Define a haskell function named “addUs” that adds 2 input numbers.
Using this function as a building block, define a Haskell function “multiplyUs” that
multiplies two input numbers.
The multiplyUs function should cater to following:
1. Inputs may be signed numbers e.g. “multiplyUs (-2) * (3)” should result in “-6”
and “multiplyUs (-2) * (-6)” should result in “12”
2. It should use guard expressions and recursion.
3. No need to write the main function to do user interaction writing definition for
“addUs” and “multiplyUs” is sufficient