Why is this Haskell program so much slower than an equivalent Python one?

Question

As part of a programming challenge, I need to read, from stdin, a sequence of space-separated integers (on a single line), and print the sum of those integers to stdout

Answer 1

Read is slow

Fast read, from this answer, will bring you down to 5.5 seconds.

import Numeric
fastRead :: String -> Int
fastRead s = case readDec s of [(n, "")] -> n

Strings are Linked Lists

In Haskell the String type is a linked list. Using a packed representation (bytestring if you really only want ascii but Text is also very fast and supports unicode). As shown in this answer, the performance should then be neck and neck.