5 ms·

Perhaps TCO is not required for idiomatic Clojure, but for advanced functional programming using e.g. Monads or CPS, TCO is absolutely necessary in practice.

• dragandj 10y ago
  Clojure has TCO, though. This is what recur is for.
  • willtim 10y ago
    No Clojure does not have TCO, due to the JVM. It allows you to manually optimise self-recursion via recur. This is not enough for many advanced FP techniques, such as CPS. For example, using CPS and TCO, I can traverse a tree in constant stack space. I agree with the parent that lack of TCO in Clojure is probably not an issue for most.
    • jjnoakes 10y ago
      If you are traversing a tree in constant stack space, the closures your continuations are holding on to must be O(ln) in space and representing what would have been on the stack, right?
      • willtim 10y ago
        Yes absolutely, I'd be trading stack for heap.
• brandonbloom 10y ago
  The fact that monads are not popular in Clojure is a good thing, IMHO. Besides, test.check and clojure.spec get by just fine with macros for generator monads. It's not quite perfect, and everyone would like proper tail calls, but it's far from an impediment for the overwhelming majority of tasks tackled with Clojure.
  • willtim 10y ago
    I have already stated that it is quite possibly not a problem for Clojure, although this hasn't stopped all the downvotes I keep getting (which doesn't leave me with a good impression of Clojure users). My point is that, despite the claims of the parent post, TCO is needed for many advanced functional programming techniques.
    • brandonbloom 10y ago
      You're being down voted because you keep repeating a claim without evidence despite both evidence to the contrary and acknowledgement of the utility of tail calls.
      • willtim 10y ago
        No, I have been disputing the following parent claim: > The idea that TCO is needed to "fully" leverage anything is silly. I provided two examples, monads and CPS transforms, which require TCO to fully leverage in a strict language. But really any example where functions are dyamically composed as a pipeline needs TCO to avoid leaking stack. Your examples of a couple of test libraries in Clojure hardly constitute evidence that TCO is of limited utility.
        • brandonbloom 10y ago
          > any example where functions are dyamically composed as a pipeline needs TCO to avoid leaking stack Sure, but in the rare case that this is a problem, you can trivially workaround it: (reduce (fn [acc f] (f acc)) init [f1 f2 f3]) This approach may not match the Haskell ideal of FP, but it's actually got many significant advantages. Frequently, programming with data structures is _better_ than programming with function composition. For example, you may choose to do something like this: (reduce (fn [acc f] (println "executing" f) (f acc)) init [#'f1 #'f2 #'f3]) Where this is now a pipeline with logging of the stages. You can't do that if you prematurely select function composition as your primary way to structure computations. The Haskell research community is in the process of undoing this brain damage on the monad front by embracing extensible effects, free(-er) monads, "reflection without remorse", effect interpreters, etc. Once you need any sort of symbolic reasoning, you drop opaque composition and work with data. This is true in every language, FP or not. People tend to do exactly the right thing already: abandon function combinators and write interpreters over data structures.