CODEWITHSUNDEEP
haskell
Roy
Roy

Reputation: 75

Printing the values inside a tuple in Haskell

I have a list of tuples. For example: [("A",100,1),("B",101,2)]. I need to display it in a simple way. For example: "your name is: A", "Your id is: 100".

If anyone can find a solution for this, it would be a great help. Thanks in advance.

Upvotes: 2

Views: 7714

Answers (4)

Ahmad Ismail
Ahmad Ismail

Reputation: 13872

Please try:

get1st (a,_,_) = a
get2nd (_,a,_) = a
get3rd (_,_,a) = a

showTuples [] = ""
showTuples (x:xs) = "Your name is:" ++ show(get1st(x)) ++ " Your ID is: " ++ show(get2nd(x)) ++ "\n" ++ showTuples xs

main = do
    let x = [("A",100,1),("B",101,2)]
    putStrLn . showTuples $ x

Upvotes: 0

Pratik Deoghare
Pratik Deoghare

Reputation: 37172

Quick and dirty solution 

f (x,y,z) = "your id is " ++ (show y) ++ ", your name is " ++ (show x) ++ "\n"

main = putStrLn $ foldr (++) "" (map f [("A",100,1),("B",101,2)])

OR (by @maksenov)

main = putStrLn $ concatMap f [("A",100,1),("B",101,2)]

Upvotes: 1

Nicolas Wu
Nicolas Wu

Reputation: 4985

The easiest way to do this is to create a function that works for one of the elements in your list. So you'll need something like:

showDetails :: (String, Int, Int) -> String
showDetails (name, uid, _) = "Your name is:" ++ name ++ " Your ID is: " ++ show uid

Then you would apply this function to each element in the list, which means you want to use the mapping function:

map :: (a -> b) -> [a] -> [b]

So, if your list is called xs, you would want something like:

map showDetails xs

This obviously gives you a result of type [String], so you might be interested in the unlines function:

unlines :: [String] -> String

This simply takes a list of strings, and creates a string where each element is separated by a new line.

Putting this all together, then, gives you:

main :: IO ()
main = putStrLn . unlines . map showDetails $ [("A",100,1),("B",101,2)]

Upvotes: 6

Cat Plus Plus
Cat Plus Plus

Reputation: 129894

For a single tuple, just pattern match all the elements, and do something with them. Having a function that does that, you can use map to transform the entire list.

import Data.List (foldl')

show_tuple :: (Num a, Num b) => (String, a, b) -> String
show_tuple (name, id, something) =
    "Your name is:   " ++ name ++ "\n" ++
    "Your ID is:     " ++ (show id) ++ "\n" ++
    "Your something: " ++ (show something) ++ "\n\n"

-- transforms the list, and then concatenates it into a single string
show_tuple_list :: (Num a, Num b) => [(String, a, b)] -> String
show_tuple_list = (foldl' (++) "") . (map show_tuple)

The output:

*Main Data.List> putStr $ show_tuple_list [("ab", 2, 3), ("cd", 4, 5)]
Your name is:   ab
Your ID is:     2
Your something: 3

Your name is:   cd
Your ID is:     4
Your something: 5

Upvotes: 1

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