# TCO - Tail Call Optimization TCO is a technique used by some compilers and interpreters to optimize recursive [[Function]] [[Call|calls]] that occur in the "tail position." The tail position is when a [[Function]] [[call]] is the last action performed by a [[Function]] before it returns a result. It reduce the [[Memory]] overhead associated with [[Function]] [[Call|calls]], allowing for more efficient execution of programs that rely heavily on [[recursion]]. ## Key Concepts: 1. **Tail Call**: - A [[Tail call]] is a [[Function]] [[call]] that is the last operation in another [[Function]]. After this [[call]] returns, there’s nothing left to do in the current [[Function]]. - Example: ```python def tail_call_example(x): return another_function(x) # Tail call ``` 1. **Tail Recursion**: - Tail [[recursion]] is a specific kind of [[recursion]] where the recursive [[call]] is the last operation in the [[Function]]. - Example: ```python def factorial(n, acc=1): if n == 0: return acc return factorial(n-1, n*acc) # Tail recursive call ``` 1. **Optimization**: - In languages or compilers that support TCO, the stack frame of the current [[Function]] can be reused for the [[Tail call]] instead of creating a new stack frame. This prevents the potential stack overflow that could occur with deep [[recursion]] and allows the [[recursion]] to run in constant space. - Without TCO, every [[Function]] [[call]] would add a new stack frame, eventually leading to stack overflow in deeply recursive [[Function|functions]]. ## Benefits of TCO: - **Space Efficiency**: By reusing the stack frame, TCO reduces the amount of [[Memory]] used (from O(n) to O(1)), preventing stack overflow. - **Performance**: It can make certain recursive algorithms run faster because it avoids the overhead of additional stack frames. ## Examples in Different Languages: - **Python**: - [[Python]] does not perform TCO by default due to its design philosophy, which emphasizes debugging and traceability over optimization. However, tail [[recursion]] can be manually optimized by converting the [[recursion]] into a loop. ```python def factorial(n, acc=1): if n == 0: return acc return (n-1, n*acc) args = (5,) while isinstance(args, tuple): args = factorial(*args) else: # When we exit the loop res = args # args are not the result ``` - **Scheme**: - Scheme, a dialect of Lisp, is well-known for its support of TCO, and many functional languages like Haskell and Scala also support it. ```scheme (define (factorial n) (fact-iter 1 n)) (define (fact-iter product n) (if (= n 0) product (fact-iter (* product n) (- n 1)))) ; Tail call ``` In this Scheme example, the [[Function]] `factorial` is tail-recursive, and the Scheme interpreter or compiler would optimize it to avoid growing the [[call]] stack with each recursive [[call]]. --- Bibliography: - [Title - website.com](need%20bibliography.md)