Function oneOf

If you are parsing JSON, the values can be strings, floats, booleans, arrays, objects, or null. You need a way to pick oneOf them! Here is a sample of what that code might look like:

Example

type Json =
   | ReturnType<typeof JNumber>
   | ReturnType<typeof JBoolean>
   | typeof JNull;

const JNumber = (n: number) =>
 ({
    kind: "JNumber",
    value: n,
  } as const);

const JBoolean = (b: boolean) =>
  ({
    kind: "JBoolean",
    value: b,
  } as const);

const JNull = {
  kind: "JNull",
} as const;

const json: Parser<Json> = P.oneOf(
  P.float.map(JNumber),
  P.keyword("true").map(() => JBoolean(true)),
  P.keyword("false").map(() => JBoolean(false)),
  P.keyword("null").map(() => JNull)
);

Remark

Ignore the type signature at the top of this page. It is showing the first of several overloaded definitions. Instead, think of it as having the type signature oneOf<A>(...parsers: Parser<A>[]): Parser<A>

See

• oneOfMany like oneOf but with different type inference.