Although it can't hurt, I don't think `train` comes close to
dominating the time?
Through the sophisticated profiling technique of commenting-out `or`
branches in `correct`, I got the sense that the third one is the
issue:
(define (correct m s)
(let ([best-known (λ (xs) (best-known m xs))])
(or (best-known (list s))
(best-known (edits1 s))
(best-known (append-map edits1 (edits1 s))) <-- if reached, very slow
s)))
real 0m16.527s
user 0m14.554s
sys 0m1.859s
(define (correct m s)
(let ([best-known (λ (xs) (best-known m xs))])
(or (best-known (list s))
(best-known (edits1 s))
(best-known (edits2 m s)) ;; what I posted yesterday
s)))
real 0m9.807s
user 0m9.463s
sys 0m0.266s
(define (correct m s)
(let ([best-known (λ (xs) (best-known m xs))])
(or (best-known (list s))
(best-known (edits1 s))
;; (best-known (edits2 m s)) ;; skip it entirely
s)))
real 0m2.074s
user 0m1.708s
sys 0m0.184s
p.s. `best-known` = combining `best` and `known` into a single pass for/fold:
;; Given a hash map and a list of words, returns
;; one of the words with the highest frequency.
;; Given an empty list returns #f
(define (best-known ht xs)
(car (for*/fold ([best (cons #f 0)])
([x (in-list xs)]
[v (in-value (hash-ref ht x #f))] ;; should default be 1?
#:when v)
(if (> v (cdr best)) (cons x v) best))))
... which I thought might be faster but wasn't significant.
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