Discussion on: Write a script to identify an anagram

[Kasey Speakman]

Edit: Added sort-based solution for Elm.

import String
import List

sortLetters word =
  List.sort (String.toList word)

isAnagram word1 word2 =
  sortLetters word1 == sortLetters word2

---

I think the primes thing was actually harder than what I did. Here is my 15-line Elm solution where you could also reuse the breakdown of how many of which letters were used. I could have turned it into 1 long line with the 3 import statements, but I won't do that to you. :)

Read this code from the bottom up. I got used to writing it like this in F# because of its single-pass compiler. This is not a requirement of Elm, though.

import Dict exposing (Dict)
import String
import Char


updateCount countM =
  case countM of
    -- no previous count of letter, set to 1
    Nothing ->
      Just 1

    -- saw same letter again, increment
    Just i ->
      Just (i + 1)

updateAnalysis char dict =
  Dict.update (Char.toLower char) updateCount dict

analyzeWord word =
  String.foldr updateAnalysis Dict.empty word

isAnagram word1 word2 =
  -- built-in equality superpowers
  analyzeWord word1 == analyzeWord word2

Don't take my word for it.

Here is a full program with tests that you can run over at elm-lang.org/try. Paste the code below in the left window and hit the Compile button.

I included type annotations for clarity, but they are not necessary.

import Html exposing (Html, text, div, span, u)
import Html.Attributes exposing (style)
import Dict exposing (Dict)
import String
import Char


-- anagram functions

type alias WordAnalysis = Dict Char Int

updateCount : Maybe Int -> Maybe Int
updateCount countM =
  case countM of
    -- no previous count of letter, set to 1
    Nothing ->
      Just 1

    -- saw same letter again, increment
    Just i ->
      Just (i + 1)

updateAnalysis : Char -> WordAnalysis -> WordAnalysis
updateAnalysis char dict =
  Dict.update (Char.toLower char) updateCount dict

analyzeWord : String -> WordAnalysis
analyzeWord word =
  String.foldr updateAnalysis Dict.empty word

isAnagram : String -> String -> Bool
isAnagram word1 word2 =
  analyzeWord word1 == analyzeWord word2


-- test functions

anagramTests : List (String, String)
anagramTests =
  [ ("stressed", "desserts")
  , ("stressed", "deserts")
  , ("marching", "charming")
  , ("happy", "sad")
  ]

renderTest : (String, String) -> Html msg
renderTest (word1, word2) =
  div []
    [ u [] [ text word1 ]
    , text " and "
    , u [] [ text word2 ]
    , if isAnagram word1 word2 then
        span
          [ style [ ( "color", "green" ), ("font-weight", "bold") ] ]
          [ text " are anagrams" ]
      else
        span [] [ text " are not anagrams" ]
    ]

main =
  div [] ( List.map renderTest anagramTests )