While in Haskell

In Haskell, the while construct is not available in the standard library, but it can be easily defined using recursion.

Here is an example of how to define while function using recursion:

-- Define a while function that takes a condition and an action
while :: (a -> Bool) -> (a -> a) -> a -> a
while condition action a
  -- Base case: if the condition is no longer true, return a
  | not (condition a) = a
  -- Recursive case: apply the action to a and continue the loop
  | otherwise = while condition action (action a)

Here is an example of how to use the while function:

-- Define a condition and an action
condition :: Int -> Bool
condition i = i < 10
action :: Int -> Int

action i = i + 1
-- Use the while function to repeatedly apply the action until the condition is no longer true

result = while condition action 0
-- Output: 10

In this example, the while function is used to repeatedly apply the action function to the variable a until the condition is no longer true. The result variable will hold the value of a when the loop terminates.