haskell - What does [safe] marker mean in ghci? -

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prelude data.void> :info void data void       -- defined in `data.void' instance [safe] eq void -- defined in `data.void' instance [safe] ord void -- defined in `data.void' instance [safe] read void -- defined in `data.void' instance [safe] show void -- defined in `data.void'

what [safe] mean?

it means datatype defined in module defined using safe extension. can find details of extension in user guide.

in fact, can test defining module using safe extension:

{-#language safe#-}  data test = test deriving (eq, show)

and trying out in ghci:

λ> :i test data test = test     instance [safe] eq test  instance [safe] show test

but note in current ghc (7.10.2), safe extension cannot relied of trust guarantee because of this ghc bug.


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