while is:exact

A binary pattern is used to conditionally apply a function to a source pattern. The function is applied when a True value is active, and the pattern is let through unchanged when a False value is active. No events are let through where no binary values are active.

A while loop, run the second argument while the first argument is true. The action is run in a scope. See also loop.

x <- mutable_ x
while (x %< 10) $ do
x @= x + 1