Sums numbers on the command line.

total.hs

#! /usr/bin/env stack
-- stack --resolver lts-8.15 --install-ghc script --package base
{-# LANGUAGE ScopedTypeVariables #-}

-- Usage:
--   $ echo -e "1.2 3.4\n5.6 not-a-number" | ./total.hs
--   10.2

import Data.Maybe (mapMaybe)
import Text.Read (readMaybe)

main = print . sum . mapMaybe (readMaybe :: String -> Maybe Double) . words =<< getContents