smsing like in the old days

algebraic-types-phone.hs

import Data.Char
import Data.List
import Data.Map (Map)
import qualified Data.Map.Strict as Map

{-|
 ---------------------------
 | 1      | 2 ABC | 3 DEF  |
 ___________________________
 | 4 GHI  | 5 JKL | 6 MNO  |
 ---------------------------
 | 7 PQRS | 8 TUV | 9 WXYZ |
 ---------------------------
 | * ^    | 0 + _ | # .,   |
 ---------------------------
-}

type Digit = Char
type Presses = Int
type Key = Char
type Chars = String

data DaPhone = DaPhone (Map.Map Key Chars) deriving (Show)
data InverseDaPhone = InverseDaPhone (Map.Map Char Key) deriving (Show)

unpackInverseDaPhone :: InverseDaPhone -> (Map.Map Char Key)
unpackInverseDaPhone (InverseDaPhone mapping) = mapping

phoneToList :: DaPhone -> [(Key, Chars)]
phoneToList (DaPhone kvs) = Map.toList kvs

phoneFromList :: [(Char, String)] -> DaPhone
phoneFromList lst = DaPhone (Map.fromList lst)

inversePhoneFromList :: [(Char, Char)] -> InverseDaPhone
inversePhoneFromList lst = InverseDaPhone (Map.fromList lst)

inversePhone :: DaPhone -> InverseDaPhone
inversePhone phone = inversePhoneFromList $ foldr (++) [] (map (
    \(kkey, chars) -> map (
        \char -> (char, kkey)) chars) (phoneToList phone))

charsAtKey :: Key -> DaPhone -> Chars
charsAtKey key (DaPhone kvs) =
    let
        lu = Map.lookup key kvs
    in case lu of
        Just val -> val
        Nothing -> error "well someone didn't validate the data. naughty naughty."

charAtKey :: Char -> DaPhone -> Key
charAtKey char phone =
    let
        charToKey = inversePhone phone
        lu = Map.lookup char $ unpackInverseDaPhone charToKey
    in case lu of
        Just key -> key
        Nothing -> error "well someone didn't validate the data. naughty naughty."

reverseTaps :: DaPhone -> Char -> [(Digit, Presses)]
reverseTaps phone char =
    let key = charAtKey char phone
        maybeElemIndex = elemIndex char (charsAtKey key phone )
        presses = case maybeElemIndex of
                        Just elemIndex -> elemIndex
                        Nothing -> error "well that didn't work out as intended mister. invalid char."
    in
       if isLower char then [('*', 1)] ++ reverseTaps phone (toUpper char)
       else [(key, presses)]

cellPhonesDead :: DaPhone -> String -> [(Digit, Presses)]
cellPhonesDead phone text = foldr (++) [] $ map (\x -> reverseTaps phone x) text


keyboardDefinition = [
    ('1', "1"),
    ('2', "ABC2"),
    ('3', "DEF3"),
    ('4', "GHI4"),
    ('5', "JKL5"),
    ('6', "MNO6"),
    ('7', "PQRS7"),
    ('8', "TUV8"),
    ('9', "WXYZ9"),
    ('*', "*^"),
    ('0', " +_0"),
    ('#', "#.,")]

phoneDef = phoneFromList keyboardDefinition

-- example
-- 'a' -> [('2', 1)]
-- 'A' -> [('*', 1), ('2', 1)]


-- test
-- *Main Data.List Data.Maybe> reverseTaps phoneDef 'A'
-- [('2',0)]
-- *Main Data.List Data.Maybe> reverseTaps phoneDef 'a'
-- [('*',1),('2',0)]
-- *Main Data.List Data.Maybe> cellPhonesDead phoneDef "AA"
-- [('2',0),('2',0)]
-- *Main Data.List Data.Maybe> cellPhonesDead phoneDef "aa bb"
-- [('*',1),('2',0),('*',1),('2',0),('0',0),('*',1),('2',1),('*',1),('2',1)]