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mniip
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Jan 23, 2026
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| maybeThese :: Maybe a -> Maybe b -> Maybe (These a b) | ||
| maybeThese (Just x) (Just y) = Just (These x y) | ||
| maybeThese (Just x) Nothing = Just (This x) | ||
| maybeThese Nothing (Just y) = Just (That y) | ||
| maybeThese Nothing Nothing = Nothing |
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This adds an function realising an important property of
These. I've found the function useful in practice: for example, it allows one to make data structures containingTheseviamapMaybe. The reverse isomorphism is not really required, since it has coordinatesjustHereandjustThere, which already exist.I'd be happy putting it in
Data.These.Combinatorsinstead; to me it seems just as comfortable in the main file; the division is not very clear-cut.