CODEWITHSUNDEEP
haskell
Alex
Alex

Reputation: 325

How to break up a sentence (String) into a list ([String])?

I have the following code:

    realWord :: String -> String
    realWord s = if elem (map toLower s) ["the","a","of","in","at"] then "" else (map toLower s)

This is to test if a string like "the godfather" contains any number of trivial words such as "the". However, when I put "the godfather" into the function, clearly it gives that this string isn't contained in the list, and spits the sentence out again.

How do I break the sentence "the godfather" into a list of words that I can test individually and then put back together again in a sentence?

My desired output for input "the godfather" is "godfather".

Upvotes: 1

Views: 849

Answers (2)

leftaroundabout
leftaroundabout

Reputation: 120711

First of all, DRY:

realWord s 
    | s' `elem` trivial  = ""
    | otherwise          = s'
  where trivial = ["the","a","of","in","at"]
        s' = map toLower s

So. The problem is, you're not deconstructing the string in any way. What you're trying to do is matching on something and "consuming & throwing away" it when found – that's actually a very basic subtask of parsing.

For this problem, Niklas' solution is probably the best, but to make this more general it's simple enough to use one of the "big weapons":

import Text.Parsec

extractRealWord :: Parsec String u String
extractRealWord = do
      skipMany . choice
         . map (\w -> string w >> many (oneOf ",. !?\n"))
            $ ["the", "a", "of", "in", "at"]
                            >>= \w@(f:r) -> [w, toUpper f : r]
      many . oneOf $ ['a' .. 'z'] ++ ['A' .. 'Z']

To be used e.g.

Prelude Text.Parsec Data.Char> runP extractRealWord ()[] "the godfather"
Right "godfather"

Upvotes: 0

Niklas B.
Niklas B.

Reputation: 95308

You can use the Prelude functions words and unwords:

realWord = unwords . filter (`notElem` trivial) . words . toLower
    where trivial = ["the","a","of","in","at"]

Upvotes: 9

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