\n")
Run