├── go.mod ├── .gitignore ├── rope_reader.go ├── README.md ├── rope_test.go ├── rope.go └── LICENSE /go.mod: -------------------------------------------------------------------------------- 1 | module github.com/deadpixi/rope 2 | 3 | go 1.18 4 | -------------------------------------------------------------------------------- /.gitignore: -------------------------------------------------------------------------------- 1 | # Binaries for programs and plugins 2 | *.exe 3 | *.exe~ 4 | *.dll 5 | *.so 6 | *.dylib 7 | 8 | # Test binary, built with `go test -c` 9 | *.test 10 | 11 | # Output of the go coverage tool, specifically when used with LiteIDE 12 | *.out 13 | 14 | # Dependency directories (remove the comment below to include it) 15 | # vendor/ 16 | -------------------------------------------------------------------------------- /rope_reader.go: -------------------------------------------------------------------------------- 1 | package rope 2 | 3 | import ( 4 | "io" 5 | ) 6 | 7 | // A Reader provides an implementation of io.Reader for ropes. 8 | type Reader struct { 9 | rope Rope 10 | position int64 11 | } 12 | 13 | // Return a new reader attached to the given rope. 14 | func NewReader(rope Rope) *Reader { 15 | return rope.Reader() 16 | } 17 | 18 | // Read implements the standard Read interface: 19 | // it reads data from the rope, populating p, and returns 20 | // the number of bytes actually read. 21 | func (reader *Reader) Read(p []byte) (n int, err error) { 22 | n, err = reader.rope.ReadAt(p, reader.position) 23 | if err == nil { 24 | reader.position += int64(n) 25 | } 26 | return 27 | } 28 | 29 | // Return a new Reader attached to this rope. 30 | func (rope Rope) Reader() *Reader { 31 | return rope.OffsetReader(0) 32 | } 33 | 34 | func (rope Rope) OffsetReader(offset int) *Reader { 35 | return &Reader{rope: rope, position: int64(offset)} 36 | } 37 | 38 | // ReadAt implements the standard ReadAt interface: 39 | // it reads len(p) bytes from offset off into p, and returns 40 | // the number of bytes actually read. If n < len(p), err will 41 | // explain the shortfall. 42 | func (rope Rope) ReadAt(p []byte, off int64) (n int, err error) { 43 | o := int(off) 44 | for n < len(p) && o+n < rope.Length() { 45 | leaf, at := rope.leafForOffset(o + n) 46 | n += copy(p[n:], leaf.content[at:]) 47 | } 48 | 49 | if n < len(p) { 50 | err = io.EOF 51 | } 52 | 53 | return 54 | } 55 | -------------------------------------------------------------------------------- /README.md: -------------------------------------------------------------------------------- 1 | # Ropes in Go 2 | 3 | A value-oriented, immutable, functional rope in Go. 4 | 5 | # Introduction 6 | 7 | This module provides an implementation of the [rope data structure](https://en.wikipedia.org/wiki/Rope_(data_structure)) in Go. 8 | Ropes allow for the efficient manipulation of long strings of text. 9 | 10 | The rope structure implemented by this module is immutable, value-oriented, and immutable. 11 | 12 | There is no way to modify an existing rope: 13 | all operations on a rope return a new rope. 14 | 15 | One notable use case that this makes particularly nice is undo/redo: 16 | simply keep the old versions of the rope around. 17 | 18 | # Example 19 | 20 | A simple example: 21 | 22 | ```go 23 | 24 | rope := NewString("hello") 25 | rope = rope.AppendString(", world!") 26 | fmt.Printf("The value of the rope is: %v\n", rope.String()) 27 | 28 | ``` 29 | 30 | # Documentation 31 | 32 | Documentation is included inline and is also available at https://pkg.go.dev/github.com/deadpixi/rope 33 | 34 | # License 35 | 36 | rope - a persistent rope data structure 37 | Copyright (C) 2022 Rob King 38 | 39 | This library is free software; you can redistribute it and/or 40 | modify it under the terms of the GNU Lesser General Public 41 | License as published by the Free Software Foundation; either 42 | version 2.1 of the License, or (at your option) any later version. 43 | 44 | This library is distributed in the hope that it will be useful, 45 | but WITHOUT ANY WARRANTY; without even the implied warranty of 46 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 47 | Lesser General Public License for more details. 48 | 49 | You should have received a copy of the GNU Lesser General Public 50 | License along with this library; if not, write to the Free Software 51 | Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 52 | USA 53 | -------------------------------------------------------------------------------- /rope_test.go: -------------------------------------------------------------------------------- 1 | package rope 2 | 3 | import ( 4 | "bufio" 5 | "fmt" 6 | "io" 7 | "strings" 8 | "testing" 9 | ) 10 | 11 | func expectString(a, b string, t *testing.T) { 12 | if a != b { 13 | t.Fatalf("expected '%v', got '%v'", a, b) 14 | } 15 | } 16 | 17 | func expectInt(a, b int, t *testing.T) { 18 | if a != b { 19 | t.Fatalf("expected %v, got %v", a, b) 20 | } 21 | } 22 | 23 | func TestAppend(t *testing.T) { 24 | rope := NewString("foo") 25 | expectString("foo", rope.String(), t) 26 | 27 | rope = rope.AppendString("bar") 28 | expectString("foobar", rope.String(), t) 29 | 30 | expectInt(6, rope.Length(), t) 31 | } 32 | 33 | func TestInsert(t *testing.T) { 34 | rope := NewString("hello") 35 | rope = rope.InsertString(rope.Length(), "world").InsertString(5, ", ") 36 | 37 | expectString("hello, world", rope.String(), t) 38 | 39 | rope = rope.InsertString(rope.Length(), "!") 40 | expectString("hello, world!", rope.String(), t) 41 | } 42 | 43 | func TestSplit(t *testing.T) { 44 | rope := NewString("how now") 45 | left, right := rope.Split(3) 46 | expectString("how", left.String(), t) 47 | expectString(" now", right.String(), t) 48 | } 49 | 50 | func TestSlice(t *testing.T) { 51 | rope := NewString("hello") 52 | expectString("ell", string(rope.Slice(1, 4)), t) 53 | 54 | rope1 := NewString("hel") 55 | rope2 := NewString("lo") 56 | rope3 := Rope{ 57 | depth: 1, 58 | length: rope1.length + rope2.length, 59 | left: &rope1, 60 | right: &rope2, 61 | } 62 | 63 | expectString("hello", rope3.String(), t) 64 | expectString("ell", string(rope3.Slice(1, 4)), t) 65 | expectString("ello", string(rope3.Slice(1, 40)), t) 66 | } 67 | 68 | func TestDelete(t *testing.T) { 69 | rope := NewString("how now brown cow") 70 | rope = rope.Delete(8, 6) 71 | 72 | expectString("how now cow", rope.String(), t) 73 | } 74 | 75 | func TestEqual(t *testing.T) { 76 | rope := NewString("how now brown cow") 77 | rope = rope.Delete(8, 6) 78 | 79 | if !rope.Equal(NewString("how now cow")) { 80 | t.Fatalf("expected ropes to be equal") 81 | } 82 | 83 | rope1 := NewString("hel") 84 | rope2 := NewString("lo") 85 | rope3 := Rope{ 86 | depth: 1, 87 | length: rope1.length + rope2.length, 88 | left: &rope1, 89 | right: &rope2, 90 | } 91 | 92 | rope4 := NewString("hel") 93 | rope5 := NewString("lo") 94 | rope6 := Rope{ 95 | depth: 1, 96 | length: rope1.length + rope2.length, 97 | left: &rope4, 98 | right: &rope5, 99 | } 100 | 101 | if !rope6.Equal(rope3) { 102 | t.Fatalf("expected ropes to be equal") 103 | } 104 | 105 | expectString("hello", rope6.String(), t) 106 | expectString("hello", rope3.String(), t) 107 | 108 | ropeX := NewString(strings.Repeat("A", 4097)).AppendString(strings.Repeat("A", 1137)) 109 | ropeY := NewString(strings.Repeat("A", 1137)).AppendString(strings.Repeat("A", 4097)) 110 | if !ropeX.Equal(ropeY) { 111 | t.Fatalf("expected ropes to be equal") 112 | } 113 | 114 | ropeX = ropeX.AppendString("X") 115 | ropeY = ropeY.AppendString("Y") 116 | if ropeX.Equal(ropeY) { 117 | t.Fatalf("expected ropes not to be equal") 118 | } 119 | } 120 | 121 | func refer(rope Rope) *Rope { 122 | return &rope 123 | } 124 | 125 | func TestBalance(t *testing.T) { 126 | rope := NewString("hello") 127 | for i := 0; i < 32; i++ { 128 | newRope := New() 129 | rope = Rope{ 130 | length: 5, 131 | depth: i + 1, 132 | left: refer(rope), // this is such a hack 133 | right: &newRope, 134 | } 135 | } 136 | 137 | expectString("hello", rope.String(), t) 138 | 139 | if rope.isBalanced() { 140 | t.Fatalf("expected rope to be unbalanced") 141 | } 142 | 143 | rope = rope.Rebalance() 144 | 145 | if !rope.isBalanced() { 146 | t.Fatalf("expected rope to be balanced") 147 | } 148 | 149 | expectString("hello", rope.String(), t) 150 | expectInt(5, rope.Length(), t) 151 | } 152 | 153 | func TestBigString(t *testing.T) { 154 | rope := New() 155 | for i := 0; i < 65536; i++ { 156 | rope = rope.AppendString("aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa") 157 | } 158 | 159 | rope = rope.Rebalance() 160 | if !rope.isBalanced() { 161 | t.Fatalf("expected rope to be balanced") 162 | } 163 | 164 | for i := 1; i < 11; i++ { 165 | rope = rope.InsertString(65536/i, "foo") 166 | } 167 | 168 | rope = rope.Rebalance() 169 | if !rope.isBalanced() { 170 | t.Fatalf("expected rope to be balanced") 171 | } 172 | } 173 | 174 | func TestReadAt(t *testing.T) { 175 | scottishPlay := `She should have died hereafter; 176 | There would have been a time for such a word. 177 | — To-morrow, and to-morrow, and to-morrow, 178 | Creeps in this petty pace from day to day, 179 | To the last syllable of recorded time; 180 | And all our yesterdays have lighted fools 181 | The way to dusty death. Out, out, brief candle! 182 | Life's but a walking shadow, a poor player 183 | That struts and frets his hour upon the stage 184 | And then is heard no more. It is a tale 185 | Told by an idiot, full of sound and fury 186 | Signifying nothing.` 187 | 188 | rope := NewString("") 189 | scanner := bufio.NewScanner(strings.NewReader(scottishPlay)) 190 | for scanner.Scan() { 191 | rope = rope.AppendString(scanner.Text()) 192 | } 193 | 194 | buf := make([]byte, 1000) 195 | _, err := rope.ReadAt(buf, 120) 196 | if err != io.EOF { 197 | t.Fatalf("expected EOF error") 198 | } 199 | 200 | expectString("Creeps in this petty pace from day to day,To the last syllable of recorded time;", string(buf)[:80], t) 201 | 202 | buf = make([]byte, 41) 203 | _, err = rope.ReadAt(buf, 120) 204 | if err != nil { 205 | t.Fatalf("expected no error, got: %v", err) 206 | } 207 | 208 | expectString("Creeps in this petty pace from day to day", string(buf), t) 209 | } 210 | 211 | func TestReadAtCrossingLeaves(t *testing.T) { 212 | var builder strings.Builder 213 | 214 | rope := New() 215 | for i := 0; i < 65535; i++ { 216 | rope = rope.AppendString(fmt.Sprintf("%v:", i)) 217 | builder.WriteString(fmt.Sprintf("%v:", i)) 218 | } 219 | 220 | canon := builder.String() 221 | 222 | buf := make([]byte, 20) 223 | rope.ReadAt(buf, 4090) 224 | 225 | expectString("1040:1041:1042:1043:", string(buf), t) 226 | expectString("1040:1041:1042:1043:", canon[4090:4090+20], t) 227 | } 228 | 229 | func TestReaderFrom(t *testing.T) { 230 | var builder strings.Builder 231 | 232 | rope := NewString("foo\nbar\nbaz\nquux\n") 233 | scanner := bufio.NewScanner(rope.OffsetReader(4)) 234 | 235 | for scanner.Scan() { 236 | builder.WriteString(scanner.Text() + ":") 237 | } 238 | 239 | expectString("bar:baz:quux:", builder.String(), t) 240 | } 241 | -------------------------------------------------------------------------------- /rope.go: -------------------------------------------------------------------------------- 1 | // The rope package provides an immutable, value-oriented Rope. 2 | // Ropes allow large sequences of text to be manipulated efficiently. 3 | package rope 4 | 5 | import ( 6 | "bytes" 7 | "strings" 8 | ) 9 | 10 | const ( 11 | maxDepth = 64 12 | maxLeafSize = 4096 13 | ) 14 | 15 | // A Rope is a data structure for storing long runs of text. 16 | // Ropes are persistent: there is no way to modify an existing rope. 17 | // Instead, all operations return a new rope with the requested changes. 18 | // 19 | // This persistence makes it easy to store old versions of a Rope just by holding on to old roots. 20 | type Rope struct { 21 | content string 22 | length, depth int 23 | left, right *Rope 24 | } 25 | 26 | // Return a new empty rope. 27 | func New() Rope { 28 | return Rope{} 29 | } 30 | 31 | // Return a new rope with the contents of string s. 32 | func NewString(s string) Rope { 33 | return Rope{content: s, length: len(s)} 34 | } 35 | 36 | // Notice that all of the methods take and return ropes by value. 37 | // This is slightly less efficient than if we'd done pointers, but it 38 | // seems cleaner from a "persistent data structure" point of view. 39 | 40 | func (rope Rope) concat(other Rope) Rope { 41 | switch { 42 | case rope.length == 0: 43 | return other 44 | case other.length == 0: 45 | return rope 46 | case rope.length+other.length <= maxLeafSize: 47 | return NewString(rope.String() + other.String()) 48 | default: 49 | depth := rope.depth 50 | if other.depth > depth { 51 | depth = other.depth 52 | } 53 | return Rope{ 54 | length: rope.length + other.length, 55 | depth: depth + 1, 56 | left: &rope, 57 | right: &other, 58 | } 59 | } 60 | } 61 | 62 | // Return a new rope that is the concatenation of this rope and the other rope. 63 | func (rope Rope) Append(other Rope) Rope { 64 | return rope.concat(other).rebalanceIfNeeded() 65 | } 66 | 67 | // Return a new rope that is the concatenation of this rope and string s. 68 | func (rope Rope) AppendString(other string) Rope { 69 | return rope.Append(NewString(other)) 70 | } 71 | 72 | // Return a new rope with length bytes at offset deleted. 73 | func (rope Rope) Delete(offset, length int) Rope { 74 | if length == 0 || offset == rope.length { 75 | return rope 76 | } 77 | 78 | left, right := rope.Split(offset) 79 | _, newRight := right.Split(length) 80 | return left.Append(newRight) 81 | } 82 | 83 | // Returns true if this rope is equal to other. 84 | func (rope Rope) Equal(other Rope) bool { 85 | if rope == other { 86 | return true 87 | } 88 | 89 | if rope.length != other.length { 90 | return false 91 | } 92 | 93 | for i := 0; i < rope.length; i += maxLeafSize { 94 | if !bytes.Equal(rope.Slice(i, i+maxLeafSize), other.Slice(i, i+maxLeafSize)) { 95 | return false 96 | } 97 | } 98 | 99 | return true 100 | } 101 | 102 | // Return a new rope with the contents of other inserted at the given index. 103 | func (rope Rope) Insert(at int, other Rope) Rope { 104 | switch at { 105 | case 0: 106 | return other.Append(rope) 107 | case rope.length: 108 | return rope.Append(other) 109 | default: 110 | left, right := rope.Split(at) 111 | return left.concat(other).Append(right) 112 | } 113 | } 114 | 115 | // Return a new rope with the contents of string other inserted at the given index. 116 | func (rope Rope) InsertString(at int, other string) Rope { 117 | return rope.Insert(at, NewString(other)) 118 | } 119 | 120 | // Return the length of the rope in bytes. 121 | func (rope Rope) Length() int { 122 | return rope.length 123 | } 124 | 125 | // Return a new version of this rope that is balanced for better performance. 126 | // Generally speaking, this will be invoked automatically during the course of other operations and 127 | // thus only needs to be called if you know you'll be generating a lot of unbalanced ropes. 128 | func (rope Rope) Rebalance() Rope { 129 | if rope.isBalanced() { 130 | return rope 131 | } 132 | 133 | var leaves []Rope 134 | rope.walk(func(node Rope) { 135 | leaves = append(leaves, node) 136 | }) 137 | 138 | return merge(leaves, 0, len(leaves)) 139 | } 140 | 141 | // Return the bytes in [a, b) 142 | func (rope Rope) Slice(a, b int) []byte { 143 | p := make([]byte, b-a) 144 | n, _ := rope.ReadAt(p, int64(a)) 145 | return p[:n] 146 | } 147 | 148 | // Returns two new ropes, one containing the content to the left of the given index and the other the content to the right. 149 | func (rope Rope) Split(at int) (Rope, Rope) { 150 | switch { 151 | case rope.isLeaf(): 152 | return NewString(rope.content[0:at]), NewString(rope.content[at:]) 153 | 154 | case at == 0: 155 | return Rope{}, rope 156 | 157 | case at == rope.length: 158 | return rope, Rope{} 159 | 160 | case at < rope.left.length: 161 | left, right := rope.left.Split(at) 162 | return left, right.Append(*rope.right) 163 | 164 | case at > rope.left.length: 165 | left, right := rope.right.Split(at - rope.left.length) 166 | return rope.left.Append(left), right 167 | 168 | default: 169 | return *rope.left, *rope.right 170 | } 171 | } 172 | 173 | // Return the contents of the rope as a string. 174 | func (rope Rope) String() string { 175 | if rope.isLeaf() { 176 | return rope.content 177 | } 178 | 179 | var builder strings.Builder 180 | rope.walk(func(node Rope) { 181 | builder.WriteString(node.content) 182 | }) 183 | 184 | return builder.String() 185 | } 186 | 187 | func (rope Rope) isBalanced() bool { 188 | switch { 189 | case rope.isLeaf(): 190 | return true 191 | case rope.depth >= len(fibonacci)-2: 192 | return false 193 | default: 194 | return fibonacci[rope.depth+2] <= rope.length 195 | } 196 | } 197 | 198 | func (rope Rope) isLeaf() bool { 199 | return rope.left == nil 200 | } 201 | 202 | func (rope Rope) leafForOffset(at int) (Rope, int) { 203 | switch { 204 | case rope.isLeaf(): 205 | return rope, at 206 | case at < rope.left.length: 207 | return rope.left.leafForOffset(at) 208 | default: 209 | return rope.right.leafForOffset(at - rope.left.length) 210 | } 211 | } 212 | 213 | func (rope Rope) rebalanceIfNeeded() Rope { 214 | if rope.isBalanced() || abs(rope.left.depth-rope.right.depth) < maxDepth { 215 | return rope 216 | } 217 | 218 | return rope.Rebalance() 219 | } 220 | 221 | func (rope Rope) walk(callback func(Rope)) { 222 | if rope.isLeaf() { 223 | callback(rope) 224 | } else { 225 | rope.left.walk(callback) 226 | rope.right.walk(callback) 227 | } 228 | } 229 | 230 | func abs(a int) int { 231 | if a < 0 { 232 | return -a 233 | } 234 | return a 235 | } 236 | 237 | func merge(leaves []Rope, start, end int) Rope { 238 | length := end - start 239 | switch length { 240 | case 1: 241 | return leaves[start] 242 | case 2: 243 | return leaves[start].concat(leaves[start+1]) 244 | default: 245 | mid := start + length/2 246 | return merge(leaves, start, mid).concat(merge(leaves, mid, end)) 247 | } 248 | } 249 | 250 | var fibonacci []int 251 | 252 | func init() { 253 | // The heurstic for whether a rope is balanced depends on the Fibonacci sequence; 254 | // we initialize the table of Fibonacci numbers here. 255 | first := 0 256 | second := 1 257 | 258 | for c := 0; c < maxDepth+3; c++ { 259 | next := 0 260 | if c <= 1 { 261 | next = c 262 | } else { 263 | next = first + second 264 | first = second 265 | second = next 266 | } 267 | fibonacci = append(fibonacci, next) 268 | } 269 | } 270 | -------------------------------------------------------------------------------- /LICENSE: -------------------------------------------------------------------------------- 1 | GNU LESSER GENERAL PUBLIC LICENSE 2 | Version 2.1, February 1999 3 | 4 | Copyright (C) 1991, 1999 Free Software Foundation, Inc. 5 | 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA 6 | Everyone is permitted to copy and distribute verbatim copies 7 | of this license document, but changing it is not allowed. 8 | 9 | [This is the first released version of the Lesser GPL. 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