Parsect : Parser Combinator for JavaScript/TypeScript

Abstract

Parsect is a parser combinator library for TypeScript or JavaScript. It provides a easy way to write a readable parser in only TypeScript/JavaScript without any other domain-specific languages like yacc/lex, ANTLR or PEG.js. Parsect can be used from not only TypeScript and JavaScript but also other AltJSs.

I got the idea for Parsect from Parsec parser combinator library in Haskell, however this is not a porting of Parsec. Unfortunately, this library doesn't have underlying Monad or Fanctor and it doesn't deal a string as a list of character. However, you can combine parsers in the same manner as Parsec with Parsect.

• Parsec-like API
• Statically typed: The API of Parsect is statically typed like Parsec with TypeScript. However, you can also use it from JavaScript as dynamically typed API.
• do-notation like syntax: Parsect has Haskell's do-notation-like notation style. This notation makes a parser more readable.
• Functional Programming API: Most of functions are referential transparent. It means you don't need to consider states of your parsers.
• Easy debugging: You can set a breakpoint in the middle of your parser and watch that the parser consumes the input step-by-step.　
• Exitra parsers: Regular expression parser also is supported. You can combine RegExp parsers with other parsers.
• Token parser builder: makeTokenParser function is supported.
• Expression parser builder: buildExpressionParser function is supported.

Getting Started

ES module for Browsers and Deno

import { Parsect } from "https://code4fukui.github.io/Parsect/Parsect.js";

string Parser Constructor

Parsect has some functions that creates a parser. string function is one of them. string take a string and return new parser. This parser parses the string and return it as a raw result value. For example, if you want to parse a string "apple", use string function as follows:

var parser: Parsect.Parser<string> = Parsect.string("apple");
var state: Parsect.State<void> = Parsect.state("apple, grape, banana", 0);
var reply: Parsect.Reply<string,void> = Parsect.parse(parser, state);
console.log(reply.value);   // prints "apple".

Note a difference from string in Parsec. If the parser recieve a unexpected input string like "application", the parser would consume no characters and fail. The both two words have first four letter "appl" but the parser don't throw a exception and parsing would continue to search other matchings.

many Parser Combinator

Combinator is a function takes parsers as a parameter and returns new parser. many combinator create a parser parses infinitely repeat of a string pattern. many function takes a parser and return new parser. For example, the following parser comsumes a string like "abcabcabcabc...":

Parsect.many(Parsect.string("abc"))

seq Parser Combinator

seq combinator provides do notaion like notaion for Parsect. seq function take a other function for parameter. The parameter function is called back when the seq parses a string. The parameter function recieves a other function as a parameter. Typically, seq function is used as:

var parser: Parsect.Parser<number> = Parsect.seq((s: Parsect.Context<void>): number => {
    s(string("("));
    var v: number = s(number);
    s(string(")"));
    return v;
});

This parser parses a numeric string between parenses. The argument s is a function takes a parser and execute it. A return value of s(number) is not a Parsect.State object but a raw value of result of parsing. So, the variable v would be bounded a string object. When p parses a string "(100)", v is 100.

If a parser applied to s failed, all following parsers would be ignore.

When the parsing succeeded, seq returns a State object contains the value returned from the parameter function. Otherwise, the value property of the state object is undefined, regardless of the parameter function returns any value.

If calculation for the result value is costly, you should call success() function and avoid the calculation as follows:

var parser: Parsect.Parser<number> = Parsect.seq((s: Parsect.Context<void>)=>{
    s(string("("));
    var v: number = s(number);
    s(string(")"));
    return s.success && very_very_large_operation(v);
});

or combinator

or combinator takes some parsers as parameter and try parsing in sequence. If one of them could parse the input, the State object would be returned. For example, the following parser will consume any combination of "a" or "b":

Parsect.many(Parsect.or(Parsect.string("a"), Parsect.string("b")));

Common Pitfall

Left Recursion

(TODO: Left Recursion)

Definition Ordering and lazy parser

(TODO: Definition Ordering)

Predictive Parsers

Here are two parsers. pa parses "[a]" and pb parses "[b]". A parser or(pa, pb) fails to parse "[b]".

var pa = Parsect.between(Parsect.string('['), Parsect.string('a'), Parsect.string(']'));
var pb = Parsect.between(Parsect.string('['), Parsect.string('b'), Parsect.string(']'));
var parser = Parsect.or(pa, pb);

var state = Parsect.state("(b)", 0);
var reply = Parsect.parse(parser, state);
console.log(reply.success);                 // prints "false"!

It's because pa consumes "[" even if whole of pa failed. Generally, commonalizing "[" of both of parsers is the best way.

var pa = Parsect.series(Parsect.string('a'), Parsect.string(']'));
var pb = Parsect.series(Parsect.string('b'), Parsect.string(']'));
var parser  = Parsect.seq(s=>{
    s(string('['));
    return s(Parsect.or(pa, pb));
});

var state = Parsect.state("(b)", 0);
var reply = Parsect.parse(parser, state);
console.log(reply.success);                 // prints "true"!

However, if commonalizing is difficult, you can use triable combinator to solve it. triable parser can retrieve overconsumed strings.

var pa = Parsect.between(Parsect.string('['), Parsect.string('a'), Parsect.string(']'));
var pb = Parsect.between(Parsect.string('['), Parsect.string('b'), Parsect.string(']'));
var parser = Parsect.or(Parsect.triable(pa), pb);

var state = Parsect.state("(b)", 0);
var reply = Parsect.parse(parser, state);
console.log(reply.success);                 // prints "true"!

APIs

Date Types

---

class State

Type Variables

• U User state.

Constructors

• state(source: string, position: number = 0, userState?: U): State<U>

Members

• source: string Source string.
• position: number Current position.
• getRowColumn(): { raw: number; column: number; } Calculate raw number and column number from current position. Those values are ZERO-BASED.
• seek(delta: number): State<U> Creates new State object that has new position.
• equals(src: State<U>): boolean Compare two state objects.

---

class Reply

class Reply<A,U>

Type Variables

• A Semantic value.
• U User state.

Constructors

• ok<A,U>(state: State<U>, value: A): Reply<A,U>
• error<A,U>(state: State<U>, expected?: ()=> string): Reply<A,U>

Members

• state: State<U> State after the parsing.
• success: boolean Succeed or failed.
• value: A The semantic value.
• expected: ()=> string
• equals(st: Reply<A,U>): boolean

---

interface Context

Type Variables

• U User state.

Members

• <T>(p: Parser<T>): T
• userState: U (read/write) Current user state.
• peek: string (For debugging) Current input string.
• success: boolean (For debugging) Success or fail.

---

parse<A,U>(parser: Parser<A>, state: State<U>): Reply<A,U>

Invoke parser with the state.

// parser parses "abc" between "[" and "]".
var parser: Parsect.State<string> = Parsect.between(
    Parsect.string("["),
    Parsect.string("abc"),
    Parsect.string("]")
);

var state: Parsect.State<void> = Parsect.state("[abc]", 0);
var reply: Reply<void> = Parsect.parse(parser, state);
console.log(reply.success);             // true
console.log(reply.value);               // "abc"
console.log(reply.state.source);        // "[abc]"
console.log(reply.state.position);      // 5

var state2: Parsect.State<void> = Parsect.state("[xyz]", 0);
var reply2: Reply<void> = Parsect.parse(parser, state);
console.log(reply2.success);             // false
console.log(reply2.expected);            // "abc"
console.log(reply2.state.source);        // "[abc]"
console.log(reply2.state.position);      // 1    (It's because the parser consume heading "[" then failed)

---

Parser Constructors

---

choice<T>(ps: Parser<T>[]): Parser<T>

or<T>(...ps: Parser<T>[]): Parser<T>

repeat<T>(min: number, max: number, p: Parser<T>): Parser<T[]>

count<T>(n: number, p: Parser<T>): Parser<T[]>

many<T>(p:Parser<T>): Parser<T[]>

many1<T>(p: Parser<T>): Parser<T[]>

array<T>(ps: Parser<T>[]): Parser<T[]>

series<T>(...ps: Parser<T>[]): Parser<T[]>

head<T>(p:Parser<T>, ...ps:Parser<any>[]): Parser<T>

between<T>(open:Parser<any>, p:Parser<T>, close:Parser<any>): Parser<T>

seq<A,U>(f: (s: Context<A,U>)=>A): Parser<A>

sepByN<A>(min: number, max: number, p: Parser<A>, sep: Parser<any>): Parser<A[]>

sepBy1<T>(p: Parser<T>, sep: Parser<any>): Parser<T[]>

sepBy<T>(p:Parser<T>, sep:Parser<any>): Parser<T[]>

endByN<T>(min: number, max: number, p: Parser<T>, sep: Parser<any>): Parser<T[]>

endBy1<T>(p: Parser<T>, sep: Parser<any>): Parser<T[]>

endBy<T>(p: Parser<T>, sep: Parser<any>): Parser<T[]>

option<T>(defaultValue: T, p: Parser<T>): Parser<T>

optional<T>(p: Parser<T>): Parser<void>

skipMany<A>(p: Parser<A>): Parser<void>

skipMany1<A>(p: Parser<A>): Parser<void>

Error Handling Parser Constructors

fail(message: string): Parser<any>

unexpected(message: string): Parser<any>

Primitive Parsers

eof: Parser<void>

empty: Parser<void>

label<A>(message: string, p: Parser<A>): Parser<A>

lookAhead<T>(p: Parser<T>): Parser<T>

pure<A>(x: A): Parser<A>

triable<A>(p: Parser<A>): Parser<A>

notFollowedBy<A>(p: Parser<A>): Parser<void>

fmap<A,B>(f: (x: A)=>B, p: Parser<A>): Parser<B>

lazy<A>(f: () => Parser<A>): Parser<A>

character Parsers

oneOf(chars: string): Parser<string>

noneOf(chars: string): Parser<string>

space: Parser<string>

spaces: Parser<string>

newline: Parser<string>

tab: Parser<string>

upper: Parser<string>

lower: Parser<string>

alphaNum: Parser<string>

letter: Parser<string>

digit: Parser<string>

hexDigit: Parser<string>

octDigit: Parser<string>

char(c: string): Parser<string>

anyChar: Parser<string>

satisfy(condition: (character: string, code: number)=>boolean): Parser<string>

charCode(charCode: number): Parser<string>

---

String Parsers

---

string(text: string, caseSensitive: boolean = true): Parser<string>

regexp(pattern: RegExp): Parser<string>

---

Token Parser

---

interface LanguageDef

• commentStart: Parser<string>
• commentEnd: Parser<string>
• commentLine: Parser<string>
• nestedComments: boolean
• identStart: Parser<string>
• identLetter: Parser<string>
• opStart: Parser<string>
• opLetter: Parser<string>
• reservedNames: string[]
• reservedOpNames: string[]
• caseSensitive: boolean

interface GenTokenParser

• identifier: Parser<string>

• reserved: (s: string)=>Parser<string>

• operator: Parser<string>

• reservedOp: (s: string)=>Parser<string>

• charLiteral: Parser<string>

• stringLiteral: Parser<string>

• natural: Parser<number>

• integer: Parser<number>

• float: Parser<number>

• naturalOrFloat: Parser<number>

• decimal: Parser<number>

• hexadecimal: Parser<number>

• octal: Parser<number>

• symbol: (s: String)=>Parser<string>

• lexeme: <A>(p: Parser<A>)=>Parser<A>

• whiteSpace: Parser<void>

• parens: <A>(p: Parser<A>)=>Parser<A>

• braces: <A>(p: Parser<A>)=>Parser<A>

• angles: <A>(p: Parser<A>)=>Parser<A>

• brackets: <A>(p: Parser<A>)=>Parser<A>

• semi: Parser<string>

• comma: Parser<string>

• colon: Parser<string>

• dot: Parser<string>

• semiSep: <A>(p: Parser<A>)=>Parser<A[]>

• semiSep1: <A>(p: Parser<A>)=>Parser<A[]>

• commaSep: <A>(p: Parser<A>)=>Parser<A[]>

• commaSep1: <A>(p: Parser<A>)=>Parser<A[]>

• binary: <A>(name: string, fun: (a: A, b: A)=>A, assoc: Assoc) => Operator<A>

• prefix: <A>(name: string, fun: (a: A)=>A) => Operator<A>

• postfix: <A>(name: string, fun: (a: A)=>A) => Operator<A>

makeTokenParser(def: LanguageDef): GenTokenParser

---

Expression Parser

---

enum Assoc

• None
• Left
• Right

infix<A>(p: Parser<(l: A, r: A) => A>, assoc: Assoc): Operator<A>

prefix<A>(p: Parser<(a: A) => A>): Operator<A>

postfix<A>(p: Parser<(a: A) => A>): Operator<A>

buildExpressionParser<A>(table: Operator<A>[][], term: Parser<A>): Parser<A>

Change log

• 2013/09/26 ver. 0.2. All APIs are cleaned up. makeTokenParser and buildExpressionParser supported.
• 2013/01/01 ver. 0.1. Happy New Year!

TODO

• Adding more test cases or examples.
• Performance tuning.
• Cleaning up user state API.

License

Parsect is licensed under the MIT License.

The MIT License

Copyright 2013 Kon (http://phyzkit.net/)

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.

Some of the codes of Parsect were ported from Parsec. Parsec is provided under BSD-style license as below:

Copyright 1999-2000, Daan Leijen; 2007, Paolo Martini. All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are met:

* Redistributions of source code must retain the above copyright notice,
  this list of conditions and the following disclaimer.
* Redistributions in binary form must reproduce the above copyright
  notice, this list of conditions and the following disclaimer in the
  documentation and/or other materials provided with the distribution.

This software is provided by the copyright holders "as is" and any express or
implied warranties, including, but not limited to, the implied warranties of
merchantability and fitness for a particular purpose are disclaimed. In no
event shall the copyright holders be liable for any direct, indirect,
incidental, special, exemplary, or consequential damages (including, but not
limited to, procurement of substitute goods or services; loss of use, data,
or profits; or business interruption) however caused and on any theory of
liability, whether in contract, strict liability, or tort (including
negligence or otherwise) arising in any way out of the use of this software,
even if advised of the possibility of such damage.    

Projects

• BanchaScript is a AltJS, a programming language compiled into JavaScript source code.

Contact

Author: Kon ( @KDKTN, http://phyzkit.net/ )

日本語でもおｋ Japanese also available to contact me.