Haskell：将字符串转换为 [(String,Double)]

Question

I parse an XML and get an String like this:

"resourceA,3-resourceB,1-,...,resourceN,x"

I want to map that String into a list of tuples (String,Double), like this:

[(resourceA,3),(resourceB,1),...,(resourceN,x)]

How is it possible to do this? I ve looked into the map function and also the split one. I am able to split the string by "-" but anything else...

This is the code i have so far:

split :: Eq a => a -> [a] -> [[a]]
split d [] = []
split d s = x : split d (drop 1 y) where (x,y) = span (/= d) s

it is just a function to split my string into a list of Stirng, but then i dont know how to continue. What I want to do know is to loop over that new list that i have created with the split method and for each element create a tuple. I hace tried with the map function but i dont get it to compile even

Answer 1

So in Haskell you dont really mutate any value, instead you'll create a new list of pairs from the string you've described, so the solution would look something similar to the following:

import Data.List.Split


xmlList = splitOn "-" "resourceA,3-resourceB,4-resourceC,6"

commaSplit :: String -> [String]
commaSplit = splitOn ","

xmlPair :: [String] -> [(String, Double)] -- might be more efficient to use Text instead of String
xmlPair [x]    = [(\x' -> ((head x') :: String, (read (last x')) :: Double )) (commaSplit x)]
xmlPair (x:xs) = xmlPair [x] ++ xmlPair xs

main :: IO ()
main = mapM_ (\(a,b) -> putStrLn (show a++" = "++ show b)) (xmlPair $ xmlList)

This is my quick and dirty way of showing things but I'm sure someone can always add a more detailed answer.