Raise a signal when using Traversal / Prism to modify data but it couldn't locate any element in array by predicate about monocle-ts HOT 1 CLOSED

I don't think you can do this and have your optics still obey the optics laws. Modify means "change what you're focused on and then give me the updated state" and if you aren't focused on something, then there's nothing to change, so it by definition cannot fail.

One of the (math-based) laws of traversals is that a modification of a traversal must result in a traversable with the same number of items. If your modify returned an error in some cases, it would violate this law. source

Put another way, how do you compose traversals if one of them can return an error but the other must take a traversable?

And because prisms are a special type of traversal, it must obey the same law.

You're misunderstanding the purpose of traversal.

from monocle-ts.