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1 ; Copyright (c) Rich Hickey. All rights reserved.
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2 ; The use and distribution terms for this software are covered by the
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3 ; Eclipse Public License 1.0 (http://opensource.org/licenses/eclipse-1.0.php)
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4 ; which can be found in the file epl-v10.html at the root of this distribution.
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5 ; By using this software in any fashion, you are agreeing to be bound by
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6 ; the terms of this license.
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7 ; You must not remove this notice, or any other, from this software.
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8
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rlm@10
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9 ;;; walk.clj - generic tree walker with replacement
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10
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11 ;; by Stuart Sierra
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12 ;; December 15, 2008
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13
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14 ;; CHANGE LOG:
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15 ;;
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16 ;; * December 15, 2008: replaced 'walk' with 'prewalk' & 'postwalk'
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17 ;;
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18 ;; * December 9, 2008: first version
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19
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20
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21 (ns
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22 ^{:author "Stuart Sierra",
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23 :doc "This file defines a generic tree walker for Clojure data
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24 structures. It takes any data structure (list, vector, map, set,
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25 seq), calls a function on every element, and uses the return value
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26 of the function in place of the original. This makes it fairly
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27 easy to write recursive search-and-replace functions, as shown in
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28 the examples.
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29
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30 Note: \"walk\" supports all Clojure data structures EXCEPT maps
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31 created with sorted-map-by. There is no (obvious) way to retrieve
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32 the sorting function."}
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33 clojure.walk)
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34
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35 (defn walk
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36 "Traverses form, an arbitrary data structure. inner and outer are
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37 functions. Applies inner to each element of form, building up a
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38 data structure of the same type, then applies outer to the result.
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39 Recognizes all Clojure data structures except sorted-map-by.
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40 Consumes seqs as with doall."
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41 {:added "1.1"}
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42 [inner outer form]
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43 (cond
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44 (list? form) (outer (apply list (map inner form)))
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45 (seq? form) (outer (doall (map inner form)))
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46 (vector? form) (outer (vec (map inner form)))
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47 (map? form) (outer (into (if (sorted? form) (sorted-map) {})
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48 (map inner form)))
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49 (set? form) (outer (into (if (sorted? form) (sorted-set) #{})
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50 (map inner form)))
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51 :else (outer form)))
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52
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53 (defn postwalk
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54 "Performs a depth-first, post-order traversal of form. Calls f on
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55 each sub-form, uses f's return value in place of the original.
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56 Recognizes all Clojure data structures except sorted-map-by.
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57 Consumes seqs as with doall."
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58 {:added "1.1"}
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59 [f form]
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60 (walk (partial postwalk f) f form))
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61
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62 (defn prewalk
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63 "Like postwalk, but does pre-order traversal."
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64 {:added "1.1"}
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65 [f form]
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66 (walk (partial prewalk f) identity (f form)))
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67
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68
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69 ;; Note: I wanted to write:
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70 ;;
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71 ;; (defn walk
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72 ;; [f form]
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73 ;; (let [pf (partial walk f)]
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74 ;; (if (coll? form)
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75 ;; (f (into (empty form) (map pf form)))
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76 ;; (f form))))
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77 ;;
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78 ;; but this throws a ClassCastException when applied to a map.
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79
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80
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81 (defn postwalk-demo
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82 "Demonstrates the behavior of postwalk by printing each form as it is
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83 walked. Returns form."
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84 {:added "1.1"}
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85 [form]
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86 (postwalk (fn [x] (print "Walked: ") (prn x) x) form))
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87
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88 (defn prewalk-demo
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89 "Demonstrates the behavior of prewalk by printing each form as it is
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90 walked. Returns form."
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91 {:added "1.1"}
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92 [form]
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93 (prewalk (fn [x] (print "Walked: ") (prn x) x) form))
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94
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95 (defn keywordize-keys
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96 "Recursively transforms all map keys from strings to keywords."
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97 {:added "1.1"}
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98 [m]
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99 (let [f (fn [[k v]] (if (string? k) [(keyword k) v] [k v]))]
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100 ;; only apply to maps
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101 (postwalk (fn [x] (if (map? x) (into {} (map f x)) x)) m)))
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102
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103 (defn stringify-keys
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104 "Recursively transforms all map keys from keywords to strings."
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105 {:added "1.1"}
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106 [m]
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107 (let [f (fn [[k v]] (if (keyword? k) [(name k) v] [k v]))]
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108 ;; only apply to maps
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109 (postwalk (fn [x] (if (map? x) (into {} (map f x)) x)) m)))
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110
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111 (defn prewalk-replace
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112 "Recursively transforms form by replacing keys in smap with their
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113 values. Like clojure/replace but works on any data structure. Does
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114 replacement at the root of the tree first."
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115 {:added "1.1"}
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116 [smap form]
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117 (prewalk (fn [x] (if (contains? smap x) (smap x) x)) form))
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118
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119 (defn postwalk-replace
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120 "Recursively transforms form by replacing keys in smap with their
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121 values. Like clojure/replace but works on any data structure. Does
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122 replacement at the leaves of the tree first."
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123 {:added "1.1"}
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124 [smap form]
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125 (postwalk (fn [x] (if (contains? smap x) (smap x) x)) form))
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126
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127 (defn macroexpand-all
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128 "Recursively performs all possible macroexpansions in form."
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129 {:added "1.1"}
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130 [form]
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131 (prewalk (fn [x] (if (seq? x) (macroexpand x) x)) form))
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132
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