Summary-Haskell-3] Haskell Common Data Structures

Haskell Common Data Structure Table of Contents

• 1. Haskell basic knowledge
• 2 Haskell important data structure-list
• 3 Haskell Common Data Structures
  • 3.1 What is tuple?
  • 3.2 pair
    • 3.2.1 what is pair?
    • 3.2.2 pair-related functions
  • 3.3 Use tuple to write programs

1 Haskell basic knowledge 2 Haskell important data structure-list3 Haskell Common Data Structure 3.1 What is tuple

Tuple is a binary group, triple, etc. The elements in the group can be of different types, and the list element must be of the same type.

ghci>(1,2)(1,2)ghci>('h','i','j')('h','i','j')ghci>(1,'a',3.5)(1,'a',3.5)

The following example shows that the element types in the tuple determine the tuple type, that is, () and ('A', 'B') are both binary groups, but not the same type (1, 2) and (1, 2, 3) Although the element type is the same, but the number is different, it is not the same type

ghci>[(1,2),(3,4),(5,6)][(1,2),(3,4),(5,6)]ghci>[(1,2),('a','b')]errorghci>[(1,2),(3,4,5)]error

3.2 What is pair3.2.1

Pair is a binary group.

ghci>(1,2)(1,2)ghci>(3,4)(3,4)

3.2.2 pair-related functions

• FST/SND

ghci>fst (2,3)2ghci>snd (2,3)3

• Zip

ghci>zip [1,2,3] ['a','b','c'][(1,'a'),(2,'b'),(3,'c')]

ghci>zip [1..] ["Apple","Moto","Nokia"][(1,"Apple"),(2,"Moto"),(3,"Nokia")]

3.3 Use tuple to write programs

Example 1 Constraint Programming: Find All right triangles with three sides within [1, 10]

ghci>[(a,b,c) | a <- [1..10], b <- [1..a], c <- [1..b], b^2 + c^2 == a^2][(5,4,3),(10,8,6)]

Example 2 tuple and pattern matching

first (x,_,_) = xsecond (_,y,_) = ythird (_,_,z) = z

ghci>first ('a',3,6.7)'a'ghci>second ('a',3,6.7)3ghci>third ('a',3,6.7)6.7

Example 3

sumPair xs = [x + y| (x,y) <- xs ]

ghci>sumPair [(1,2),(3,4),(5,6)][3,7,11]

sumPair' xs = [z | (x,y) <- xs, let z = x + y]

Note: cannot be directly written as Z = x + y

ghci>sumPair' [(1,2),(3,4),(5,6)][3,7,11]

Example 4

zip' _ [] = []zip' [] _ = []zip' (x:xs) (y:ys) = (x,y):zip' xs ys

ghci>zip' [1..] ["Apple","***","MI"][(1,"Apple"),(2,"***"),(3,"MI")]