whenIsRight

Applies a function only when the input is an EitherRight. Otherwise, the original value is returned as-is.

Interactive example

Syntax

Classic signature

function whenIsRight<
	const GenericInput extends unknown, 
	const GenericOutput
>(
  input: GenericInput,
  theFunction: (value: Unwrap<Extract<GenericInput, EitherRight>>) => GenericOutput
): Exclude<GenericInput, EitherRight> | GenericOutput;

Curried signature

function whenIsRight<
	const GenericInput extends unknown, 
	const GenericOutput
>(
  theFunction: (value: Unwrap<Extract<GenericInput, EitherRight>>) => GenericOutput
): (input: GenericInput) => Exclude<GenericInput, EitherRight> | GenericOutput;

Parameters

• theFunction: Callback executed only on the Right part.
• input (overload 2): Value to process immediately (otherwise the returned function awaits an Either).

Return value

• Curried overload: returns a function ready to use in a pipeline.
• Direct overload: returns either the callback result (if Right) or the initial value.

Use cases

• Enrich a Right (logging, transformation) without touching Left values.
• Inject whenIsRight into pipe to keep a smooth flow.
• Replace repetitive if (E.isRight(...)) with a functional API.

See also

• isRight – Manually test the type before acting.
• whenIsLeft – Error-side counterpart.
• whenHasInformation – Pattern matching based on literal info.