On Tue, Feb 10, 2015 at 7:58 PM, Joel Neely <joel.neely@gmail.com> wrote:

sumDigits (n:ns)
| n < 10 = n + sumDigits ns
| n >= 10 = r + sumDigits (q : ns)
where (q, r) = n `quotRem` 10

To reiterate what Mike and Brandon just said, it's not that both the [] and (n:ns) cases have not been covered. They have.

It's that the (n:ns) case hasn't been covered completely because of the guards.

This will work:

sumDigits (n:ns)

| n < 10 = n + sumDigits ns

| otherwise = r + sumDigits (q : ns)

As will this:

sumDigits (n:ns)

| n < 10 = n + sumDigits ns

| n >= 10 = r + sumDigits (q : ns)

| otherwise = error "will never fire, only to suppress spurious warning"

There's also -fno-warn-incomplete-patterns.

-- Kim-Ee