Question

Hi i’m getting a (Line 7) Parse error in input “=” for this which just sums the words in a string, any help is appreciated. Thanks.

module Main where

main = do
 putStr "Enter a string: "
 input <- getContents

 value = unwords . sum . words input
 putStrLn (value)

Answer 1

The line:

value = unwords . sum . words input

Is not syntactically valid. You need a let statement.

let value = unwords . sum . words input

This still isn’t valid, you want to apply your function (well, composition of three functions) to the input:

let value = (unwords . sum . words) input

or perhaps:

let value = unwords . sum . words $ input

This still isn’t valid because the input is a String and the result of words is a list of String ([String]). So you’ll want to read the strings into some Num type (Integers?) then convert back to String. unwords is not useful because you only have one word, the sum, left at the end (vs a list of words, which unwords would need):

let value = show . sum . map read. words $ input

Depending on the type, you might want to annotate the read or the sum to specify if it’s an Int or a Double or something else.