1 | [[tags: manual]] |
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2 | [[toc:]] |
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3 | |
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4 | == Unit data-structures |
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5 | |
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6 | This unit contains a collection of procedures related to data |
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7 | structures. |
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8 | |
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9 | |
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10 | === Lists |
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11 | |
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12 | |
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13 | ==== alist-ref |
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14 | |
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15 | [procedure] (alist-ref KEY ALIST [TEST [DEFAULT]]) |
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16 | |
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17 | Looks up {{KEY}} in {{ALIST}} using {{TEST}} as the comparison function (or {{eqv?}} if |
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18 | no test was given) and returns the cdr of the found pair, or {{DEFAULT}} (which defaults to {{#f}}). |
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19 | |
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20 | |
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21 | ==== alist-update! |
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22 | |
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23 | [procedure] (alist-update! KEY VALUE ALIST [TEST]) |
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24 | |
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25 | If the list {{ALIST}} contains a pair of the form {{(KEY . X)}}, then this procedure |
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26 | replaces {{X}} with {{VALUE}} and returns {{ALIST}}. If {{ALIST}} contains no such item, then |
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27 | {{alist-update!}} returns {{((KEY . VALUE) . ALIST)}}. The optional argument |
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28 | {{TEST}} specifies the comparison procedure to search a matching pair in {{ALIST}} |
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29 | and defaults to {{eqv?}}. |
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30 | |
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31 | |
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32 | ==== atom? |
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33 | |
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34 | [procedure] (atom? X) |
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35 | |
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36 | Returns {{#t}} if {{X}} is not a pair. This is identical to {{not-pair?}} from [[Unit srfi-1]] but |
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37 | kept for historical reasons. |
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38 | |
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39 | |
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40 | ==== rassoc |
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41 | |
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42 | [procedure] (rassoc KEY LIST [TEST]) |
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43 | |
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44 | Similar to {{assoc}}, but compares {{KEY}} with the {{cdr}} of each pair in {{LIST}} using |
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45 | {{TEST}} as the comparison procedures (which defaults to {{eqv?}}. |
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46 | |
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47 | |
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48 | ==== butlast |
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49 | |
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50 | [procedure] (butlast LIST) |
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51 | |
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52 | Returns a fresh list with all elements but the last of {{LIST}}. |
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53 | |
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54 | |
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55 | ==== chop |
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56 | |
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57 | [procedure] (chop LIST N) |
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58 | |
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59 | Returns a new list of sublists, where each sublist contains {{N}} |
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60 | elements of {{LIST}}. If {{LIST}} has a length that is not |
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61 | a multiple of {{N}}, then the last sublist contains the remaining |
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62 | elements. |
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63 | |
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64 | <enscript highlight=scheme> |
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65 | (chop '(1 2 3 4 5 6) 2) ==> ((1 2) (3 4) (5 6)) |
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66 | (chop '(a b c d) 3) ==> ((a b c) (d)) |
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67 | </enscript> |
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68 | |
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69 | |
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70 | ==== compress |
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71 | |
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72 | [procedure] (compress BLIST LIST) |
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73 | |
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74 | Returns a new list with elements taken from {{LIST}} with |
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75 | corresponding true values in the list {{BLIST}}. |
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76 | |
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77 | <enscript highlight=scheme> |
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78 | (define nums '(99 100 110 401 1234)) |
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79 | (compress (map odd? nums) nums) ==> (99 401) |
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80 | </enscript> |
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81 | |
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82 | |
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83 | ==== flatten |
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84 | |
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85 | [procedure] (flatten LIST1 ...) |
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86 | |
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87 | Returns {{LIST1 ...}} concatenated together, with nested lists |
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88 | removed (flattened). |
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89 | |
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90 | |
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91 | ==== intersperse |
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92 | |
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93 | [procedure] (intersperse LIST X) |
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94 | |
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95 | Returns a new list with {{X}} placed between each element. |
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96 | |
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97 | |
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98 | ==== join |
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99 | |
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100 | [procedure] (join LISTOFLISTS [LIST]) |
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101 | |
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102 | Concatenates the lists in {{LISTOFLISTS}} with {{LIST}} placed |
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103 | between each sublist. {{LIST}} defaults to the empty list. |
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104 | |
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105 | <enscript highlight=scheme> |
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106 | (join '((a b) (c d) (e)) '(x y)) ==> (a b x y c d x y e) |
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107 | (join '((p q) () (r (s) t)) '(-)) ==> (p q - - r (s) t) |
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108 | </enscript> |
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109 | |
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110 | {{join}} could be implemented as follows: |
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111 | |
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112 | <enscript highlight=scheme> |
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113 | (define (join lstoflsts #!optional (lst '())) |
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114 | (apply append (intersperse lstoflists lst)) ) |
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115 | </enscript> |
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116 | |
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117 | |
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118 | ==== shuffle |
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119 | |
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120 | [procedure] (shuffle LIST RANDOM) |
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121 | |
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122 | Returns {{LIST}} with its elements sorted in a random order given by |
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123 | procedure {{RANDOM}}. |
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124 | |
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125 | |
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126 | ==== tail? |
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127 | |
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128 | [procedure] (tail? X LIST) |
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129 | |
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130 | Returns true if {{X}} is one of the tails (cdr's) of {{LIST}}. |
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131 | |
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132 | === Queues |
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133 | |
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134 | |
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135 | ==== list->queue |
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136 | |
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137 | [procedure] (list->queue LIST) |
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138 | |
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139 | Returns {{LIST}} converted into a queue, where the first element |
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140 | of the list is the same as the first element of the queue. The resulting |
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141 | queue may share memory with the list and the list should not be modified |
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142 | after this operation. |
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143 | |
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144 | |
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145 | ==== make-queue |
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146 | |
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147 | [procedure] (make-queue) |
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148 | |
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149 | Returns a newly created queue. |
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150 | |
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151 | |
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152 | ==== queue? |
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153 | |
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154 | [procedure] (queue? X) |
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155 | |
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156 | Returns {{#t}} if {{X}} is a queue, or {{#f}} otherwise. |
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157 | |
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158 | |
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159 | ==== queue->list |
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160 | |
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161 | [procedure] (queue->list QUEUE) |
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162 | |
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163 | Returns {{QUEUE}} converted into a list, where the first element |
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164 | of the list is the same as the first element of the queue. The resulting |
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165 | list may share memory with the queue object and should not be modified. |
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166 | |
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167 | |
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168 | ==== queue-add! |
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169 | |
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170 | [procedure] (queue-add! QUEUE X) |
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171 | |
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172 | Adds {{X}} to the rear of {{QUEUE}}. |
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173 | |
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174 | |
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175 | ==== queue-empty? |
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176 | |
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177 | [procedure] (queue-empty? QUEUE) |
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178 | |
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179 | Returns {{#t}} if {{QUEUE}} is empty, or {{#f}} otherwise. |
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180 | |
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181 | |
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182 | ==== queue-first |
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183 | |
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184 | [procedure] (queue-first QUEUE) |
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185 | |
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186 | Returns the first element of {{QUEUE}}. If {{QUEUE}} is empty |
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187 | an error is signaled |
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188 | |
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189 | |
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190 | ==== queue-last |
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191 | |
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192 | [procedure] (queue-last QUEUE) |
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193 | |
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194 | Returns the last element of {{QUEUE}}. If {{QUEUE}} is empty |
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195 | an error is signaled |
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196 | |
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197 | |
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198 | ==== queue-remove! |
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199 | |
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200 | [procedure] (queue-remove! QUEUE) |
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201 | |
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202 | Removes and returns the first element of {{QUEUE}}. If {{QUEUE}} |
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203 | is empty an error is signaled |
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204 | |
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205 | |
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206 | ==== queue-push-back! |
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207 | |
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208 | [procedure] (queue-push-back! QUEUE ITEM) |
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209 | |
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210 | Pushes an item into the first position of a queue, i.e. the next |
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211 | {{queue-remove!}} will return {{ITEM}}. |
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212 | |
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213 | |
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214 | ==== queue-push-back-list! |
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215 | |
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216 | [procedure] (queue-push-back-list! QUEUE LIST) |
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217 | |
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218 | Pushes the items in item-list back onto the queue, |
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219 | so that {{(car LIST)}} becomes the next removable item. |
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220 | |
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221 | |
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222 | |
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223 | === Sorting |
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224 | |
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225 | |
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226 | ==== merge |
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227 | |
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228 | [procedure] (merge LIST1 LIST2 LESS?) |
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229 | [procedure] (merge! LIST1 LIST2 LESS?) |
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230 | |
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231 | Joins two lists in sorted order. {{merge!}} is the destructive |
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232 | version of merge. {{LESS? }} should be a procedure of two arguments, |
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233 | that returns true if the first argument is to be ordered before the |
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234 | second argument. |
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235 | |
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236 | |
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237 | ==== sort |
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238 | |
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239 | [procedure] (sort SEQUENCE LESS?) |
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240 | [procedure] (sort! SEQUENCE LESS?) |
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241 | |
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242 | Sort {{SEQUENCE}}, which should be a list or a vector. {{sort!}} |
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243 | is the destructive version of sort. |
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244 | |
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245 | |
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246 | ==== sorted? |
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247 | |
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248 | [procedure] (sorted? SEQUENCE LESS?) |
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249 | |
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250 | Returns true if the list or vector {{SEQUENCE}} is already sorted. |
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251 | |
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252 | |
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253 | ==== topological-sort |
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254 | |
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255 | [procedure] (topological-sort DAG PRED) |
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256 | |
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257 | Sorts the directed acyclic graph dag {{DAG}} so that for every edge from vertex |
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258 | u to v, u will come before v in the resulting list of vertices. |
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259 | |
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260 | {{DAG}} is a list of sublists. The car of each sublist is a |
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261 | vertex. The cdr is the adjacency list of that vertex, i.e. a list of |
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262 | all vertices to which there exists an edge from the car vertex. |
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263 | {{pred}} is procedure of two arguments that should compare vertices |
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264 | for equality. |
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265 | |
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266 | Time complexity: O (|V| + |E|) |
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267 | |
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268 | <enscript highlight=scheme> |
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269 | (require 'tsort) |
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270 | (topological-sort |
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271 | '((shirt tie belt) |
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272 | (tie jacket) |
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273 | (belt jacket) |
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274 | (watch) |
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275 | (pants shoes belt) |
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276 | (undershorts pants shoes) |
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277 | (socks shoes)) |
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278 | eq?) |
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279 | |
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280 | => |
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281 | |
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282 | (socks undershorts pants shoes watch shirt belt tie jacket) |
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283 | </enscript> |
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284 | |
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285 | |
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286 | === Random numbers |
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287 | |
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288 | |
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289 | ==== random-seed |
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290 | |
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291 | [procedure] (random-seed [SEED]) |
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292 | |
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293 | Seeds the random number generator with {{SEED}} (an exact integer) or |
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294 | {{(current-seconds)}} if {{SEED}} is not given. |
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295 | |
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296 | |
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297 | === Strings |
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298 | |
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299 | |
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300 | ==== conc |
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301 | |
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302 | [procedure] (conc X ...) |
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303 | |
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304 | Returns a string with the string-represenation of all arguments concatenated |
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305 | together. {{conc}} could be implemented as |
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306 | |
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307 | <enscript highlight=scheme> |
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308 | (define (conc . args) |
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309 | (apply string-append (map ->string args)) ) |
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310 | </enscript> |
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311 | |
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312 | |
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313 | |
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314 | ==== ->string |
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315 | |
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316 | [procedure] (->string X) |
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317 | |
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318 | Returns a string-representation of {{X}}. |
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319 | |
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320 | |
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321 | ==== string-chop |
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322 | |
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323 | [procedure] (string-chop STRING LENGTH) |
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324 | |
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325 | Returns a list of substrings taken by ''chopping'' {{STRING}} every {{LENGTH}} |
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326 | characters: |
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327 | |
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328 | <enscript highlight=scheme> |
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329 | (string-chop "one two three" 4) ==> ("one " "two " "thre" "e") |
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330 | </enscript> |
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331 | |
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332 | |
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333 | |
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334 | ==== string-chomp |
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335 | |
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336 | [procedure] (string-chomp STRING [SUFFIX]) |
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337 | |
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338 | If {{STRING}} ends with {{SUFFIX}}, then this procedure returns a copy of its first argument with the suffix |
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339 | removed, otherwise returns {{STRING}} unchanged. {{SUFFIX}} defaults to {{"\n"}}. |
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340 | |
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341 | |
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342 | ==== string-compare3 |
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343 | |
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344 | [procedure] (string-compare3 STRING1 STRING2) |
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345 | [procedure] (string-compare3-ci STRING1 STRING2) |
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346 | |
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347 | Perform a three-way comparison between the {{STRING1}} and {{STRING2}}, |
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348 | returning either {{-1}} if {{STRING1}} is lexicographically less |
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349 | than {{STRING2}}, {{0}} if it is equal, or {{1}} if it s greater. |
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350 | {{string-compare3-ci}} performs a case-insensitive comparison. |
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351 | |
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352 | |
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353 | ==== string-intersperse |
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354 | |
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355 | [procedure] (string-intersperse LIST [STRING]) |
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356 | |
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357 | Returns a string that contains all strings in {{LIST}} concatenated |
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358 | together. {{STRING}} is placed between each concatenated string and |
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359 | defaults to {{" "}}. |
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360 | |
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361 | <enscript highlight=scheme> |
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362 | (string-intersperse '("one" "two") "three") |
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363 | </enscript> |
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364 | |
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365 | is equivalent to |
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366 | |
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367 | <enscript highlight=scheme> |
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368 | (apply string-append (intersperse '("one" "two") "three")) |
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369 | </enscript> |
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370 | |
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371 | |
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372 | ==== string-split |
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373 | |
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374 | [procedure] (string-split STRING [DELIMITER-STRING [KEEPEMPTY]]) |
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375 | |
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376 | Split string into substrings separated by the given delimiters. If |
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377 | no delimiters are specified, a string comprising the tab, newline and space characters |
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378 | is assumed. If the |
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379 | parameter {{KEEPEMPTY}} is given and not {{#f}}, then empty |
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380 | substrings are retained: |
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381 | |
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382 | <enscript highlight=scheme> |
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383 | (string-split "one two three") ==> ("one" "two" "three") |
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384 | (string-split "foo:bar::baz:" ":" #t) ==> ("foo" "bar" "" "baz" "") |
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385 | </enscript> |
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386 | |
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387 | |
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388 | ==== string-translate |
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389 | |
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390 | [procedure] (string-translate STRING FROM [TO]) |
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391 | |
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392 | Returns a fresh copy of {{STRING}} with characters matching |
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393 | {{FROM}} translated to {{TO}}. If {{TO}} is omitted, then |
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394 | matching characters are removed. {{FROM}} and {{TO}} may be |
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395 | a character, a string or a list. If both {{FROM}} and {{TO}} |
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396 | are strings, then the character at the same position in {{TO}} |
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397 | as the matching character in {{FROM}} is substituted. |
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398 | |
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399 | |
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400 | ==== string-translate* |
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401 | |
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402 | [procedure] (string-translate* STRING SMAP) |
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403 | |
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404 | Substitutes elements of {{STRING}} according to {{SMAP}}. |
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405 | {{SMAP}} should be an association-list where each element of the list |
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406 | is a pair of the form {{(MATCH \. REPLACEMENT)}}. Every occurrence of |
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407 | the string {{MATCH}} in {{STRING}} will be replaced by the string |
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408 | {{REPLACEMENT}}: |
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409 | |
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410 | <enscript highlight=scheme> |
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411 | (string-translate* |
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412 | "<h1>this is a \"string\"</h1>" |
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413 | '(("<" . "<") (">" . ">") ("\"" . """)) ) |
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414 | => "<h1>this is a "string"</h1>" |
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415 | </enscript> |
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416 | |
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417 | |
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418 | ==== substring=? |
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419 | |
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420 | [procedure] (substring=? STRING1 STRING2 [START1 [START2 [LENGTH]]]) |
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421 | [procedure] (substring-ci=? STRING1 STRING2 [START1 [START2 [LENGTH]]]) |
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422 | |
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423 | Returns {{#t}} if the strings {{STRING1}} and {{STRING2}} are equal, or |
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424 | {{#f}} otherwise. |
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425 | The comparison starts at the positions {{START1}} and {{START2}} (which default |
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426 | to 0), comparing {{LENGTH}} characters (which defaults to the minimum of the remaining |
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427 | length of both strings). |
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428 | |
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429 | |
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430 | ==== substring-index |
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431 | |
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432 | [procedure] (substring-index WHICH WHERE [START]) |
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433 | [procedure] (substring-index-ci WHICH WHERE [START]) |
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434 | |
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435 | Searches for first index in string {{WHERE}} where string |
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436 | {{WHICH}} occurs. If the optional argument {{START}} is given, |
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437 | then the search starts at that index. {{substring-index-ci}} |
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438 | is a case-insensitive version of {{substring-index}}. |
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439 | |
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440 | |
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441 | |
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442 | === Combinators |
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443 | |
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444 | |
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445 | ==== any? |
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446 | |
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447 | [procedure] (any? X) |
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448 | |
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449 | Ignores its argument and always returns {{#t}}. This is actually useful sometimes. |
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450 | |
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451 | |
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452 | ==== none? |
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453 | |
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454 | [procedure] (none? X) |
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455 | |
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456 | Ignores its argument and always returns {{#f}}. This is actually useful sometimes. |
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457 | |
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458 | |
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459 | ==== always? |
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460 | |
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461 | [procedure] (always? X) |
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462 | |
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463 | Ignores its arguments and always returns {{#t}}. This is actually useful sometimes. |
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464 | |
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465 | |
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466 | ==== never? |
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467 | |
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468 | [procedure] (never? X) |
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469 | |
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470 | Ignores its arguments and always returns {{#f}}. This is actually useful sometimes. |
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471 | |
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472 | |
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473 | ==== constantly |
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474 | |
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475 | [procedure] (constantly X ...) |
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476 | |
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477 | Returns a procedure that always returns the values {{X ...}} regardless of the number and value of its arguments. |
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478 | |
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479 | <enscript highlight=scheme> |
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480 | (constantly X) <=> (lambda args X) |
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481 | </enscript> |
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482 | |
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483 | |
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484 | ==== complement |
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485 | |
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486 | [procedure] (complement PROC) |
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487 | |
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488 | Returns a procedure that returns the boolean inverse of {{PROC}}. |
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489 | |
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490 | <enscript highlight=scheme> |
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491 | (complement PROC) <=> (lambda (x) (not (PROC x))) |
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492 | </enscript> |
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493 | |
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494 | |
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495 | ==== compose |
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496 | |
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497 | [procedure] (compose PROC1 PROC2 ...) |
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498 | |
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499 | Returns a procedure that represents the composition of the |
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500 | argument-procedures {{PROC1 PROC2 ...}}. |
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501 | |
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502 | <enscript highlight=scheme> |
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503 | (compose F G) <=> (lambda args |
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504 | (call-with-values |
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505 | (lambda () (apply G args)) |
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506 | F)) |
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507 | </enscript> |
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508 | |
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509 | {{(compose)}} is equivalent to {{values}}. |
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510 | |
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511 | |
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512 | ==== conjoin |
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513 | |
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514 | [procedure] (conjoin PRED ...) |
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515 | |
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516 | Returns a procedure that returns {{#t}} if its argument satisfies the |
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517 | predicates {{PRED ...}}. |
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518 | <enscript highlight=scheme> |
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519 | ((conjoin odd? positive?) 33) ==> #t |
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520 | ((conjoin odd? positive?) -33) ==> #f |
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521 | </enscript> |
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522 | |
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523 | |
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524 | ==== disjoin |
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525 | |
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526 | [procedure] (disjoin PRED ...) |
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527 | |
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528 | Returns a procedure that returns {{#t}} if its argument satisfies any |
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529 | predicate {{PRED ...}}. |
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530 | <enscript highlight=scheme> |
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531 | ((disjoin odd? positive?) 32) ==> #t |
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532 | ((disjoin odd? positive?) -32) ==> #f |
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533 | </enscript> |
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534 | |
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535 | |
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536 | ==== each |
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537 | |
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538 | [procedure] (each PROC ...) |
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539 | |
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540 | Returns a procedure that applies {{PROC ...}} to its arguments, and returns the result(s) |
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541 | of the last procedure application. For example |
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542 | |
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543 | <enscript highlight=scheme> |
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544 | (each pp eval) |
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545 | </enscript> |
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546 | |
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547 | is equivalent to |
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548 | |
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549 | <enscript highlight=scheme> |
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550 | (lambda args |
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551 | (apply pp args) |
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552 | (apply eval args) ) |
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553 | </enscript> |
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554 | |
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555 | {{(each PROC)}} is equivalent to {{PROC}} and {{(each)}} is equivalent to |
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556 | {{noop}}. |
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557 | |
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558 | |
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559 | ==== flip |
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560 | |
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561 | [procedure] (flip PROC) |
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562 | |
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563 | Returns a two-argument procedure that calls {{PROC}} with its |
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564 | arguments swapped: |
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565 | <enscript highlight=scheme> |
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566 | (flip PROC) <=> (lambda (x y) (PROC y x)) |
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567 | </enscript> |
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568 | |
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569 | |
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570 | ==== identity |
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571 | |
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572 | [procedure] (identity X) |
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573 | |
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574 | Returns its sole argument {{X}}. |
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575 | |
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576 | |
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577 | ==== project |
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578 | |
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579 | [procedure] (project N) |
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580 | |
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581 | Returns a procedure that returns its {{N}}th argument (starting from 0). |
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582 | |
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583 | |
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584 | ==== list-of? |
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585 | |
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586 | [procedure] (list-of? PRED) |
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587 | |
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588 | Returns a procedure of one argument that returns {{#t}} when |
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589 | applied to a list of elements that all satisfy the predicate procedure |
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590 | {{PRED}}, or {{#f}} otherwise. |
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591 | |
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592 | <enscript highlight=scheme> |
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593 | ((list-of? even?) '(1 2 3)) ==> #f |
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594 | ((list-of? number?) '(1 2 3)) ==> #t |
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595 | </enscript> |
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596 | |
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597 | |
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598 | ==== noop |
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599 | |
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600 | [procedure] (noop X ...) |
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601 | |
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602 | Ignores it's arguments, does nothing and returns an unspecified value. |
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603 | |
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604 | |
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605 | ==== o |
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606 | |
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607 | [procedure] (o PROC ...) |
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608 | |
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609 | A single value version of {{compose}} (slightly faster). {{(o)}} is equivalent |
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610 | to {{identity}}. |
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611 | |
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612 | |
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613 | ==== left-section |
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614 | |
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615 | [procedure] (left-section PROC ARG0 ...) |
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616 | |
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617 | Returns a procedure that partially applies some of its' arguments starting from the left. |
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618 | |
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619 | {{PROC}} a procedure. |
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620 | |
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621 | {{ARG0 ...}} some prefix of the arguments for {{PROC}}. |
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622 | |
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623 | |
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624 | ==== right-section |
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625 | |
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626 | [procedure] (right-section PROC ARG0 ...) |
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627 | |
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628 | Returns a procedure that partially applies some of its' arguments starting from the right. |
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629 | |
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630 | {{PROC}} a procedure. |
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631 | |
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632 | {{ARG0 ...}} some reversed suffix of the arguments for {{PROC}}. |
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633 | |
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634 | |
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635 | |
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636 | === Binary searching |
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637 | |
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638 | |
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639 | ==== binary-search |
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640 | |
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641 | [procedure] (binary-search SEQUENCE PROC) |
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642 | |
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643 | Performs a binary search in {{SEQUENCE}}, which should be a sorted |
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644 | list or vector. {{PROC}} is called to compare items in the sequence, |
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645 | should accept a single argument and return an exact integer: zero if the |
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646 | searched value is equal to the current item, negative if the searched |
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647 | value is ''less'' than the current item, and positive otherwise. |
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648 | Returns the index of the found value or {{#f}} otherwise. |
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649 | |
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650 | --- |
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651 | Previous: [[Unit expand]] |
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652 | |
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653 | Next: [[Unit ports]] |
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