I wrote this yesterday, converting it as best I could from Python:
(let ((l (length word)) (res '()))
(for (i 0 (- l 1)) (push (replace (nth i (string word)) (string word) "") res -1)) ; deletion
(for (i 0 (- l 2)) (push (swap i (+ i 1) (string word)) res -1)) ; transposition
(for (i 0 (- l 1)) (for (c (char "a") (char "z"))
(push (replace (nth i (string word)) (string word) (char c)) res -1) ; alteration
(push (replace (nth i (string word)) (string word) (string (char c) (nth i (string word)) )) res -1))) ; insertion
res))
The idea was to take a word and to generate a set of most of the possible single-letter modifications of that word. So given "newlisp", you'd get deletions: "ewlisp" "nwlisp" "nelisp"..., transpositions: "enwlisp" "nwelisp" ..., insertions: "anewlisp" "bnewlisp" ..., and alterations: "aewlisp" "bewlisp"....
Lutz said I was using 'string casts' - I think he meant those
The function (edits1 word) is entered with 'word' already being a string. This means we don't need the first 'string' cast in 'replace'. We still need the second cast, because we want 'replace' to be non-destructive, as we need the same word in following 'replace' statements again:
(for (i 0 (- l 1))
(push (replace (nth i (string word)) (string word) "") res -1))
; leaving out one cast and implicit indexing
(for (i 0 (- l 1))
(push (replace (word i) (string word) "") res -1))
This is still the same logic as before but slightly shorter and faster.
But here is another approach for extracting the single letters using the select function and much faster:
(for (i 0 (- l 1))
(push (select word (replace i (sequence 0 (- l 1)))) res -1))
The 'replace' takes out one number of (0 1 2 3 4 5 ...) then uses the remaining as a parameter to the 'select' statement.
That's clever! It's surprising that it's so much faster, too.
Thanks!