[Haskell-cafe] Re: Silly question: accessing a slot in a data type

Fernando Rodriguez wrote:

Hi,

I'm writing a very simple address book. I defined the follwoing types for Contact and AddressBook:

type Name= String type PhoneNumber= Integer

data Contact = Contact {name :: Name, phone:: PhoneNumber} deriving Show

-- The addressBook is a lista of Contacts data AddressBook= AddressBook [Contact] deriving Show

-- Create a test one ag = Agenda [Contact "BillG" 618965332, Contact "Linus" 5897458]

I wan't to write a function to search for a given phone by name and return a Maybe PhoneNumber. I know how to do this recursively on a "raw" list, but how do I access the list inside AddressBook? Also, how do I represent an AddressBook with an empty list and one with data on its list for my pattern matching?

Thanks!

Sorry, I meant to write something along the lines of bookHead :: AddressBook -> Contact bookHead (AddressBook (c:cs)) = c which isn't really useful. I think you want to say type AdressBook = [Contact] instead. -- (c) this sig last receiving data processing entity. Inspect headers for past copyright information. All rights reserved. Unauthorised copying, hiring, renting, public performance and/or broadcasting of this signature prohibited.