Clarity Pattern Parser

A powerful pattern matching and parsing library that provides a flexible grammar for defining complex patterns. Perfect for building parsers, validators, and text processing tools.

Try it online! 🚀 Open in Playground

Features

🎯 Flexible pattern matching with both grammar and direct API
🔄 Support for recursive patterns and expressions
🎨 Customizable pattern composition
🚀 High performance parsing
🔍 Built-in debugging support
📝 Rich AST manipulation capabilities
🔌 Extensible through custom patterns and decorators

Installation

npm install clarity-pattern-parser

Quick Start

Using Grammar

import { patterns } from "clarity-pattern-parser";

// Define patterns using grammar
const { fullName } = patterns`
    first-name = "John"
    last-name = "Doe"
    space = /\s+/
    full-name = first-name + space + last-name
`;

// Execute pattern
const result = fullName.exec("John Doe");
console.log(result.ast?.value); // "John Doe"

Using Direct API

import { Literal, Sequence } from "clarity-pattern-parser";

// Create patterns directly
const firstName = new Literal("first-name", "John");
const space = new Literal("space", " ");
const lastName = new Literal("last-name", "Doe");
const fullName = new Sequence("full-name", [firstName, space, lastName]);

// Execute pattern
const result = fullName.exec("John Doe");
console.log(result.ast?.value); // "John Doe"

Online Playground

Try Clarity Pattern Parser in your browser with our interactive playground:

Open in Playground

The playground allows you to:

Write and test patterns in real-time
See the AST visualization
Debug pattern execution
Share patterns with others
Try out different examples

Grammar Documentation
Direct Pattern Usage
Advanced Topics

Grammar Documentation

This document describes the grammar features supported by the Clarity Pattern Parser.

Basic Patterns

Literal Strings

Define literal string patterns using double quotes:

name = "John"

Escaped characters are supported in literals:

\n - newline
\r - carriage return
\t - tab
\b - backspace
\f - form feed
\v - vertical tab
\0 - null character
\x00 - hex character
\u0000 - unicode character
\" - escaped quote
\\ - escaped backslash

Regular Expressions

Define regex patterns using forward slashes:

name = /\w/

Pattern Operators

Options (|)

Match one of multiple patterns using the | operator. This is used for simple alternatives where order doesn't matter:

names = john | jane

Expression (|)

Expression patterns also use the | operator but are used for defining operator precedence in expressions. The order of alternatives determines precedence, with earlier alternatives having higher precedence. By default, operators are left-associative.

Example of an arithmetic expression grammar:

prefix-operators = "+" | "-"
prefix-expression = prefix-operators + expression
postfix-operators = "++" | "--"
postfix-expression = expression + postfix-operators
add-sub-operators = "+" | "-"
add-sub-expression = expression + add-sub-operators + expression
mul-div-operators = "*" | "/"
mul-div-expression = expression + mul-div-operators + expression
expression = prefix-expression | mul-div-expression | add-sub-expression | postfix-expression

Repetition

Basic Repeat

Repeat a pattern one or more times using +:

digits = (digit)+

Zero or More

Repeat a pattern zero or more times using *:

digits = (digit)*

Bounded Repetition

Specify exact repetition counts using curly braces:

{n} - Exactly n times: (pattern){3}
{n,} - At least n times: (pattern){1,}
{,n} - At most n times: (pattern){,3}
{n,m} - Between n and m times: (pattern){1,3}

Repetition with Divider

Repeat patterns with a divider between occurrences:

digits = (digit, comma){3}

Add trim keyword to trim the divider from the end:

digits = (digit, comma trim)+

Imports and Parameters

Basic Import

Import patterns from other files:

import { pattern-name } from "path/to/file.cpat"

Import with Parameters

Import with custom parameters:

import { pattern } from "file.cpat" with params {
  custom-param = "value"
}

Parameter Declaration

Declare parameters that can be passed to the grammar:

use params {
  param-name
}

Default Parameters

Specify default values for parameters:

use params {
  param = default-value
}

Decorators

Token Decorator

Specify tokens for a pattern:

@tokens([" "])
spaces = /\s+/

Custom Decorators

Support for custom decorators with various argument types:

@decorator()  // No arguments
@decorator(["value"])  // Array argument
@decorator({"prop": value})  // Object argument

Comments

Add comments using the # symbol:

# This is a comment
pattern = "value"

Pattern References

Reference other patterns by name:

pattern1 = "value"
pattern2 = pattern1

Pattern Aliasing

Import patterns with aliases:

import { original as alias } from "file.cpat"

String Template Patterns

Patterns can be defined inline using string templates. This allows for quick pattern definition and testing without creating separate files.

Basic Example

const { fullName } = patterns`
    first-name = "John"
    last-name = "Doe"
    space = /\s+/
    full-name = first-name + space + last-name
`;

const result = fullName.exec("John Doe");
// result.ast.value will be "John Doe"

Complex Example (HTML-like Markup)

const { body } = patterns`
    tag-name = /[a-zA-Z_-]+[a-zA-Z0-9_-]*/
    ws = /\s+/
    opening-tag = "<" + tag-name + ws? + ">"
    closing-tag = "</" + tag-name + ws? + ">"
    child = ws? + element + ws?
    children = (child)*
    element = opening-tag + children + closing-tag
    body = ws? + element + ws?
`;

const result = body.exec(`
    <div>
        <div></div>
        <div></div>    
    </div>
`, true);

// Clean up spaces from the AST
result?.ast?.findAll(n => n.name.includes("ws")).forEach(n => n.remove());
// result.ast.value will be "<div><div></div><div></div></div>"

Direct Pattern Usage

While the grammar provides a convenient way to define patterns, you can also use the Pattern classes directly for more control and flexibility.

Basic Patterns

Literal

import { Literal } from "clarity-pattern-parser";

const firstName = new Literal("first-name", "John");
const result = firstName.exec("John");
// result.ast.value will be "John"

Regex

import { Regex } from "clarity-pattern-parser";

const digits = new Regex("digits", "\\d+");
const result = digits.exec("123");
// result.ast.value will be "123"

Composite Patterns

Sequence

import { Sequence, Literal } from "clarity-pattern-parser";

const firstName = new Literal("first-name", "John");
const space = new Literal("space", " ");
const lastName = new Literal("last-name", "Doe");
const fullName = new Sequence("full-name", [firstName, space, lastName]);

const result = fullName.exec("John Doe");
// result.ast.value will be "John Doe"

Options

import { Options, Literal } from "clarity-pattern-parser";

const john = new Literal("john", "John");
const jane = new Literal("jane", "Jane");
const names = new Options("names", [john, jane]);

const result = names.exec("Jane");
// result.ast.value will be "Jane"

Expression

import { Expression, Literal } from "clarity-pattern-parser";

const a = new Literal("a", "a");
const b = new Literal("b", "b");
const c = new Literal("c", "c");
const expression = new Expression("expression", [a, b, c]);

const result = expression.exec("a ? b : c");
// result.ast.value will be "a ? b : c"

Pattern Context

import { Context, Literal } from "clarity-pattern-parser";

const name = new Literal("name", "John");
const context = new Context("name-context", name);

const result = context.exec("John");
// result.ast.value will be "John"

Pattern Reference

import { Reference, Literal, Sequence } from "clarity-pattern-parser";

const name = new Literal("name", "John");
const reference = new Reference("name-ref", name);
const pattern = new Sequence("pattern", [reference]);

const result = pattern.exec("John");
// result.ast.value will be "John"

Pattern Execution

Pattern execution returns a ParseResult that includes the AST and any error information:

const result = pattern.exec("some text");
if (result.error) {
    console.error(result.error.message);
    console.error(result.error.expected);
    console.error(result.error.position);
} else {
    console.log(result.ast?.value);
}

AST Manipulation

The AST (Abstract Syntax Tree) returned by pattern execution can be manipulated:

const result = pattern.exec("some text");
if (result.ast) {
    // Find all nodes with a specific name
    const nodes = result.ast.findAll(n => n.name === "space");
    
    // Remove nodes
    nodes.forEach(n => n.remove());
    
    // Get the final value
    const value = result.ast.value;
}

Advanced Topics

Custom Patterns

You can create custom patterns by extending the base Pattern class:

import { Pattern } from "clarity-pattern-parser";

class CustomPattern extends Pattern {
    constructor(name: string) {
        super(name);
    }

    exec(text: string) {
        // Custom pattern implementation
    }
}

Performance Tips

Use test() instead of exec() when you only need to check if a pattern matches
Cache frequently used patterns
Use Reference for recursive patterns instead of direct recursion
Minimize the use of optional patterns in sequences
Use bounded repetition when possible

Debugging

Enable debug mode to get detailed information about pattern execution:

const result = pattern.exec("some text", true);
// Debug information will be available in result.debug

Error Handling

Pattern execution returns a ParseResult that includes error information:

const result = pattern.exec("invalid text");
if (result.error) {
    console.error(result.error.message);
    console.error(result.error.expected);
    console.error(result.error.position);
}

Examples

JSON Parser

const { json } = patterns`
    # Basic JSON grammar
    ws = /\s+/
    string = /"[^"]*"/
    number = /-?\d+(\.\d+)?/
    boolean = "true" | "false"
    null = "null"
    value = string | number | boolean | null | array | object
    array-items = (value, /\s*,\s*/)+
    array = "[" +ws? + array-items? + ws? + "]"
    object-property = string + ws? + ":" + ws? + value
    object-properties = (object-property, /\s*,\s*/ trim)+
    object = "{" + ws? + object-properties? + ws? + "}"
    json = ws? + value + ws?
`;

HTML Parser

const { html } = patterns`
    # Basic HTML grammar
    ws = /\s+/
    tag-name = /[a-zA-Z_-]+[a-zA-Z0-9_-]*/
    attribute-name = /[a-zA-Z_-]+[a-zA-Z0-9_-]*/
    attribute-value = /"[^"]*"/ 
    value-attribute = attribute-name + "=" + attribute-value
    bool-attribute = attribute-name
    attribute = value-attribute | bool-attribute
    attributes = (attribute, ws)*
    opening-tag = "<" + ws? + tag-name + ws? + attributes? + ">"
    closing-tag = "</" + ws? + tag-name + ws? + ">"
    text = /[^<]+/
    child = text | element
    children = (child, /\s*/)+
    element = opening-tag + children? + closing-tag
    html = ws? + element + ws?
`;

License

This project is licensed under the MIT License - see the LICENSE file for details.