Power of Haskell

In: C#|Functional Programming|Haskell

27 May 2011

Learning haskell recently has really highlighted the power of the built in classes of haskell.

Compare a function in haskell to captialize the first letter in a sentence, vs c#.


import Data.Char
sentenceCase :: [Char] -> [Char]
sentenceCase [] = []
sentenceCase (x:xs) = [toUpper x] ++ map toLower xs

I think to be fair I should explain what the above function does.

  1. The first line is the type definition, states that the function will accept a list of chars (a string) and return a list of chars.
  2. The second line is a pattern match, in that if an empty string is provided then it will return an empty string.
  3. The third line is also a pattern match, however will only be accepted if the first pattern is passed over
  4. So in this case it will be run when accepting a non-empty string as it’s input parameter.
Function Description
sentenceCase The name of the function
(x:xs) The brackets are grouping the notation x:xs together so it’s evaluated as a single argument.
x:xs Is actually a special list shorthand that says for list xs, let the value x be the first element and xs be the remainder. Additionally this could be expressed as a:b:c:xs, abc representing the first 3 elements of the list and xs representing the remainder.
[] The left and right square brackets represent a list, so in this case we’re creating a new list filled with 1 character which will be uppercase.
toUpper From the Data.Char library accepts a Char and returns an upper case Char
toLower From the Data.Char library accepts a Char and returns a lower case Char
map Is a built in library function which performs a function on each individual member of a list and returns a resulting list. ie map (\x -> x * 2) [1,2,3] will return a list with the function (x * 2) applied to each of its elements [2,4,6]
++ Concatenates two lists.

So in 1 line of code you could read the above function as taking a list of characters, return the first element as uppercase and the remainder as lowercase.

Vs C#

public static string ToSentenceCase(this string original)
	return String.IsNullOrEmpty(original) 
		? original 
		: string.Format("{0}{1}", Head(original).ToUpper(), Tail(original).ToLower());
public static string Head(this string original)
	return String.IsNullOrEmpty(original) 
		? original 
		: original.First().ToString();
public static string Tail(this string original)
	return String.IsNullOrEmpty(original) 
		? original 
		: original.Substring(1, original.Length - 1);

To be fair, c# doesn’t have a Head or Tail method built in. However even using extension classes, the built in pattern matching from Haskell seems to be a far nicer solution language wise than c#.

Is there a way to refactor this c# code futher?

2 Responses to Power of Haskell


Rob Gray

May 27th, 2011 at 11:04 pm

Why would you make such a thing ? :p



May 27th, 2011 at 11:40 pm

Oh I dunno… whimsy?

I’m sure it’ll be such a popular request, that they’ll add it to the CSS specification at some point.

text-transform: sentence-case. 😀

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Justin is a Senior Software Engineer living in Brisbane. A Polyglot Developer proficient in multiple programming languages including [C#, C/C++, Java, Android, Ruby..]. He's currently taking an active interest in Teaching Kids to Code, Functional Programming, Robotics, 3D Printers, RC Quad-Copters and Augmented Reality.

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