functional programming - While or Tail Recursion in F#, what to use when?

Question

Ok, only just in F# and this is how I understand it now :

• Some problems are recursive in nature (building or reading out a treestructure to name just one) and then you use recursion. In these cases you preferably use tail-recursion to give the stack a break

• Some languagues are pure functional, so you have to use recursion in stead of while-loops, even if the problem is not recursive in nature

So my question : since F# also support the imperative paradigm, would you use tail recursion in F# for problems that aren't naturally recursive ones? Especially since I have read the compiler recongnizes tail recursion and just transforms it in a while loop anyway?

If so : why ?

Answer 1

The best answer is 'neither'. :)

There's some ugliness associated with both while loops and tail recursion.

While loops require mutability and effects, and though I have nothing against using these in moderation, especially when encapsulated in the context of a local function, you do sometimes feel like you're cluttering/uglifying your program when you start introducing effects merely to loop.

Tail recursion often has the disadvantage of requiring an extra accumulator parameter or continuation-passing style. This clutters the program with extra boilerplate to massage the startup conditions of the function.

The best answer is to use neither while loops nor recursion. Higher-order functions and lambdas are your saviors here, especially maps and folds. Why fool around with messy control structures for looping when you can encapsulate those in reusable libraries and then just state the essence of your computation simply and declaratively?

If you get in the habit of often calling map/fold rather than using loops/recursion, as well as providing a fold function along with any new tree-structured data type you introduce, you'll go far. :)

For those interested in learning more about folds in F#, why not check out my first three blog posts in a series on the topic?