| 1 | { |
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| 2 | "demo1":[ |
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| 3 | { "type":"text", |
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| 4 | "value":"Consider two strings s1 and s1a that are in an aliasing relationship, and a third, s2, made by a simple copy from s1." |
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| 5 | }, |
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| 6 | { "type":"demo", |
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| 7 | "vars":["s1", "s1a", "s2"], |
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| 8 | "steps":[ |
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| 9 | { "code":["string s1 = \"abc\";", |
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| 10 | "string s1a = s1`shareEdits;", |
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| 11 | "string s2 = s1;"], |
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| 12 | "endvals":{ |
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| 13 | "s1":"abc", |
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| 14 | "s1a":"abc", |
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| 15 | "s2":"abc" |
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| 16 | } |
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| 17 | } |
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| 18 | ] |
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| 19 | }, |
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| 20 | { "type":"text", |
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| 21 | "value":"Aliasing (@`shareEdits@) means that changes flow in both directions; with a simple copy, they do not." |
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| 22 | }, |
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| 23 | { "type":"demo", |
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| 24 | "vars":["s1", "s1a", "s2"], |
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| 25 | "steps":[ |
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| 26 | { "endvals":{ |
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| 27 | "s1":"abc", |
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| 28 | "s1a":"abc", |
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| 29 | "s2":"abc" |
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| 30 | } |
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| 31 | }, |
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| 32 | { "code":["s1 [1] = '+';"], |
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| 33 | "endvals":{ |
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| 34 | "s1":"a+c", |
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| 35 | "s1a":"a+c", |
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| 36 | "s2":"abc" |
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| 37 | } |
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| 38 | }, |
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| 39 | { "code":["s1a[1] = '-';"], |
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| 40 | "endvals":{ |
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| 41 | "s1":"a-c", |
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| 42 | "s1a":"a-c", |
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| 43 | "s2":"abc" |
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| 44 | } |
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| 45 | }, |
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| 46 | { "code":["s2 [1] = '|';"], |
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| 47 | "endvals":{ |
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| 48 | "s1":"a-c", |
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| 49 | "s1a":"a-c", |
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| 50 | "s2":"a|c" |
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| 51 | } |
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| 52 | } |
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| 53 | ] |
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| 54 | }, |
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| 55 | { "type":"text", |
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| 56 | "value":"Assignment of a value is just a modificiation. The aliasing relationship is established at construction and is unaffected by assignment of a value." |
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| 57 | }, |
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| 58 | { "type":"demo", |
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| 59 | "vars":["s1", "s1a", "s2"], |
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| 60 | "steps":[ |
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| 61 | { "endvals":{ |
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| 62 | "s1":"a-c", |
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| 63 | "s1a":"a-c", |
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| 64 | "s2":"a|c" |
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| 65 | } |
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| 66 | }, |
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| 67 | { "code":["s1 = \"qrs\";"], |
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| 68 | "endvals":{ |
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| 69 | "s1":"qrs", |
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| 70 | "s1a":"qrs", |
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| 71 | "s2":"a|c" |
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| 72 | } |
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| 73 | }, |
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| 74 | { "code":["s1a = \"tuv\";"], |
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| 75 | "endvals":{ |
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| 76 | "s1":"tuv", |
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| 77 | "s1a":"tuv", |
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| 78 | "s2":"a|c" |
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| 79 | } |
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| 80 | }, |
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| 81 | { "code":["s2 = \"wxy\";"], |
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| 82 | "endvals":{ |
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| 83 | "s1":"tuv", |
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| 84 | "s1a":"tuv", |
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| 85 | "s2":"wxy" |
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| 86 | } |
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| 87 | } |
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| 88 | ] |
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| 89 | }, |
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| 90 | { "type":"text", |
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| 91 | "value":"Assignment from a string is just assignment of a value. RHS participaing in aliasing (or not) is irrelevant. Aliasing of LHS is unaffected." |
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| 92 | }, |
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| 93 | { "type":"demo", |
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| 94 | "vars":["s1", "s1a", "s2"], |
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| 95 | "steps":[ |
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| 96 | { "endvals":{ |
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| 97 | "s1":"tuv", |
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| 98 | "s1a":"tuv", |
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| 99 | "s2":"wxy" |
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| 100 | } |
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| 101 | }, |
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| 102 | { "code":["s1 = s2;"], |
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| 103 | "endvals":{ |
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| 104 | "s1":"wxy", |
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| 105 | "s1a":"wxy", |
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| 106 | "s2":"wxy" |
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| 107 | } |
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| 108 | }, |
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| 109 | { "code":["s1 = \"aaa\";"], |
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| 110 | "endvals":{ |
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| 111 | "s1":"aaa", |
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| 112 | "s1a":"aaa", |
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| 113 | "s2":"wxy" |
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| 114 | } |
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| 115 | }, |
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| 116 | { "code":["s2 = s1;"], |
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| 117 | "endvals":{ |
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| 118 | "s1":"aaa", |
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| 119 | "s1a":"aaa", |
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| 120 | "s2":"aaa" |
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| 121 | } |
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| 122 | }, |
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| 123 | { "code":["s2 = \"bbb\";"], |
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| 124 | "endvals":{ |
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| 125 | "s1":"aaa", |
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| 126 | "s1a":"aaa", |
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| 127 | "s2":"bbb" |
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| 128 | } |
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| 129 | }, |
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| 130 | { "code":["s2 = s1a;"], |
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| 131 | "endvals":{ |
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| 132 | "s1":"aaa", |
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| 133 | "s1a":"aaa", |
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| 134 | "s2":"aaa" |
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| 135 | } |
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| 136 | }, |
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| 137 | { "code":["s2 = \"ccc\";"], |
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| 138 | "endvals":{ |
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| 139 | "s1":"aaa", |
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| 140 | "s1a":"aaa", |
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| 141 | "s2":"ccc" |
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| 142 | } |
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| 143 | }, |
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| 144 | { "code":["s1 = \"xxx\";"], |
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| 145 | "endvals":{ |
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| 146 | "s1":"xxx", |
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| 147 | "s1a":"xxx", |
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| 148 | "s2":"ccc" |
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| 149 | } |
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| 150 | } |
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| 151 | ] |
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| 152 | } |
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| 153 | ], |
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| 154 | "demo2":[ |
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| 155 | { "type":"text", |
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| 156 | "value":"Consider new strings @s1_mid@ being an alias for a run in the middle of @s1@, along with @s2@, made by a simple copy from the middle of @s1@." |
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| 157 | }, |
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| 158 | { "type":"demo", |
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| 159 | "vars":["s1", "s1_mid", "s2"], |
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| 160 | "steps":[ |
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| 161 | { "code":["string s1 = \"abcd\";", |
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| 162 | "string s1_mid = s1(1,3)`shareEdits;", |
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| 163 | "string s2 = s1(1,3);"], |
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| 164 | "endvals":{ |
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| 165 | "s1":"abcd", |
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| 166 | "s1_mid":"bc", |
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| 167 | "s2":"bc" |
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| 168 | } |
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| 169 | } |
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| 170 | ] |
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| 171 | }, |
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| 172 | { "type":"text", |
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| 173 | "value":"Again, @`shareEdits@ passes changes in both directions; copy does not. Note the difference in index values, with the \\emph{b} position being 1 in the longer string and 0 in the shorter strings. In the case of s1 aliasing with @s1_mid@, the very same character is being accessed by different postitions." |
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| 174 | }, |
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| 175 | { "type":"demo", |
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| 176 | "vars":["s1", "s1_mid", "s2"], |
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| 177 | "steps":[ |
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| 178 | { "endvals":{ |
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| 179 | "s1":"abcd", |
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| 180 | "s1_mid":"bc", |
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| 181 | "s2":"bc" |
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| 182 | } |
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| 183 | }, |
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| 184 | { "code":["s1 [1] = '+';"], |
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| 185 | "endvals":{ |
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| 186 | "s1":"a+cd", |
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| 187 | "s1_mid":"+c", |
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| 188 | "s2":"bc" |
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| 189 | } |
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| 190 | }, |
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| 191 | { "code":["s1_mid[0] = '-';"], |
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| 192 | "endvals":{ |
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| 193 | "s1":"a-cd", |
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| 194 | "s1_mid":"-c", |
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| 195 | "s2":"bc" |
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| 196 | } |
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| 197 | }, |
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| 198 | { "code":["s2 [0] = '|';"], |
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| 199 | "endvals":{ |
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| 200 | "s1":"a-cd", |
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| 201 | "s1_mid":"-c", |
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| 202 | "s2":"|c" |
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| 203 | } |
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| 204 | } |
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| 205 | ] |
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| 206 | }, |
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| 207 | { "type":"text", |
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| 208 | "value":"Once again, assignment of a value is a modificiation that flows through the aliasing relationship, without affecting its structure." |
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| 209 | }, |
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| 210 | { "type":"demo", |
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| 211 | "vars":["s1", "s1_mid", "s2"], |
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| 212 | "steps":[ |
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| 213 | { "endvals":{ |
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| 214 | "s1":"a-cd", |
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| 215 | "s1_mid":"-c", |
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| 216 | "s2":"|c" |
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| 217 | } |
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| 218 | }, |
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| 219 | { "code":["s1_mid = \"ff\";"], |
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| 220 | "endvals":{ |
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| 221 | "s1":"affd", |
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| 222 | "s1_mid":"ff", |
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| 223 | "s2":"|c" |
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| 224 | } |
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| 225 | }, |
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| 226 | { "code":["s2 = \"gg\";"], |
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| 227 | "endvals":{ |
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| 228 | "s1":"affd", |
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| 229 | "s1_mid":"ff", |
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| 230 | "s2":"gg" |
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| 231 | } |
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| 232 | } |
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| 233 | ] |
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| 234 | }, |
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| 235 | { "type":"text", |
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| 236 | "value":"In the \\emph{ff} step, which is a positive example of flow across an aliasing relationship, the result is straightforward to accept because the flow direction is from contained (small) to containing (large). The following rules for edits through aliasing substrings will guide how to flow in the opposite direction.\n\n" |
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| 237 | }, |
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| 238 | { "type":"text", |
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| 239 | "value":"Growth and shrinkage are natural extensions. An empty substring is a real thing, at a well-defined location, whose meaning is extrapolated from the examples so far. The intended metaphor is to operating a GUI text editor. Having an aliasing substring is like using the mouse to select a few words. Assigning onto an aliasign substring is like typing from having a few words selected: depending how much you type, the file being edited can get shorter or longer." |
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| 240 | }, |
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| 241 | { "type":"demo", |
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| 242 | "vars":["s1", "s1_mid"], |
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| 243 | "steps":[ |
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| 244 | { "endvals":{ |
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| 245 | "s1":"affd", |
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| 246 | "s1_mid":"fc" |
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| 247 | } |
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| 248 | }, |
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| 249 | { "code":["s1_mid = \"hhhh\";"], |
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| 250 | "endvals":{ |
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| 251 | "s1":"ahhhhd", |
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| 252 | "s1_mid":"hhhh" |
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| 253 | } |
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| 254 | }, |
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| 255 | { "code":["s1_mid = \"i\";"], |
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| 256 | "endvals":{ |
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| 257 | "s1":"aid", |
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| 258 | "s1_mid":"i" |
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| 259 | } |
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| 260 | }, |
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| 261 | { "code":["s1_mid = \"\";"], |
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| 262 | "endvals":{ |
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| 263 | "s1":"ad" |
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| 264 | } |
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| 265 | }, |
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| 266 | { "code":["s1_mid = \"jj\";"], |
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| 267 | "endvals":{ |
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| 268 | "s1":"ajjd", |
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| 269 | "s1_mid":"jj" |
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| 270 | } |
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| 271 | } |
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| 272 | ] |
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| 273 | }, |
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| 274 | { "type":"text", |
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| 275 | "value":"Multiple portions can be aliased. When there are several aliasing substrings at once, the text editor analogy becomes an online multi-user editor. I should be able to edit a paragraph in one place (changing the document's length), without my edits affecting which letters are within a mouse-selection that you had made previously, somewhere else." |
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| 276 | }, |
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| 277 | { "type":"demo", |
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| 278 | "vars":["s1", "s1_bgn", "s1_mid", "s1_end"], |
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| 279 | "steps":[ |
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| 280 | { "code":["string s1_bgn = s1(0, 1)`shareEdits;", |
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| 281 | "string s1_end = s1(3, 4)`shareEdits;"], |
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| 282 | "endvals":{ |
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| 283 | "s1":"ajjd", |
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| 284 | "s1_bgn":"a", |
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| 285 | "s1_mid":"jj", |
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| 286 | "s1_end":"d" |
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| 287 | } |
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| 288 | }, |
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| 289 | { "code":["s1_bgn = \"zzzz\";"], |
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| 290 | "endvals":{ |
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| 291 | "s1":"zzzzjjd", |
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| 292 | "s1_bgn":"zzzz", |
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| 293 | "s1_mid":"jj", |
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| 294 | "s1_end":"d" |
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| 295 | } |
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| 296 | } |
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| 297 | ] |
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| 298 | }, |
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| 299 | { "type":"text", |
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| 300 | "value":"When an edit happens on an aliasing substring that overlaps another, an effect is unavoidable. Here, the passive party sees its selection shortened, to exclude the characters that were not part of the original selection." |
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| 301 | }, |
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| 302 | { "type":"demo", |
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| 303 | "vars":["s1", "s1_bgn", "s1_crs", "s1_mid", "s1_end"], |
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| 304 | "steps":[ |
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| 305 | { "code":["string s1_crs = s1(3, 5)`shareEdits;"], |
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| 306 | "endvals":{ |
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| 307 | "s1":"zzzzjjd", |
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| 308 | "s1_bgn":"zzzz", |
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| 309 | "s1_crs":"zj", |
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| 310 | "s1_mid":"jj", |
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| 311 | "s1_end":"d" |
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| 312 | } |
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| 313 | }, |
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| 314 | { "code":["s1_crs = \"+++\";"], |
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| 315 | "endvals":{ |
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| 316 | "s1":"zzz+++jd", |
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| 317 | "s1_bgn":"zzz", |
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| 318 | "s1_crs":"+++", |
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| 319 | "s1_mid":"j", |
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| 320 | "s1_end":"d" |
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| 321 | } |
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| 322 | } |
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| 323 | ] |
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| 324 | }, |
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| 325 | { "type":"text", |
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| 326 | "value":"This shortening behaviour means that a modification has to occur entirely inside a substring, to show up in that substring. Sharing changes through the intersection of partially overlapping aliases is still possible, so long as the receiver's boundary is not inside the edit." |
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| 327 | }, |
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| 328 | { "type":"demo", |
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| 329 | "vars":["word", "consonants", "miniscules"], |
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| 330 | "steps":[ |
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| 331 | { "code":["string word = \"Phi\";", |
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| 332 | "string consonants = word(0,2)`shareEdits;", |
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| 333 | "string miniscules = word(1,3)`shareEdits;"], |
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| 334 | "endvals":{ |
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| 335 | "word":"Phi", |
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| 336 | "consonants":"Ph", |
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| 337 | "miniscules":"hi" |
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| 338 | } |
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| 339 | }, |
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| 340 | { "code":["consonants[1] = 's';"], |
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| 341 | "endvals":{ |
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| 342 | "word":"Psi", |
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| 343 | "consonants":"Ps", |
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| 344 | "miniscules":"si" |
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| 345 | } |
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| 346 | } |
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| 347 | ] |
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| 348 | }, |
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| 349 | { "type":"text", |
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| 350 | "value":"The extreme form of this shortening happens when a bystander alias is a proper substring of an edit. The bystander becomes an empty substring." |
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| 351 | }, |
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| 352 | { "type":"demo", |
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| 353 | "vars":["all", "greet", "greet_bgn", "greet_end"], |
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| 354 | "steps":[ |
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| 355 | { "code":["string all = \"They said hello again\";", |
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| 356 | "string greet = all(10,15)`shareEdits;", |
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| 357 | "string greet_bgn = all(10,11)`shareEdits;", |
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| 358 | "string greet_end = all(14,15)`shareEdits;"], |
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| 359 | "endvals":{ |
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| 360 | "all":"They said hello again", |
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| 361 | "greet":"hello", |
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| 362 | "greet_bgn":"h", |
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| 363 | "greet_end":"o" |
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| 364 | } |
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| 365 | }, |
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| 366 | { "code":["greet = \"sup\";"], |
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| 367 | "endvals":{ |
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| 368 | "all":"They said sup again", |
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| 369 | "greet":"sup" |
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| 370 | } |
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| 371 | } |
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| 372 | ] |
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| 373 | }, |
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| 374 | { "type":"text", |
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| 375 | "value":"As in the earlier step where \\emph{aj} becomes \\emph{ajjd}, such empty substrings maintain their places in the total string, and can be used for filling it. Because @greet_bgn@ was orginally at the start of the edit, in the outcome, the empty @greet_bgn@ sits just before the written value. Similarly @greed_end@ goes after. Though not shown, an overwritten substring at neither side goes arbitrarily to the before side." |
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| 376 | }, |
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| 377 | { "type":"demo", |
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| 378 | "vars":["all", "greet", "greet_bgn", "greet_end"], |
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| 379 | "steps":[ |
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| 380 | { "code":["greet_bgn = \"what\"; "], |
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| 381 | "endvals":{ |
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| 382 | "all":"They said whatsup again", |
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| 383 | "greet":"sup", |
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| 384 | "greet_bgn":"what" |
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| 385 | } |
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| 386 | }, |
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| 387 | { "code":["greet_end = \"...\"; "], |
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| 388 | "endvals":{ |
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| 389 | "all":"They said whatsup... again", |
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| 390 | "greet":"sup", |
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| 391 | "greet_bgn":"what", |
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| 392 | "greet_end":"..." |
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| 393 | } |
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| 394 | } |
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| 395 | ] |
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| 396 | }, |
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| 397 | { "type":"text", |
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| 398 | "value":"Though these empty substrings hold their places in the total string, an empty string only belongs to bigger strings when it occurs completely inside them. There is no such state as including an empty substring at an edge. For this reason, @word@ gains the characters added by assigning to @greet_bgn@ and @greet_end@, but the string @greet@ does not." |
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| 399 | } |
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| 400 | |
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| 401 | |
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| 402 | ] |
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| 403 | } |
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