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    <p>Honestly, any problem that you can solve with a loop is already a naturally recursive one, as you can translate both into (usually conditional) jumps in the end.</p> <p>I believe you should stick with tail calls in almost all cases where you must write an explicit loop. It is just more versatile:</p> <ul> <li>A while loop restricts you to one loop body, while a tail call can allow you to switch between many different states while the "loop" is running.</li> <li>A while loop restricts you to one condition to check for termination, with the tail recursion you can have an arbitrarily complicated match expression waiting to shunt the control flow off somewhere else.</li> <li>Your tail calls all return useful values and can produce useful type errors. A while loop does not return anything and relies on side effects to do its work.</li> <li>While loops are not first class while functions with tail calls (or while loops in them) are. Recursive bindings in local scope can be inspected for their type.</li> <li>A tail recursive function can easily be broken apart into parts that use tail calls to call each other in the needed sequence. This may make things easier to read, and will help if you find you want to start in the middle of a loop. This is not true of a while loop.</li> </ul> <p>All in all while loops in F# are only worthwhile if you really are going to be working with mutable state, inside a function body, doing the same thing repeatedly until a certain condition is met. If the loop is generally useful or very complicated, you may want to factor it out into some other top level binding. If the data types are themselves immutable (a lot of .NET value types are), you may gain very little from using mutable references to them anyway. </p> <p>I'd say that you should only resort to while loops for niche cases where a while loop is perfect for the job, and is relatively short. In many imperative programming languages, while loops are often twisted into unnatural roles like driving stuff repeatedly over a case statement. Avoid those kinds of things, and see if you can use tail calls or, even better, a higher order function, to achieve the same ends.</p>
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