Necessary Pigeonholing Mechanism

    dfa

    1.2.0 • Public • Published

    dfa

    Compiles a regular expression like syntax to fast deterministic finite automata. Useful for pattern matching against non-string sequences.

    Example

    This example matches Hangul syllables. The symbols defined in the machine are Unicode character categories which could be mapped from code points.

    Machine definition:

    # define symbols 
    X   = 0; # Other character 
    L   = 1; # Leading consonant 
    V   = 2; # Medial vowel 
    T   = 3; # Trailing consonant 
    LV  = 4; # Composed <LV> syllable 
    LVT = 5; # Composed <LVT> syllable 
    M   = 6; # Tone mark 
     
    # define variables 
    decomposed = L V T?;
    partial = LV T?;
    composed = LVT;
     
    # define main state machine pattern 
    main = (decomposed | partial | composed) M?;

    Visualized, the machine looks like this (double circles are accepting states):

    dfa

    Compiling and using the machine:

    import compile from 'dfa/compile';
    import fs from 'fs';
     
    let stateMachine = compile(fs.readFileSync('hangul.machine', 'utf8'));
     
    // find matches
    for (let [startIndex, endIndex] of stateMachine.match([0, 1, 2, 3, 0, 4, 6]) {
      console.log('match:', startIndex, endIndex);
    }

    Output:

    match: 1 3
    match: 5 6
    

    Syntax

    A state machine file contains a list of assignment statements. Comments are also allowed and are started with the # character. Each statement is an assignment of a variable name to a value or expression. Assigning a variable to a number produces a symbol, which is added to the state machine's alphabet. Assigning a variable to an expression allows for substitutions into later expressions. The special main variable should always be assigned to at the end of the file, and is the final expression that will be compiled.

    A subset of common regular expression syntax is supported. A list of operators and their precedence is below. Operators with the same precedence are evaluated left to right.

    Precedence Syntax Type Meaning
    1 a \| b Alternation Matches either a or b
    2 a b Concatenation Matches a followed by b
    3 a* Repetition Matches zero or more occurrences of a
    3 a+ Repetition Matches one ore more occurrences of a
    3 a? Optional Matches zero or one occurrence of a
    3 a{n} Repetition Matches exactly n occurrences of a
    3 a{n,} Repetition Matches n or more occurrences of a
    3 a{,n} Repetition Matches up to n occurrences of a
    3 a{n,m} Repetition Matches n to m occurrences of a
    4 t:<expr> Tag Tags the following expression with tag t
    5 (<expr>) Grouping Groups an expression

    License

    MIT

    Install

    npm i dfa

    DownloadsWeekly Downloads

    810,009

    Version

    1.2.0

    License

    MIT

    Unpacked Size

    138 kB

    Total Files

    6

    Last publish

    Collaborators

    • devongovett