parseCallable

Parses a value into a callable function. This parser combines the validateCallable protocol validator with the normalizeCallable normalizer to ensure that the input is a function that can be invoked with () without throwing a TypeError.

The parser never throws, never mutates input, and never invokes the function. It returns a structured ParseResult<(...args: unknown[]) => unknown> describing success or failure.

Signature

function parseCallable<
    T extends (...args: unknown[]) => unknown = (...args: unknown[]) => unknown
>(
    value: unknown
): ParseResult<T>

Behavior

• Accepts:
• normal functions
• async functions
• generator functions
• bound functions
• Rejects:
• ES2015 class constructors.
• Primitives.
• null and undefined.
• Objects without callable behavior.
• Functions with hostile or malformed toString implementations.
• Never invokes the function.
• Never throws and never mutates input.

Returns

• ok: true: And the original function when parsing succeeds.
• ok: false, value: null: And a list of issues when parsing fails.

Examples

parseCallable(() => 1)
// { ok: true, value: [Function], issues: [] }

class Foo {}
parseCallable(Foo)
// { ok: false, value: null, issues: ["Value is not a callable function"] }

Notes

• This parser is ideal for safely handling user-provided callbacks, hooks, handlers, and plugin interfaces.
• Pure, side-effect-free, and safe for all runtime environments.