[Haskell-cafe] handling NULL value in database query with Maybe (or other ...)

[Tom Ellis]

That is using Maybe and is not a null pointer!

Just and Nothing are the constructors of Maybe.

On Tue, Dec 18, 2018 at 03:43:35PM +0100, Damien Mattei wrote:
> thank you Tom, it is the kind of answer that help me
> i insert this and it is ok now:
> forM_ bd_rows_WDS $ \(Only x) ->
>       case x of
>         Nothing -> putStrLn ("x =" ++ "NULL")
>         Just x -> putStrLn $ ("x =" ++ Text.unpack x)
> i had seen a such solution on web but thought the Maybe was the
> solution, i hoped asked could avoid using sort of Null pointer as
> mentioned in this article:
> https://www.lucidchart.com/techblog/2015/08/31/the-worst-mistake-of-computer-science/
> if someone else have a simpler solution email me
> 
> 
> Le 18/12/2018 13:34, tom.stejskal a écrit :
> > case x of
> >     Nothing -> putStrLn "NULL"
> >     Just y -> putStrLn $ Text.unpack y