>>45
そこんところに適用されていく様子が書いてあるでしょ。
wordNums "wa wa wee wa"なら

words "wa wa wee wa" 　→　["wa", "wa", "wee", "wa"]
sort ["wa", "wa", "wee", "wa"] → ["wa", "wa", "wa", "wee"]
group ["wa", "wa", "wa", "wee"] → [ ["wa","wa","wa"], ["wee"] ]
map (¥ws->(head ws, length ws)) [ ["wa","wa","wa"], ["wee"] ] → [("wa",3),("wee",1)]

で、一目瞭然だと思うんだけどなにが分かんないの？
ポイントフリーだから混乱してるとかそういう話？

wordNums xs = map (¥ ws -> (head ws, length ws)) $ group $ sort $ words xs

敢えて最後に引数補ってこう書いてあればわかったりするのかしら。