I'm confused as to how def and let bind variables differently. Can someone explain to me why this works:
(def leven
(memoize
(fn [x y]
(cond (empty? x) (count y)
(empty? y) (count x)
:else (min (+ (leven (rest x) y) 1)
(+ (leven x (rest y)) 1)
(+ (leven (rest x) (rest y)) (if (= (first x) (first y)) 0 1)))))))
But when I try to declare the function as let it fails to compile:
(def leven
(let [l (memoize (fn [x y]
(cond (empty? x) (count y)
(empty? y) (count x)
:else (min (+ (l (rest x) y) 1)
(+ (l x (rest y)) 1)
(+ (l (rest x) (rest y)) (if (= (first x) (first y)) 0 1))))))]
(l x y)))
EDIT: This works, using the technique showed by Ankur.
(defn leven [x y]
(let [l (memoize (fn [f x y]
(cond (empty? x) (count y)
(empty? y) (count x)
:else (min (+ (f f (rest x) y) 1)
(+ (f f x (rest y)) 1)
(+ (f f (rest x) (rest y)) (if (= (first x) (first y)) 0 1))))))
magic (partial l l)]
(magic x y)))
Below is such an example to do what you have asked for. I am using factorial just for the sake of simplicity and added println in factorial to make sure the memoization is working fine
(let [fact (memoize (fn [f x]
(println (str "Called for " x))
(if (<= x 1) 1 (* x (f f (- x 1))))))
magic (partial fact fact)]
(magic 10)
(magic 11))
First calculate factorial of 10 and then 11 in which case it should not again call factorial for 10 till 1 as that has been memoized.
Called for 10
Called for 9
Called for 8
Called for 7
Called for 6
Called for 5
Called for 4
Called for 3
Called for 2
Called for 1
Called for 11
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