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You can reach the person managing the list at beginners-ow...@haskell.org When replying, please edit your Subject line so it is more specific than "Re: Contents of Beginners digest..." Today's Topics: 1. Re: Lazyness and forM_ (Marc Busqué) ---------------------------------------------------------------------- Message: 1 Date: Fri, 13 Apr 2018 15:32:27 +0200 (CEST) From: Marc Busqué <m...@lamarciana.com> To: The Haskell-Beginners Mailing List - Discussion of primarily beginner-level topics related to Haskell <beginners@haskell.org> Subject: Re: [Haskell-beginners] Lazyness and forM_ Message-ID: <alpine.LNX.2.21.1804131520060.7309@localhost> Content-Type: text/plain; charset="iso-8859-15"; Format="flowed" On Fri, 13 Apr 2018, Kim-Ee Yeoh wrote: > Well, > > forM_ (categories, expenses) $ withDB . createTable > > is equivalent to > > withDB . createTable $ expenses. > > So exactly one table is created. Oops, you are right. > ``` > ["a", "b"] `forM_` print > ``` > > Actually prints both `"a"` and `"b"`. > > > Here the code uses square brackets--and so we have honest-to-goodness > lists--whereas the previous used parentheses. > > See what happens with: ("a","b") `forM_` print. Now I feel embarrassed I overlooked that :) I used a tuple instead of a list because in selda `Table` are type-safe. So `categories` and `expenses` are different types and they can't go in the same list. So I guess, once the `forM_` mistery is gone, I can boil down my problem to something very different. As it has nothing to do with the current subject, I'll submit another question. > Marc: Feel free to write to the haskell-cafe mailing list for questions such > as this. Fortuitously in this case, it turns out that your query > needed knowledge only about the forM* combinators and--ever since their ilk > was generalized--the known instances declared for the Traversable > constraint. As you explore the domain-specific package "selda" further, you > will find more people acquainted with the package over at the cafe > than here in beginners. Suffice to say, everyone here in this list is also in > cafe, which is also open to beginners questions. And following your recommendation I'll submit that question in the haskell-cafe mailing list :) Thank you very much for your help :) Marc Busqué http://waiting-for-dev.github.io/about/ ------------------------------ Subject: Digest Footer _______________________________________________ Beginners mailing list Beginners@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners ------------------------------ End of Beginners Digest, Vol 118, Issue 9 *****************************************