toktrie - Token utility library

This crate provides a utility library for working with tokens and token tries.

Byte stack interface

The constraints are typically expressed on strings or bytes, not tokens. To compute the set of tokens that match a string constraint, one needs go through all the possible tokens and apply the constraint. An efficient way to do this is walk a prefix tree (trie) of all tokens. This library implements this trie and exposes a way of filtering when provided with a constraints implementing the following interface:

pub trait Recognizer {
    /// If `stack.top()` transitions via `byte` to `X`, execute `stack.push(X)`.
    fn push_byte(&mut self, byte: u8);
    /// for _ in 0..num { stack.pop() }
    fn pop_bytes(&mut self, num: usize);
    /// X = stack.top(); stack.empty(); stack.push(X)
    fn collapse(&mut self);
    /// check if stack.top() transitions via byte to a viable state
    fn byte_allowed(&mut self, byte: u8) -> bool;
    /// check if stack.top() transitions via tok to a viable state
    fn special_allowed(&mut self, tok: SpecialToken) -> bool;
    /// Called when iteration over the trie is finished
    /// Stack has exactly one element then.
    fn trie_finished(&mut self);
    /// This combines `push_byte` and `byte_allowed` into one function for performance.
    fn try_push_byte(&mut self, byte: u8) -> bool;
}

The AiciRecognizer struct converts Recognizer to AiciCtrl.

Functional byte interface

The following interface can be transformed into Recognizer using StackRecognizer struct.

pub trait FunctionalRecognizer<S: Copy> {
    /// Initial state
    fn initial(&self) -> S;
    /// Extend the recognizer with given byte.
    fn append(&self, state: S, byte: u8) -> S;
    /// Check if given byte is allowed in given state.
    fn byte_allowed(&self, state: S, byte: u8) -> bool;
    /// Check if given special token is allowed in given state.
    fn special_allowed(&self, state: S, tok: SpecialToken) -> bool;
}

These three layers add up to about 40k of compiled code (Wasm).

Contributing

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Trademarks

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