import tables, strutils

proc getFrequencies() : CountTable[string] =
  let wordFrequencies = initCountTable[string]() # <-- this should be var

  for line in open("example1.nim").lines():
    for word in line.split(", "):
      wordFrequencies.inc(word)

  return wordFrequencies

let wordFrequencies = getFrequencies()
echo "The most frequent word is '", wordFrequencies.largest, "'"
echo "The frequencies are '", wordFrequencies, "'"