Haskell 2e : Tuples

Haskell 2e : Tuples In some ways, tuples are like lists — they are a way to store several values into a single value. However, there are a few fundamental differences. A list of numbers is a list of numbers. That's its type and it doesn't matter if it has only one number in it or an infinite amount of numbers. Tuples, however, are used when you know exactly how many values you want to combine and its type depends on how many components it has and the types of the components. They are denoted with parentheses and their components are separated by commas. Another key difference is that they don't have to be homogenous. Unlike a list, a tuple can contain a combination of several types. Think about how we'd represent a two-dimensional vector in Haskell. One way would be to use a list. That would kind of work. So what if we wanted to put a couple of vectors in a list to represent points of a shape on a two-dimensional plane? We could do something like [[1,2],[8,11],[4,5]]. The problem with that method is that we could also do stuff like [[1,2],[8,11,5],[4,5]], fst takes a pair and returns its first component. ghci＞ fst (8,11) 8 ghci＞ fst ("Wow", False) "Wow" snd takes a pair and returns its second component. Surprise! ghci＞ snd (8,11) 11 ghci＞ snd ("Wow", False) False Note: these functions operate only on pairs. They won't work on triples, 4-tuples, 5-tuples, etc. We'll go over extracting data from tuples in different ways a bit later. A cool function that produces a list of pairs: zip. It takes two lists and then zips them together into one list by joining the matching elements into pairs. It's a really simple function but it has loads of uses. It's especially useful for when you want to combine two lists in a way or traverse two lists simultaneously. Here's a demonstration. ghci＞ zip [1,2,3,4,5] [5,5,5,5,5] [(1,5),(2,5),(3,5),(4,5),(5,5)] ghci＞ zip [1 .. 5] ["one", "two", "three", "four", "five"] [(1,"one"),(2,"two"),(3,"three"),(4,"four"),(5,"five")]