Answer:
A functionalist or the theory of functionalism believes that the society works in a rigid structure where everyone supports the other.
The world is interlinked and all of us serve a biological and social purpose which has an impact on us and the community we live in.
In this view, Walmart, squeezing vendors for low prices in order to provide rock-bottom prices to the end customer is just an example of how a social structure is working.
This, in the view of a functionalist, is how the world works and Walmart is able to fulfill an actual need in the market by forcing vendors to make less margins.
It might have it's own impact on small businesses, but at the end, Walmart is profitable which shows, it is actually meeting the needs of a society.