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

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.

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

In this example:

prefix-expression has highest precedence
mul-div-expression has next highest precedence
add-sub-expression has next highest precedence
postfix-expression has lowest precedence

To make an operator right-associative, add the right keyword:

expression = prefix-expression | mul-div-expression | add-sub-expression right | postfix-expression

Sequence (+)

Concatenate patterns in sequence using the + operator:

full-name = first-name + space + last-name

Optional (?)

Make a pattern optional using the ? operator:

full-name = first-name + space + middle-name? + last-name

Not (!)

Negative lookahead using the ! operator:

pattern = !excluded-pattern + actual-pattern

Take Until (?->|)

Match all characters until a specific pattern is found:

script-text = ?->| "</script"

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
}

Custom Grammar Resolvers

The Clarity Pattern Parser allows you to provide your own resolver for handling imports of .cpat files. This is useful when you need to load patterns from different sources like a database, network, or custom file system.

Basic Resolver Example

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

// Simple in-memory resolver
const pathMap: Record<string, string> = {
    "first-name.cpat": `first-name = "John"`,
    "space.cpat": `space = " "`
};

const resolver = (resource: string) => {
    return Promise.resolve({ 
        expression: pathMap[resource],
        resource 
    });
};

const patterns = await Grammar.parse(`
    import { first-name } from "first-name.cpat"
    import { space } from "space.cpat"
    last-name = "Doe"
    full-name = first-name + space + last-name
`, { resolveImport: resolver });

const result = patterns["full-name"].exec("John Doe");
// result.ast.value will be "John Doe"

Resolver with Parameters

const spaceExpression = `
    use params { custom-space }
    space = custom-space
`;

const pathMap: Record<string, string> = {
    "space.cpat": spaceExpression
};

const resolver = (resource: string) => {
    return Promise.resolve({ 
        expression: pathMap[resource],
        resource 
    });
};

const patterns = await Grammar.parse(`
    import { space } from "space.cpat" with params {
        custom-space = "  "
    }
    last-name = "Doe"
    full-name = first-name + space + last-name
`, { resolveImport: resolver });

const result = patterns["full-name"].exec("John  Doe");
// result.ast.value will be "John  Doe"

Resolver with Aliases

const pathMap: Record<string, string> = {
    "resource1.cpat": `value = "Value"`,
    "resource2.cpat": `
        use params { param }
        export-value = param
    `
};

const resolver = (resource: string) => {
    return Promise.resolve({ 
        expression: pathMap[resource],
        resource 
    });
};

const patterns = await Grammar.parse(`
    import { value as alias } from "resource1.cpat"
    import { export-value } from "resource2.cpat" with params {
        param = alias
    }
    name = export-value
`, { resolveImport: resolver });

const result = patterns["name"].exec("Value");
// result.ast.value will be "Value"

Resolver with Default Values

const resolver = (_: string) => {
    return Promise.reject(new Error("No Import"));
};

const patterns = await Grammar.parse(`
    use params {
        value = default-value
    }
    default-value = "DefaultValue"
    alias = value
`, { 
    resolveImport: resolver,
    params: [new Literal("value", "Value")] 
});

const result = patterns["alias"].exec("Value");
// result.ast.value will be "Value"

Key Features of Custom Resolvers

Flexibility: Load patterns from any source (filesystem, network, database, etc.)
Parameter Support: Handle parameter passing between imported patterns
Alias Support: Support pattern aliasing during import
Default Values: Provide default values for parameters
Error Handling: Custom error handling for import failures
Resource Tracking: Track the origin of imported patterns

Resolver Interface

The resolver function should implement the following interface:

type Resolver = (resource: string, originResource: string | null) => Promise<{
    expression: string;  // The pattern expression to parse
    resource: string;    // The resource identifier
}>;

Decorators

Decorators can be applied to patterns using the @ syntax:

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>"

Key Features

Patterns are defined using backticks (`)
Each pattern definition is on a new line
The patterns function returns an object with all defined patterns
Patterns can be used immediately after definition
The AST can be manipulated after parsing (e.g., removing spaces)
The exec method can take an optional second parameter to enable debug mode

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"

Not (Negative Lookahead)

import { Not, Literal, Sequence } from "clarity-pattern-parser";

const notJohn = new Not("not-john", new Literal("john", "John"));
const name = new Literal("name", "Jane");
const pattern = new Sequence("pattern", [notJohn, name]);

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

Repeat

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

const digit = new Regex("digit", "\\d+");
const comma = new Literal("comma", ",");
const digits = new Repeat("digits", digit, { divider: comma, min: 1, max: 3 });

const result = digits.exec("1,2,3");
// result.ast.value will be "1,2,3"

Take Until

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

const scriptText = new TakeUntil("script-text", new Literal("end-script", "</script"));
const result = scriptText.exec("function() { return 1; }</script>");
// result.ast.value will be "function() { return 1; }"

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"

Key Features of Direct Pattern Usage

Full control over pattern construction and configuration
Ability to create custom pattern types
Direct access to pattern execution and AST manipulation
Better performance for complex patterns
Easier debugging and testing
More flexible pattern composition

Pattern Interface

All patterns implement the Pattern interface, which provides a consistent API for pattern matching and manipulation.

Core Methods

`parse(cursor: Cursor): Node | null`

Parses the text using the provided cursor and returns a Node if successful.

cursor: The cursor tracking the current parsing position
Returns: A Node if parsing succeeds, null otherwise

`exec(text: string, record?: boolean): ParseResult`

Executes the pattern against the given text and returns a ParseResult containing the AST and any errors.

text: The text to parse
record: Optional boolean to enable debug recording
Returns: ParseResult with AST and error information

`test(text: string, record?: boolean): boolean`

Tests if the pattern matches the given text without building an AST.

text: The text to test
record: Optional boolean to enable debug recording
Returns: true if the pattern matches, false otherwise

`clone(name?: string): Pattern`

Creates a deep copy of the pattern.

name: Optional new name for the cloned pattern
Returns: A new instance of the pattern

Token Methods

`getTokens(): string[]`

Returns all possible tokens that this pattern can match.

Returns: Array of possible token strings

`getTokensAfter(childReference: Pattern): string[]`

Returns tokens that can appear after a specific child pattern.

childReference: The child pattern to check after
Returns: Array of possible token strings

`getNextTokens(): string[]`

Returns the next possible tokens based on the current state.

Returns: Array of possible token strings

Pattern Methods

`getPatterns(): Pattern[]`

Returns all child patterns.

Returns: Array of child patterns

`getPatternsAfter(childReference: Pattern): Pattern[]`

Returns patterns that can appear after a specific child pattern.

childReference: The child pattern to check after
Returns: Array of possible patterns

`getNextPatterns(): Pattern[]`

Returns the next possible patterns based on the current state.

Returns: Array of possible patterns

Utility Methods

`find(predicate: (pattern: Pattern) => boolean): Pattern | null`

Finds a pattern that matches the given predicate.

predicate: Function that tests each pattern
Returns: The first matching pattern or null

`isEqual(pattern: Pattern): boolean`

Tests if this pattern is equal to another pattern.

pattern: The pattern to compare with
Returns: true if patterns are equal, false otherwise

Properties

id: Unique identifier for the pattern
type: Type of the pattern (e.g., "literal", "regex", "sequence")
name: Name of the pattern
parent: Parent pattern or null
children: Array of child patterns
startedOnIndex: Index where pattern matching started parsing

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;
}

Node Class Reference

The Node class is the fundamental building block of the AST (Abstract Syntax Tree) in Clarity Pattern Parser. It provides a rich set of methods for tree manipulation and traversal.

Basic Properties

id: Unique identifier for the node
type: Type of the node (e.g., "literal", "regex", "sequence")
name: Name of the node
value: String value of the node (concatenated from children if present)
firstIndex: First character index in the input text
lastIndex: Last character index in the input text
startIndex: Starting position in the input text
endIndex: Ending position in the input text
parent: Parent node or null
children: Array of child nodes
hasChildren: Whether the node has any children
isLeaf: Whether the node is a leaf (no children)

Tree Manipulation

// Create nodes
const node = Node.createValueNode("type", "name", "value");
const parent = Node.createNode("type", "name", [node]);

// Add/remove children
parent.appendChild(newNode);
parent.removeChild(node);
parent.removeAllChildren();

// Insert/replace nodes
parent.insertBefore(newNode, referenceNode);
parent.replaceChild(newNode, referenceNode);
node.replaceWith(newNode);

// Navigate siblings
const next = node.nextSibling();
const prev = node.previousSibling();

Tree Traversal

// Find nodes
const found = node.find(n => n.name === "target");
const all = node.findAll(n => n.type === "literal");

// Walk the tree
node.walkUp(n => console.log(n.name));  // Bottom-up
node.walkDown(n => console.log(n.name)); // Top-down
node.walkBreadthFirst(n => console.log(n.name)); // Level by level

// Find ancestors
const ancestor = node.findAncestor(n => n.type === "parent");

Tree Transformation

// Transform nodes based on type
const transformed = node.transform({
    "literal": n => Node.createValueNode("new-type", n.name, n.value),
    "sequence": n => Node.createNode("new-type", n.name, n.children)
});

Tree Operations

// Flatten tree to array
const nodes = node.flatten();

// Compact node (remove children, keep value)
node.compact();

// Clone node
const clone = node.clone();

// Normalize indices
node.normalize();

// Convert to JSON
const json = node.toJson(2);

Static Methods

// Create a value node
const valueNode = Node.createValueNode("type", "name", "value");

// Create a node with children
const parentNode = Node.createNode("type", "name", [child1, child2]);

Keywords

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Package last updated on 05 May 2025

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clarity-pattern-parser