My problems are :
1. type Person = String
type Book = String
type Database = [(Person,Book)]
exampleBase
= [("Alice", "Postmn Pat"),("Anna","All Alone"),("Alice","Spot")]
books :: Database -> Person -> [Book]
borrowers :: Database -> Book -> [Person]
borrowed :: Database -> Book -> [Bool]
numBorrowed :: Database -> Person -> Int
books :: Database -> Person -> [Book]
books [] borrowers = []
books ((pers,bk):rest) borrowers
| pers == borrowers = bk : books rest borrower
| otherwise = books rest borrower
{-output :
books exampleBase "Alice" = ["Postman Pat","Spot"]
-}
borrowers :: Database -> Book -> [Person]
borrowers [] books = []
borrowers ((pers,bk):rest) books
| bk == books = pers : borrowers rest books
| otherwise = borrowers rest books
{- output:
books exampleBase "Spot" = ["Alice"]
-}
How should I do to make borrowed and numBorrowed, because it's use
String and integer, and i confuse.
2. type Name = String
type Price = Int
type BarCode = Int
type Database = [(BarCode,Name,Price)]
codeIndex :: Database
codeIndex = [(4719, "Fish Fingers",121),
(5643,"NAppies",1010),
(3814,"Orange Jelly",56)]
type TillType = [BarCode]
type BillType = [(Name,Price)]
How should I do to make function ?
- makeBill :: TillType -> BillType
- formatBill :: BillType -> String
- printBill :: TillType -> String
How should I defined BarCode to print (Name, Price)?
Thank's for your helping
