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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,99 @@ | ||
| import { charToIndex, SKIExpression, SKIKey } from '../ski/expression.js'; | ||
| import { SKITrieNode } from './skiTrieNode.js'; | ||
|
|
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| /** | ||
| * A simple immutable SKI trie. | ||
| */ | ||
| export interface SKITrie { | ||
| root: SKITrieNode<SKIExpression>; | ||
| } | ||
|
|
||
| /** | ||
| * Creates a new SKI trie. | ||
| * If no root is provided, a root node with an empty prefix is created. | ||
| */ | ||
| export function createSKITrie(root?: SKITrieNode<SKIExpression>): SKITrie { | ||
| return { root: root ?? makeTrieNode<SKIExpression>([]) }; | ||
| } | ||
|
|
||
| /** | ||
| * Helper to create a new trie node. | ||
| * If no children array is provided, one with 5 slots is created. | ||
| */ | ||
| export function makeTrieNode<T>( | ||
| prefix: SKIKey, | ||
| value?: T, | ||
| children?: (SKITrieNode<T> | undefined)[] | ||
| ): SKITrieNode<T> { | ||
| return { | ||
| prefix, | ||
| value, | ||
| children: children ? children.slice() : new Array<SKITrieNode<T> | undefined>(5).fill(undefined) | ||
| }; | ||
| } | ||
|
|
||
| /** | ||
| * Returns a shallow copy of a node. | ||
| */ | ||
| function copyNode<T>(node: SKITrieNode<T>): SKITrieNode<T> { | ||
| return makeTrieNode(node.prefix.slice(), node.value, node.children); | ||
| } | ||
|
|
||
| /** | ||
| * Looks up the value associated with the given key. | ||
| * | ||
| * The key is an array of SKIChar. | ||
| */ | ||
| export function getSKITrie(trie: SKITrie, key: SKIKey): SKIExpression | undefined { | ||
| let node = trie.root; | ||
| // For each character in the key, descend one level. | ||
| for (const char of key) { | ||
| const idx = charToIndex(char); | ||
| const child = node.children[idx]; | ||
| if (!child) { | ||
| return undefined; | ||
| } | ||
| node = child; | ||
| } | ||
| return node.value; | ||
| } | ||
|
|
||
| /** | ||
| * Returns a new trie that maps the given key to the given value. | ||
| * Makes use of structural sharing to avoid duplicating nodes. | ||
| */ | ||
| export function setSKITrie(trie: SKITrie, key: SKIKey, value: SKIExpression): SKITrie { | ||
| // Special-case: an empty key updates the root. | ||
| if (key.length === 0) { | ||
| const newRoot = copyNode(trie.root); | ||
| newRoot.value = value; | ||
| return createSKITrie(newRoot); | ||
| } | ||
|
|
||
| // Start by copying the root. | ||
| const newRoot = copyNode(trie.root); | ||
| let current = newRoot; | ||
| // For each character in the key, descend into the appropriate child. | ||
| for (const char of key) { | ||
| const idx = charToIndex(char); | ||
| let child = current.children[idx]; | ||
| if (child) { | ||
| // Copy the child so as not to mutate the original structure. | ||
| child = copyNode(child); | ||
| } else { | ||
| // Create a new node for this character. | ||
| // (For non-root nodes the prefix is the one character of the key.) | ||
| child = makeTrieNode<SKIExpression>([char]); | ||
| } | ||
| // Replace the corresponding child pointer. | ||
| const newChildren = current.children.slice(); | ||
| newChildren[idx] = child; | ||
| current.children = newChildren; | ||
| // Move down the trie. | ||
| current = child; | ||
| } | ||
|
|
||
| // At the end of the key, set the value. | ||
| current.value = value; | ||
| return createSKITrie(newRoot); | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,26 @@ | ||
| import { SKIKey } from '../ski/expression.js'; | ||
|
|
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| /** | ||
| * A plain record representing a node in the SKI trie. | ||
| */ | ||
| export interface SKITrieNode<T> { | ||
| prefix: SKIKey; | ||
| value?: T; | ||
| children: (SKITrieNode<T> | undefined)[]; | ||
| } | ||
|
|
||
| /** | ||
| * Factory function to create a new SKI trie node. | ||
| * If children are not provided, a new 5-slot array filled with undefined is created. | ||
| */ | ||
| export function makeTrieNode<T>( | ||
| prefix: SKIKey, | ||
| value?: T, | ||
| children?: (SKITrieNode<T> | undefined)[] | ||
| ): SKITrieNode<T> { | ||
| return { | ||
| prefix, | ||
| value, | ||
| children: children ?? new Array<SKITrieNode<T> | undefined>(5).fill(undefined) | ||
| }; | ||
| } |
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