Detecting whether two strings are anagrams, in Haskell.

anagrams.hs

import Data.List
import Test.QuickCheck

anagrams :: String -> String -> Bool
anagrams x y = sort x == sort y

main = do
    quickCheck (\(x, y) -> length x <= 8 ==> anagrams x y == (y `elem` permutations x))
    -- tests `anagrams` using 100 sets of 2 random strings
    -- uses an obvious but painfully slow algorithm
    -- discards any test string longer than 8 characters as generating the permutations takes forever

Aren't the chances that 100 random pairs of strings contain a pair that are an anagram of each other vanishingly small?

Yeah, you could knock up the number of tries. Honestly, in a real system, I would have normal unit tests along with the QuickCheck tests. They're not great on their own, but they're brilliant at catching edge-cases. — Samir.

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On 1 Aug 2012, at 10:31, Tom Denley ***@***.*** wrote: Aren't the chances that 100 random pairs of strings contain a pair that are an anagram of each other vanishingly small? --- Reply to this email directly or view it on GitHub: https://gist.github.com/3212228

I'm aware this was posted a while ago, but here is an addition; a case-insensitive version. I'm not very experienced so I wonder if this could be more concise

module AnagramDetection where
import Data.Char(toLower)
import Data.List

isAnagramOf :: String -> String -> Bool
isAnagramOf test original = sort (lower test) == sort (lower original)

lower :: String -> String
lower "" = ""
lower (a:as) = toLower a : lower as

Your lower function could just be implemented as map toLower.

I think the tersest solution I can think of looks something like this:

import Data.Char (toLower)
import Data.Function (on)
import Data.List (sort)

...

isAnagramOf = (==) `on` (sort . map toLower)

This is the equivalent of:

isAnagramOf a b = sort (map toLower a) == sort (map toLower b)

Didn't expect such a quick response, but -- AAAAAHHHH So that's how you map a function, I tried map toLower but actually wasn't placing the parentheses properly; so my newb self just applied an extra function.

Thank you for the response and explanation!