What's the absurd function in Data.Void useful for?

Question

The absurd function in Data.Void has the following signature, where Void is the logically uninhabited type exported by that package:

Answer 1

Generally, you can use it to avoid apparently-partial pattern matches. For example, grabbing an approximation of the data type declarations from this answer:

data RuleSet a            = Known !a | Unknown String
data GoRuleChoices        = Japanese | Chinese
type LinesOfActionChoices = Void
type GoRuleSet            = RuleSet GoRuleChoices
type LinesOfActionRuleSet = RuleSet LinesOfActionChoices

Then you could use absurd like this, for example:

handleLOARules :: (String -> a) -> LinesOfActionsRuleSet -> a
handleLOARules f r = case r of
    Known   a -> absurd a
    Unknown s -> f s