Composition & pipelines in Haskell

Counts words two ways, putting point-free and pointed style side by side.

-- (.) glues functions right to left; ($) applies one without parens.
module WordStats where

import Data.Char (isAlpha, toLower)

normalize :: String -> String
normalize = map toLower . filter (\c -> isAlpha c || c == ' ')

-- Point-free: the text argument is never named at all.
wordCount :: String -> Int
wordCount = length . words . normalize

-- The same pipeline written pointed, with ($) in place of nesting.
wordCountPointed :: String -> Int
wordCountPointed text = length $ words $ normalize text

longest :: String -> Int
longest = maximum . (0 :) . map length . words . normalize

How it works

normalize composes map toLower with a filter that drops punctuation.
wordCount = length . words . normalize never names its argument at all.
wordCountPointed text = length $ words $ normalize text does the same job with ($).

Keywords and builtins used here

Int
String
import
isAlpha
longest
module
normalize
toLower
where
wordCount
wordCountPointed

The run, in numbers

Lines: 18
Characters to type: 590
Tokens: 81
Three-star pace: 70 tpm

At the three-star pace of 70 tokens a minute, this run takes about 69 seconds.

Type this snippet

Step 3 of 3 in Functions, step 6 of 27 in Language basics.

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