[Haskell-beginners] How to include {-# LANGUAGE LambdaCase #-} at the ghci prompt

[amindfv at mailbox.org]

On Fri, Mar 26, 2021 at 06:31:53PM +0100, Francesco Ariis wrote:
> Il 26 marzo 2021 alle 12:20 Galaxy Being ha scritto:
> > I've got this code I've entered into the ghci by hand between :{ and :}
> > 
> > :{
> > {-# LANGUAGE LambdaCase #-}
> > data List a = Empty | Cons a (List a) deriving (Eq, Ord, Show)
> > infixr 5 `Cons`
> > 
> > subst_c :: (a -> Bool)  -> (a, MyList a) -> MyList a
> > subst_c pred = \ case
> >                      (_, Empty)    -> Empty
> >                      (n, Cons e t)
> >                        | pred e    -> Cons n $ subst_c pred (n, t)
> >                        | otherwise -> Cons e $ subst_c pred (n, t)
> > :}
> > 
> 
>     λ> :set -XLambdaCase

You can also start GHCi with it:

    $ ghci -XLambdaCase

Tom