Consing lists with user-defined type in Haskell
- by user1319603
I have this type I defined myself:
data Item =
Book String String String Int -- Title, Author, Year, Qty
| Movie String String String Int -- Title, Director, Year, Qty
| CD String String String Int deriving Show -- Title, Artist, Year, Qty
I've created an empty list
all_Items = []
With the following function I am trying to insert a new book of type Item (Book) into the all_Items
addBook all_Items = do
putStrLn "Enter the title of the book"
tit <- getLine
putStrLn "Enter the author of the book"
aut <- getLine
putStrLn "Enter the year this book was published"
yr <- getLine
putStrLn "Enter quantity of copies for this item in the inventory"
qty <- getLine
Book tit aut yr (read qty::Int):all_Items
return(all_Items)
I however am receiving this error:
Couldn't match expected type `IO a0' with actual type `[a1]'
The error points to the line where I am using the consing operator to add the new book to the list. I can gather that it is a type error but I can't figure out what it is that I am doing wrong and how to fix it. Thanks in Advance!
