This has always felt like the kind of thing we could be building compilers to solve. Recursive -> explicit stack is a very mechanical conversion, why can't we write a compiler transform pass that does that rewrite any time it detects a high potential for stack overflow?
Jaxan•Mar 14, 2026
Many compilers do change a recursion into a loop, avoiding the stack altogether!
Epa095•Mar 14, 2026
Yeah, tail call elimination, is definitely doable.
Python famously does not have it because "Language inventor Guido van Rossum contended that stack traces are altered by tail-call elimination making debugging harder, and preferred that programmers use explicit iteration instead".
https://en.wikipedia.org/wiki/Tail_call
derriz•Mar 14, 2026
It’s called TCO - tail call optimization - and gcc and llvm are supposed to implement it although tail recursive style code is probably uncommon in C or C++. Outside of that it’s common in functional languages where recursive functions are obviously idiomatic and so it has more potential to provide performance benefit.
It’s not a purely local optimization - affecting the call structure so debugging is a pain point. Which is probably why most imperative language compilers don’t bother given the lack of utility for the vast majority of code bases.
It feels like something that would need to be specified at the language spec or semantics level to make it useful rather than just making it optional for the compiler - otherwise the developer is probably just going to do the transform manually - to be safe - if stack explosion was a possibility if the compiler decided on a whim to not perform TCO.
afiori•Mar 14, 2026
Just like many languages have annotations for inlining functions they could have annotations for tco. From an usability pov i would like annotations for must, must not, should, and should not. Where the "must" versions error if the compiler can't do the optimization
a57721•Mar 14, 2026
Scala and Kotlin have 'tailrec' annotation/modifier, though not as sophisticated as you describe.
ufo•Mar 14, 2026
Tail call optimization optimizes the situations where the recursion doesn't actually need any stack space, but I think the parent poster is asking about situations that aren't tail recirsive.
ufo•Mar 14, 2026
It's indeed very mechanical and some programming languages can do it for you.
I think you're mainly asking for heap-allocated stacks. Some languages always use the heap for stack frames instead of the native stack and can set the stack limit as high as there's memory available.
You might also want to look into stackful coroutines, which allow one to pause the execution of a recursive function and switch to another function. This can provide you with multiple call stacks, which is another reason people sometimes choose to use write explicit stacks.
jonathanlydall•Mar 14, 2026
It depends on whether the limited call stack capacity will be an issue for the particular problem you’re solving.
I’m presently working on a problem which uses traversal of TypeScript file syntax trees.
I can reasonably assume that we will never get a file with a deep enough syntax tree which would cause a stack overflow.
A manually managed stack might seem safer, but as pointed out by this article the code would be more complicated and, in my case, for no good reason.
layer8•Mar 14, 2026
In practice, a heap-based manual stack can be as unsafe with unbounded input as using the native call stack (considering typical OOM behavior). If you have untrusted input, you might want to limit the stack depth in either case. And it’s not difficult to add a recursion counter to recursive calls. So I don’t think it’s an inherently distinguishing feature between the two approaches.
Personally I tend to find the iterative approach easier to follow when no actual stack is needed, i.e. in the tail-call case.
randomNumber7•Mar 14, 2026
> I can reasonably assume that we will never get a file with a deep enough syntax tree which would cause a stack overflow.
What if eve constructs a file specifically so that you get stack overflow?
jonathanlydall•Mar 14, 2026
Eve will then experience a stack overflow exception on our app running on her PC, no doubt she will be very impressed with her achievement.
aleph_minus_one•Mar 14, 2026
>
It depends on whether the limited call stack capacity will be an issue for the particular problem you’re solving.
First: that common programming languages use the limited call stack for implementing recursion is an artifact of the programming language (implementation). One can, for example, use a stack data structure for implementing DFS instead of using the call stack; it would be no problem for a programming language implementation to use a similar method for implementing recursion.
This said: there actually exist two kinds of recursion (barely every computer science textbooks at most barely mentions this):
1. "normal" recursion (with all its problems such as potential stack overflow etc.)
2. tail recursion with guaranteed tail-call elimination (TCE) in the programming language semantics; then recursion basically behaves "like loops".
I want to clarify that it is a common exercise to convert a program that uses "normal" recursion to one that uses tail-recursion, just like it is a common exercise to convert such a program to one that uses imperative style.
jonathanlydall•Mar 14, 2026
Yes, languages and/or engines with this feature can eliminate any concerns about stack overflows.
But in this particular case I'm using JavaScript (since at this time it has the best libraries for working with TypeScript ASTs) running under Node.js, and my understanding is that is has no tail call optimization.
The other language I mostly work in is C#, which also similarly lacks it.
So, at this time in the languages I work in, I need to consider possible stack overflows whenever I use recursion.
twic•Mar 14, 2026
> It seems to be common knowledge that any recursive function can be transformed into an iterative function.
Huh. Where i work, the main problem is that everyone is hell-bent on transforming every iterative function into a recursive function. If i had a pound for every recursive function called "loop" in the codebase, i could retire.
skeeter2020•Mar 14, 2026
My experience has gone the other way: lots of code with recursion, rewritten to be iterative. There really aren't that many use-cases in vanilla enterprise code that benefit from recursion when the entire cost is considered.
adafactor•Mar 14, 2026
Where on earth do you work? This is unusual...
twic•Mar 14, 2026
> This solution looks extremely similar to the previous one, which is a good thing. Our requirements have experienced a small change (reversing the traversal order) and our solution has responded with a small modification.
Now do breadth-first traversal. With the iterative approach, you just replace the stack with a queue. With the recursive approach, you have to make radical changes. You can make either approach look natural and elegant if you pick the right example.
aleph_minus_one•Mar 14, 2026
> Now do breadth-first traversal. With the iterative approach, you just replace the stack with a queue. With the recursive approach, you have to make radical changes.
The reason is that no programming language that is in widespread use has first-class support for co-recursion. In a (fictional) programming language that has this support, this is just a change from a recursive call to a co-recursive call.
Chinjut•Mar 14, 2026
Haskell (I realize this may not pass your threshold for widespread use) has equal support for co-recursion as for structural recursion.
naasking•Mar 14, 2026
True, but couldn't you just simulate it by enqueing a thunk/continuation?
twic•Mar 14, 2026
Right, you could use co-recursion. Or you could just use a queue.
lacoolj•Mar 14, 2026
This page is a good example of when Typescript is both unnecessary and off-putting, based on the content's purpose.
The author is trying to demonstrate a problem and the proposed solution, using example code that the reader then needs to read, formulate a visual "structure" in their mind, and then apply that structure to the subsequent code.
Typescript is not in any way invalid here, and as a tool when programming something that will run in the real-world, can be invaluable.
However, when writing anything you want someone to deeply comprehend, you want to use the least amount of text needed to get your point across. Adding types don't serve any purpose here. The types used are generics, which tell you nothing specific, hence the name, and the names given to the functions and object properties are enough to convey what this code is doing.
adafactor•Mar 14, 2026
PL-specific problem, but: the Rust borrow checker tends to give you a lot of trouble when writing iterative algorithms on nonlinear data structures, because it has trouble reasoning about partial borrows.
The upcoming Polonius borrow checker is supposed to solve this, but it's still in alpha...
fifilura•Mar 14, 2026
Recursive solutions benefit from recursive solutions unless the solution is trivial.
7 Comments
Python famously does not have it because "Language inventor Guido van Rossum contended that stack traces are altered by tail-call elimination making debugging harder, and preferred that programmers use explicit iteration instead". https://en.wikipedia.org/wiki/Tail_call
It’s not a purely local optimization - affecting the call structure so debugging is a pain point. Which is probably why most imperative language compilers don’t bother given the lack of utility for the vast majority of code bases.
It feels like something that would need to be specified at the language spec or semantics level to make it useful rather than just making it optional for the compiler - otherwise the developer is probably just going to do the transform manually - to be safe - if stack explosion was a possibility if the compiler decided on a whim to not perform TCO.
I think you're mainly asking for heap-allocated stacks. Some languages always use the heap for stack frames instead of the native stack and can set the stack limit as high as there's memory available.
You might also want to look into stackful coroutines, which allow one to pause the execution of a recursive function and switch to another function. This can provide you with multiple call stacks, which is another reason people sometimes choose to use write explicit stacks.
I’m presently working on a problem which uses traversal of TypeScript file syntax trees.
I can reasonably assume that we will never get a file with a deep enough syntax tree which would cause a stack overflow.
A manually managed stack might seem safer, but as pointed out by this article the code would be more complicated and, in my case, for no good reason.
Personally I tend to find the iterative approach easier to follow when no actual stack is needed, i.e. in the tail-call case.
What if eve constructs a file specifically so that you get stack overflow?
First: that common programming languages use the limited call stack for implementing recursion is an artifact of the programming language (implementation). One can, for example, use a stack data structure for implementing DFS instead of using the call stack; it would be no problem for a programming language implementation to use a similar method for implementing recursion.
This said: there actually exist two kinds of recursion (barely every computer science textbooks at most barely mentions this):
1. "normal" recursion (with all its problems such as potential stack overflow etc.)
2. tail recursion with guaranteed tail-call elimination (TCE) in the programming language semantics; then recursion basically behaves "like loops".
I want to clarify that it is a common exercise to convert a program that uses "normal" recursion to one that uses tail-recursion, just like it is a common exercise to convert such a program to one that uses imperative style.
But in this particular case I'm using JavaScript (since at this time it has the best libraries for working with TypeScript ASTs) running under Node.js, and my understanding is that is has no tail call optimization.
The other language I mostly work in is C#, which also similarly lacks it.
So, at this time in the languages I work in, I need to consider possible stack overflows whenever I use recursion.
Huh. Where i work, the main problem is that everyone is hell-bent on transforming every iterative function into a recursive function. If i had a pound for every recursive function called "loop" in the codebase, i could retire.
Now do breadth-first traversal. With the iterative approach, you just replace the stack with a queue. With the recursive approach, you have to make radical changes. You can make either approach look natural and elegant if you pick the right example.
The reason is that no programming language that is in widespread use has first-class support for co-recursion. In a (fictional) programming language that has this support, this is just a change from a recursive call to a co-recursive call.
The author is trying to demonstrate a problem and the proposed solution, using example code that the reader then needs to read, formulate a visual "structure" in their mind, and then apply that structure to the subsequent code.
Typescript is not in any way invalid here, and as a tool when programming something that will run in the real-world, can be invaluable.
However, when writing anything you want someone to deeply comprehend, you want to use the least amount of text needed to get your point across. Adding types don't serve any purpose here. The types used are generics, which tell you nothing specific, hence the name, and the names given to the functions and object properties are enough to convey what this code is doing.
The upcoming Polonius borrow checker is supposed to solve this, but it's still in alpha...