What’s the right way to divide two Int values to obtain a Float?

You have to convert the operands to floats first and then divide, otherwise you’ll perform an integer division (no decimal places).

Laconic solution (requires Data.Function)

foo = (/) `on` fromIntegral

which is short for

foo a b = (fromIntegral a) / (fromIntegral b)

with

foo :: Int -> Int -> Float