That's nice and clean, but it leaves a thunk inside (since the field is lazy). Is there a strict version of `over` that avoids this? We could write one thus:
over' :: ALens s t a b -> (a -> b) -> s -> t
over' l f = getSolo . cloneLens l (\old -> Solo $! f old)
where
getSolo (Solo x) = x
On Tue, Dec 20, 2022 at 05:25:35PM +0100, PICCA Frederic-Emmanuel wrote:
> > Please clarify your question. Your code doesn't compile, and I can't tell
> > what it's supposed to do.
>
> replace a (Maybe a) value in a data using lens only if the new (Maybe a) is a Just
How about
over a (mb <|>)
?
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