Capitalize Every Other Letter in a String -- take / drop versus head / tail for Lists -

i have spent past afternoon or 2 poking @ computer if had never seen 1 before. today's topic lists

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the exercise take string , capitalize every other letter. did not far...

let's take list x = string.tolist "abcde" , try analyze it. if add results of take 1 , drop 1 original list

> x = string.tolist "abcde" ['a','b','c','d','e'] : list char > (list.take 1 x) ++ (list.drop 1 x) ['a','b','c','d','e'] : list char 

i thought head , tail did same thing, big error message:

> [list.head x] ++ (list.tail x) ==================================== errors ====================================  -- type mismatch --------------------------------------------- repl-temp-000.elm  right argument of (++) causing type mismatch.  7│   [list.head x] ++ (list.tail x)                        ^^^^^^^^^^^ (++) expecting right argument a:      list (maybe char)  right argument is:      maybe (list char)  hint: figure out type of left argument first , if acceptable on own, assume "correct" in subsequent checks. problem may in how left , right arguments interact. 

the error message tells me lot of what's wrong. not 100% sure how fix it. list joining operator ++ expecting [maybe char] , instead got maybe [char]

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let's try capitalize first letter in string (which less cool, realistic).

[string.toupper ( list.head  x)] ++  (list.drop 1 x) 

this wrong since char.toupper requires string , instead list.head x maybe char.

[char.toupper ( list.head  x)] ++  (list.drop 1 x) 

this wrong since char.toupper requires char instead of maybe char.

in real life user break script typing non-unicode character (like emoji). maybe elm's feedback right. should easy problem takes "abcde" , turns "abcde" (or possibly "abcde"). how handle errors properly?

• the same question in javascript: how make first letter of string uppercase in javascript?

in elm, list.head , list.tail both return maybe type because either function passed invalid value; specifically, empty list. languages, haskell, throw error when passing empty list head or tail, elm tries eliminate many runtime errors possible.

because of this, must explicitly handle exceptional case of empty list if choose use head or tail.

note: there better ways achieve end goal of string mixed capitalization, i'll focus on head , tail issue because it's learning tool.

since you're using concatenation operator, ++, you'll need list both arguments, it's safe create couple functions handle maybe return values , translate them empty list, allow use concatenation operator.

myhead list =   case list.head list of     h -> [h]     nothing -> []  mytail list =   case list.tail list of     t -> t     nothing -> [] 

using case statements above, can handle possible outcomes , map them usable circumstances. can swap myhead , mytail code , should set.