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1 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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2 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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3 ;;
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4 ;; Stream application examples
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5 ;;
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6 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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7 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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8
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9 (ns
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10 #^{:author "Konrad Hinsen"
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11 :skip-wiki true
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12 :doc "Examples for data streams"}
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13 clojure.contrib.stream-utils.examples
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14 (:refer-clojure :exclude (deftype))
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15 (:use [clojure.contrib.stream-utils
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16 :only (defst stream-next
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17 pick pick-all
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18 stream-type defstream
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19 stream-drop stream-map stream-filter stream-flatten)])
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20 (:use [clojure.contrib.monads :only (domonad)])
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21 (:use [clojure.contrib.types :only (deftype)])
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22 (:require [clojure.contrib.generic.collection :as gc]))
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23
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24 ;
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25 ; Define a stream of Fibonacci numbers
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26 ;
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27 (deftype ::fib-stream last-two-fib)
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28
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29 (defstream ::fib-stream
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30 [fs]
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31 (let [[n1 n2] fs]
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32 [n1 (last-two-fib [n2 (+ n1 n2)])]))
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33
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34 (def fib-stream (last-two-fib [0 1]))
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35
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36 (take 10 (gc/seq fib-stream))
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37
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38 ;
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39 ; A simple random number generator, implemented as a stream
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40 ;
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41 (deftype ::random-seed rng-seed vector seq)
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42
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43 (defstream ::random-seed
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44 [seed]
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45 (let [[seed] seed
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46 m 259200
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47 value (/ (float seed) (float m))
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48 next (rem (+ 54773 (* 7141 seed)) m)]
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49 [value (rng-seed next)]))
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50
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51 (take 10 (gc/seq (rng-seed 1)))
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52
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53 ;
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54 ; Various stream utilities
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55 ;
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56 (take 10 (gc/seq (stream-drop 10 (rng-seed 1))))
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57 (gc/seq (stream-map inc (range 5)))
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58 (gc/seq (stream-filter odd? (range 10)))
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59 (gc/seq (stream-flatten (partition 3 (range 9))))
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60
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61 ;
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62 ; Stream transformers
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63 ;
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64
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65 ; Transform a stream of numbers into a stream of sums of two
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66 ; consecutive numbers.
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67 (defst sum-two [] [xs]
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68 (domonad
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69 [x1 (pick xs)
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70 x2 (pick xs)]
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71 (+ x1 x2)))
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72
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73 (def s (sum-two '(1 2 3 4 5 6 7 8)))
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74
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75 (let [[v1 s] (stream-next s)]
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76 (let [[v2 s] (stream-next s)]
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77 (let [[v3 s] (stream-next s)]
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78 (let [[v4 s] (stream-next s)]
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79 (let [[v5 s] (stream-next s)]
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80 [v1 v2 v3 v4 v5])))))
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81
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82 (gc/seq s)
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83
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84 ; Map (for a single stream) written as a stream transformer
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85 (defst my-map-1 [f] [xs]
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86 (domonad
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87 [x (pick xs)]
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88 (f x)))
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89
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90 (gc/seq (my-map-1 inc [1 2 3]))
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91
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92 ; Map for two stream arguments
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93 (defst my-map-2 [f] [xs ys]
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94 (domonad
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95 [x (pick xs)
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96 y (pick ys)]
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97 (f x y)))
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98
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99 (gc/seq (my-map-2 + '(1 2 3 4) '(10 20 30 40)))
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100
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101 ; Map for any number of stream arguments
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102 (defst my-map [f] [& streams]
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103 (domonad
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104 [vs pick-all]
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105 (apply f vs)))
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106
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107 (gc/seq (my-map inc [1 2 3]))
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108 (gc/seq (my-map + '(1 2 3 4) '(10 20 30 40)))
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109
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110 ; Filter written as a stream transformer
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111 (defst my-filter [p] [xs]
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112 (domonad
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113 [x (pick xs) :when (p x)]
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114 x))
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115
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116 (gc/seq (my-filter odd? [1 2 3]))
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117
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