Explain how filter and find functions work on lists in functional programming.

In functional programming, filter and find functions are used to manipulate lists based on certain conditions.

The filter function is a higher-order function that processes a data list based on a given condition. It takes two arguments: a function and a list. The function is applied to each element of the list. If the function returns true for an element, that element is included in the new list. If the function returns false, the element is excluded. The filter function returns a new list and does not modify the original list. This is in line with the principles of functional programming, where data is immutable and functions have no side effects.

For example, consider a list of numbers and a function that checks if a number is even. If you apply the filter function with this condition to the list, you will get a new list that only contains the even numbers from the original list.

The find function, on the other hand, is used to find the first element in a list that satisfies a certain condition. Like the filter function, it also takes a function and a list as arguments. The function is applied to each element of the list in order, and as soon as an element is found for which the function returns true, that element is returned by the find function. If no such element is found, the find function returns a special value, often null or undefined.

For instance, if you have a list of numbers and a function that checks if a number is greater than 10, the find function will return the first number in the list that is greater than 10. If there are no numbers greater than 10 in the list, the function will return null or undefined.

In summary, filter and find are powerful functions in functional programming that allow you to manipulate lists based on certain conditions. They embody the principles of functional programming by being stateless and producing no side effects.