Function isLeft

isLeft<R, L>(either: Either<R, L>): either is Left<never, L>
Standalone type guard for 'left'

Useful for passing as a predicate to collection transformers
Type Parameters
- R
  underlying value type
- L
  underlying error type
Parameters
- either: Either<R, L>
  Either instance
Returns either is Left<never, L>
'true' in case argument is 'left error' (and resolves type to be 'left')
- Defined in either.ts:611