Re: [Haskell-cafe] (SPAM 3)Re: handling NULL value in database query with Maybe (or other ...)

i had many answers, i can not answer to all,first thanks just afew words, i did not want to have a C beahvior at all,i try to escape from the C world... (the solution with Just and Nothing help a lot) i espected something like that too, the answer have been given to me in comp.lang.haskell: bd_rows_WDS :: [Maybe Text] <- query conn qry_head_WDS (Only (name::String)) but it fails to compile: *Main> :load UpdateSidonie [1 of 1] Compiling Main ( UpdateSidonie.hs, interpreted ) UpdateSidonie.hs:213:5: error: Illegal type signature: ‘[Maybe Text]’ Type signatures are only allowed in patterns with ScopedTypeVariables | 213 | bd_rows_WDS :: [Maybe Text] <- query conn qry_head_WDS (Only (name::String)) | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Failed, no modules loaded. and i completely agree that Haskell is more safe than C/C++ even if as quoted here: https://esham.io/ it requires ,to do basic things " a Ph.D. and three Monoid instances "... quoted from "But zsh in particular lets you write text manipulation one-liners which in Haskell would require a Ph.D. and three Monoid instances. " :-) Le 18/12/2018 20:06, Michael Walker a écrit :

On Tue, 18 Dec 2018 at 15:34, Damien Mattei wrote:

...

ok well i do not want to open a discussion here, but i do not see any benefit in Haskell using Nothing and Just compared to other language, it's the same than if i had written in C something like : if (x == NULL) printf("NULL\n"); else printf("%s",*x);

i expected more from Haskell...

Well, you have to remember to do that in C, but in Haskell the compiler won't let you use a "Maybe a" as an "a". They're totally different things.

That seems a pretty huge benefit to me, even ignoring everything else. What more could you want?

-- Damien.Mattei@unice.fr, Damien.Mattei@oca.eu, UNS / OCA / CNRS