How to resolve the algorithm Greatest element of a list step by step in the Haskell programming language
How to resolve the algorithm Greatest element of a list step by step in the Haskell programming language
Table of Contents
Problem Statement
Create a function that returns the maximum value in a provided set of values, where the number of values may not be known until run-time.
Let's start with the solution:
Step by Step solution about How to resolve the algorithm Greatest element of a list step by step in the Haskell programming language
The provided Haskell code defines a function my_max
twice, using two different approaches to calculate the maximum value from a list. Let's break down the code:
-
First Definition of
my_max
:my_max = maximum
This definition simply reassigns the
my_max
function to the built-inmaximum
function provided by the standard library.maximum
takes a list as input and returns the maximum element in the list. -
Second Definition of
my_max
:my_max = foldl1 max
This definition uses the
foldl1
function to calculate the maximum value.foldl1
is a higher-order function that applies a binary function (in this case,max
) to a list, starting from the leftmost element and recursively combining them. Themax
function returns the larger of its two arguments. -
Using
maximumBy
:import Data.List (maximumBy) import Data.Ord (comparing) wds :: [String] wds = ["alpha", "beta", "gamma", "delta", "epsilon", "zeta"] main :: IO () main = print $ maximumBy (comparing length) wds
In this section of code:
-
The
maximumBy
function is imported from theData.List
module.maximumBy
takes two arguments: a comparison function and a list. It returns the element from the list that satisfies the comparison function. -
A string list
wds
is defined with several Greek alphabet letters. -
The
main
function prints the result of applyingmaximumBy
to the listwds
. The comparison function used iscomparing length
, which compares the lengths of the strings in the list.
-
-
Definition of
maximumBy
:maximumBy :: Foldable t => (a -> a -> Ordering) -> t a -> a maximumBy cmp = let max_ x y = case cmp x y of GT -> x _ -> y in foldr1 max_
This is the full definition of the
maximumBy
function that was imported earlier. It takes two type parameters:t
(the foldable data type) anda
(the element type). It also takes a comparison functioncmp
that takes two elements of typea
and returns anOrdering
value.The
maximumBy
function uses a helper functionmax_
to compare two elements.max_
returns the first element if the comparison function returnsGT
(greater than), and the second element otherwise.The
foldr1
function is used to fold the list of elements using themax_
function.foldr1
applies the binary function (in this case,max_
) to each element in the list, starting from the rightmost element and recursively combining them.
Source code in the haskell programming language
my_max = maximum
my_max = foldl1 max
import Data.List (maximumBy)
import Data.Ord (comparing)
wds :: [String]
wds = ["alpha", "beta", "gamma", "delta", "epsilon", "zeta"]
main :: IO ()
main = print $ maximumBy (comparing length) wds
maximumBy
:: Foldable t
=> (a -> a -> Ordering) -> t a -> a
maximumBy cmp =
let max_ x y =
case cmp x y of
GT -> x
_ -> y
in foldr1 max_
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