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Commit 6ed8970

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stuarthallowaystuarthalloway
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idiomatic Clojure: use letfn and zero?
1 parent db3add1 commit 6ed8970
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‎examples/functional.clj‎

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+13-36Lines changed: 13 additions & 36 deletions
Original file line numberDiff line numberDiff line change
@@ -11,49 +11,26 @@
1111
; END: stack-consuming-fibo
1212

1313
; START: tail-fibo
14-
; also bad: still consumes stack!
1514
(defn tail-fibo [n]
16-
(let [fib (fn fib [f-2 f-1 current] ; <label id="code.tail-fibo.args"/>
17-
(let [f (+ f-2 f-1)]
18-
(if (= n current) ; <label id="code.tail-fibo.term"/>
19-
f
20-
(fib f-1 f (inc current)))))] ; <label id="code.tail-fibo.recur"/>
21-
(cond
22-
(= n 0) 0
23-
(= n 1) 1
24-
:else (fib 0 1 2)))) ; <label id="code.tail-fibo.basis"/>
15+
(letfn [(fib ; <label id="code.tail-fibo.letfn"/>
16+
[current next n] ; <label id="code.tail-fibo.args"/>
17+
(if (zero? n)
18+
current ; <label id="code.tail-fibo.terminate"/>
19+
(fib next (+ current next) (dec n))))] ; <label id="code.tail-fibo.recur"/>
20+
(fib 0 1 n))) ; <label id="code.tail-fibo.call"/>
2521
; END: tail-fibo
2622

2723
; START: recur-fibo
2824
; better but not great
2925
(defn recur-fibo [n]
30-
(let [fib (fn [f-2 f-1 current]
31-
(let [f (+ f-2 f-1)]
32-
(if (= n current)
33-
f
34-
(recur f-1 f (inc current)))))] ; <label id="code.recur-fibo.recur"/>
35-
(cond
36-
(= n 0) 0
37-
(= n 1) 1
38-
:else (fib 0 1 2))))
26+
(letfn [(fib
27+
[current next n]
28+
(if (zero? n)
29+
current
30+
(recur next (+ current next) (dec n))))] ; <label id="code.recur-fibo.recur"/>
31+
(fib 0 1 n)))
3932
; END: recur-fibo
4033

41-
; START: fibo-series
42-
; returns series to n
43-
; still bad (heap-consuming!)
44-
(defn fibo-series [count]
45-
(let [n (dec count)
46-
fib (fn [series current] ; <label id="code.fibo-series.series"/>
47-
(let [f (+ (series (- current 1)) (series (- current 2)))]
48-
(if (= current n)
49-
(conj series f) ; <label id="code.fibo-series.term"/>
50-
(recur (conj series f) (inc current)))))] ; <label id="code.fibo-series.recur"/>
51-
(cond
52-
(= n 0) [0] ; <label id="code.fibo-series.0"/>
53-
(= n 1) [0 1] ; <label id="code.fibo-series.1"/>
54-
:else (fib [0 1] 2))))
55-
; END: fibo-series
56-
5734
; START: lazy-seq-fibo
5835
(defn lazy-seq-fibo
5936
([]
@@ -88,7 +65,7 @@
8865

8966
; START: by-pairs
9067
(defn by-pairs [coll]
91-
(let [take-pair (fn take-pair [c] ; <label id="code.by-pairs.take"/>
68+
(let [take-pair (fn [c] ; <label id="code.by-pairs.take"/>
9269
(when (next c) (take 2 c)))]
9370
(lazy-seq ; <label id="code.by-pairs.lazy-seq"/>
9471
(when-let [pair (seq (take-pair coll))] ; <label id="code.by-pairs.when-let"/>
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‎examples/male_female.clj‎

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+2-2Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -4,12 +4,12 @@
44
; do not use these directly
55
(declare m f)
66
(defn m [n]
7-
(if (= n 0)
7+
(if (zero? n)
88
0
99
(- n (f (m (dec n))))))
1010

1111
(defn f [n]
12-
(if (= n 0)
12+
(if (zero? n)
1313
1
1414
(- n (m (f (dec n))))))
1515
; END: m-f
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‎examples/male_female_seq.clj‎

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+2-2Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -3,12 +3,12 @@
33

44
(declare m f)
55
(defn- m [n]
6-
(if (= n 0)
6+
(if (zero? n)
77
0
88
(- n (f (m (dec n))))))
99

1010
(defn- f [n]
11-
(if (= n 0)
11+
(if (zero? n)
1212
1
1313
(- n (m (f (dec n))))))
1414

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‎examples/memoized_male_female.clj‎

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+2-2Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -4,12 +4,12 @@
44
; See http://en.wikipedia.org/wiki/Hofstadter_sequence
55
(declare m f)
66
(defn- m [n]
7-
(if (= n 0)
7+
(if (zero? n)
88
0
99
(- n (f (m (dec n))))))
1010

1111
(defn- f [n]
12-
(if (= n 0)
12+
(if (zero? n)
1313
1
1414
(- n (m (f (dec n))))))
1515

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‎examples/test/functional.clj‎

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-3Lines changed: 0 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -16,9 +16,6 @@
1616
(deftest test-recur-fibo
1717
(is (= ten-fibs (map recur-fibo (range 0 10)))))
1818

19-
(deftest test-fibo-series
20-
(is (= ten-fibs (fibo-series 10))))
21-
2219
(deftest test-fibo
2320
(is (= ten-fibs (take 10 (fibo)))))
2421

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