Turing complete baptisms

Per the actual wiki, some denominations seem to think it's a sin or heresy to do someone more than once. Which seems like what the nullification in the baptize function is supposed to capture.

Baptism is such a weird thing.

I think Haskell is such a weird thing

Could you imagine how op you could become though if baptisms stacked

The LDS (Mormons) actually do repeat it, in a sense. Their weekly sacrament is a renewal of their baptismal blessings

Although baptism probably has its roots in the Mikva, which is a ritual cleansing, that's not really the significance within Christianity. Baptism is not a washing away of sins, or impurity, but is rather a symbolic death and resurrection. The Apostle Paul, an early codifier of Christian doctrine whose letters became part of the Christian Bible wrote as follows in Romans chapter 6

Do you not know that all of us who have been baptized into Christ Jesus were baptized into his death? Therefore we have been buried with him by baptism into death, so that, just as Christ was raised from the dead by the glory of the Father, so we too might walk in newness of life.

This has the same end effect- the removal of sin and purification, but the conception is totally different.

I didn't expect the FP inquisition.

Half Life mentioned λ 💪 λ 💪 λ 💪 λ 💪 λ

This is probably an ok use for a GADT. Something like:

{-# LANGUAGE DataKinds      #-}
{-# LANGUAGE GADTs          #-}
{-# LANGUAGE KindSignatures #-}

data Bap = Baptized | Unbaptized

data Person :: Bap -> * where
   Baptize :: Person Unbaptized -> Person Baptized
   NewPerson :: Person Unbaptized

conditionalBaptize :: Person a -> Person Baptized
conditionalBaptize p =
    case p of NewPerson -> Baptize p
              Baptize _ -> p

main = return ()

It looks pretty normal to me as a professional Haskeller, though I suppose it's perhaps slightly cleaner to write it as conditionalBaptize p = fromMaybe p $ baptize p. It's largely just a matter of taste and I'd accept either version when reviewing an MR.

Edit: I just thought of another version that actually is far too clever and shouldn't be used:

conditionalBaptize = ap fromMaybe baptize, making use of the monad instance for ->. But yeah, don't do this.

There's an old joke about functional programming separating Church from state.