Question

Type class Integral has two operations quot and div, yet in the Haskell 2010 Language Report it is not specified what they’re supposed to do. Assuming that div is integral division, what does quot differently, or what is the purpose of quot? When do you use one, and when the other?

Answer 1

To quote section 6.4.2 from the Haskell report:

The quot, rem, div, and mod class methods satisfy these laws if y is non-zero:

(x `quot` y)*y + (x `rem` y) == x  
(x `div`  y)*y + (x `mod` y) == x

quot is integer division truncated toward zero, while the result of div is truncated toward negative infinity.

The div function is often the more natural one to use, whereas the quot function corresponds to the machine instruction on modern machines, so it’s somewhat more efficient.