Haskell file reading and adding of numbers

Question

I have a program that takes a text file with values for example:

20 30
23 5
200 3

And I convert it to a list and add each line to create a subtotal and then a sum.

import System.IO  
import Control.Monad

f :: [String] -> [Int]
f = map read

subsum :: [Int] -> [Int]
subsum [] = []
subsum [x] = []
subsum (x:(y:xs)) = (x+y) : (subsum xs)

calc fromf = do  
        let list = []  
        let list2 = []
        handle <- openFile fromf ReadMode
        contents <- hGetContents handle
        let singlewords = words contents
            list = f singlewords
            list2 = subsum list
            result = sum list2
        print list2
        print result
        hClose handle

How would I change this code to take in a text file of different numbers ex:

10 9 29 40
1 34 2
1 2 55 89

Create a list of subtotals of each line and then a total.

Your list = [] and list2 = [] statements are unnecessary. These are not mutable variables (as is the case with other languages), so you're not accomplishing anything like initialization, as you may imagine. — Adam Wagner
– Adam Wagner, Commented Oct 24, 2011 at 1:43

fs. · Accepted Answer · 2011-10-24 01:19:45Z

2

How about

import System.IO
import Control.Monad

subtotals :: String -> [Int]
subtotals c = map sum (map (map readInt) (map words (lines c)))
    where
        readInt = read :: String -> Int

calc fname = do
    contents <- readFile fname
    print $ subtotals contents
    print $ sum (subtotals contents)

answered Oct 24, 2011 at 1:19

fs.

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1 Comment

alxp Over a year ago

readInt is undefined on my stock GHC 7.10.2. I replaced it with my own function " readInt :: [String] -> [Int]; readInt = map read"

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