Using TypeScript

Pegase was coded in TypeScript and ships with its own type declarations. The types of all entities, from semantic actions to failure objects, result objects, directives, plugins, etc. can directly be imported from pegase. For a list of all available types, please refer to API > Types. Furthermore, the peg tag accepts two optional generics: the first one types the value of the resulting parser, the second types the context option.

import peg, { $context, $raw, $fail } from "pegase";

type Context = Map<string, number>;

const g = peg<number, Context>`
  [a-z]+ ${() => {
    const val = $context().get($raw());
    if (!val) $fail(`Undeclared identifier "${$raw()}"`);
    else return val;
  }}
`;

// g is of type Parser<number, Context>