# 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]].
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Bibliography:
- [Title - website.com](need%20bibliography.md)