Because patterns are matched in order and the first one match is taken.
The standard Prelude implementation of 'last' is as follows
\begin{code}
last :: [a] -> a
last [x] = x
last (_:xs) = last xs
last [] = error "Prelude.last: empty list"
\end{code}
Isn't [x] equivalent to (x:[]) hence wouldn't [1] match both [x] and
(_:xs)? If that's the case then we would have
last [1] == 1
and
last [1] == last []
but that doesn't happen. Why?
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