npm install -g typescript-parsec

ts-parsec is a parser combinator library prepared for typescript. By using this library, you are able to create parsers very quickly using just a few lines of code. For document and more information, please checkout our repo on github, or our document page.

``typescript
import { buildLexer, expectEOF, expectSingleResult, rule, Token } from 'typescript-parsec';
import { alt, apply, kmid, lrec_sc, seq, str, tok } from 'typescript-parsec';

enum TokenKind {
Number,
Add,
Sub,
Mul,
Div,
LParen,
RParen,
Space,
}

const lexer = buildLexer([
[true, /^\d+(\.\d+)?/g, TokenKind.Number],
[true, /^\+/g, TokenKind.Add],
[true, /^\-/g, TokenKind.Sub],
[true, /^\*/g, TokenKind.Mul],
[true, /^\//g, TokenKind.Div],
[true, /^\(/g, TokenKind.LParen],
[true, /^\)/g, TokenKind.RParen],
[false, /^\s+/g, TokenKind.Space]
]);

function applyNumber(value: Token): number {
return +value.text;
}

function applyUnary(value: [Token, number]): number {
switch (value[0].text) {
case '+': return +value[1];
case '-': return -value[1];
default: throw new Error(Unknown unary operator: ${value[0].text});
}
}

function applyBinary(first: number, second: [Token, number]): number {
switch (second[0].text) {
case '+': return first + second[1];
case '-': return first - second[1];
case '': return first second[1];
case '/': return first / second[1];
default: throw new Error(Unknown binary operator: ${second[0].text});
}
}

const TERM = rule();
const FACTOR = rule();
const EXP = rule();

/*
TERM
= NUMBER
= ('+' | '-') TERM
= '(' EXP ')'
*/
TERM.setPattern(
alt(
apply(tok(TokenKind.Number), applyNumber),
apply(seq(alt(str('+'), str('-')), TERM), applyUnary),
kmid(str('('), EXP, str(')'))
)
);

/*
FACTOR
= TERM
= FACTOR ('*' | '/') TERM
*/
FACTOR.setPattern(
lrec_sc(TERM, seq(alt(str('*'), str('/')), TERM), applyBinary)
);

/*
EXP
= FACTOR
= EXP ('+' | '-') FACTOR
*/
EXP.setPattern(
lrec_sc(FACTOR, seq(alt(str('+'), str('-')), FACTOR), applyBinary)
);

function evaluate(expr: string): number {
return expectSingleResult(expectEOF(EXP.parse(lexer.parse(expr))));
}

console.log(evaluate('(1 + 2) * (3 + 4)'));
``