In readline unix-word-rubout (C-w) deleted one word to the left of the cursor, leaving the cursor in the position of the first letter of that word. (123 45|6 -> 123 |6)
However, in ghci, it deletes the whitespaces before the word as well. (123 45|6 -> 123|6)
Haskeline differs from readline in C-w behaviour:
123 45|6->123 |6)123 45|6->123|6)