Re: [Haskell-cafe] Getting started - help

firstly no it isnt homework. I havent run it through the compiler because I know it won't compile as I havent finished the function as you can see. I was just asking for guidance on how to understand what to do. So now I know to put the fan's into a list, which I have done. So then I can just add the fan's directly to the list of fans if the name of the film matches the desired film to be a fan of. Magnus Therning wrote:

First off, is this homework?

You really ought to start with passing your code to GHCi, or the compiler, to see whether it's accepted before sending questions to the mailing list. At least if you are interested in getting constructive replies.

On Thu, Apr 30, 2009 at 12:33 PM, applebiz89 wrote:

...

What I need to do is build a type of database. Firstly have a few questions, whether what I have done it right...and how to do something else.

This is my algebraic type for the database (correct me if its wrong)

data Film = Film String String Int String

with this as the data.

testDatabase :: [Film] testDatabase = [("Casino Royale", "Martin Campbell",2006, "Garry, Dave, Zoe")]

the last set of strings are the fans to the film. I want to be able to add a new fan, but not sure how to specifically insert it to there

If the fans is a "set of strings" why not represent them as a list of strings (`[String]`)?

...

this is what I have so far:

becomeFan :: String -> String -> [Film] -> [Film] becomeFan = do putStr "Which film are you a fan of:  "            filmTitle <- getLine            do putStr "What is your name: "            fanName <- getLine            (if filmTitle == filmName then fanName : [Film])

The type is wrong, you need to do this in the `IO` monad.

A more serious issue is that I don't understand at all what you intend this code to do. It isn't valid Haskell, but I think that instead of battling Haskell you should, at this point, go back to your algorithm. Answer the question, given your type, what steps are needed to add a fan to a single film? Then you can progress to answering, what steps are needed to add a fan to a specific film in a list of films?

/M

-- Magnus Therning (OpenPGP: 0xAB4DFBA4) magnus＠therning．org Jabber: magnus＠therning．org http://therning.org/magnus identi.ca|twitter: magthe _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

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