avoid allocating a new stack frame for a function because the calling function will simply return the value that it gets from the called function. The most common use is tail-recursion, where a recursive function written to take advantage of tail-call optimization can use constant stack space. - SO

see also

• Why tail-recursive functions are loops - One surprising fact is that we can systematically compile any program so that every call is a tail-call, by completely transforming the program into continuation-passing-style (CPS), this essentially eliminates the stack.

# TCO transformation

# Fibonacci

def fibo(n, a, b)
	 (n > 0) ? fibo(n - 1, b, a + b) : a;       
end

# Ruby Tail Call Optimization?

The Ruby Language Specification doesn’t say anything about TCO. It doesn’t say you have to do it, but it also doesn’t say you can’t do it.

• This is unlike Scheme, where the Language Specification requires that all Implementations must perform TCO.

• But it is also unlike Python, where Guido van Rossum has made it very clear on multiple occasions (the last time just a couple of days ago) that Python Implementations should not perform TCO.

# Tail Calls in C

• Parsing Protobuf at 2+GB/s: How I Learned To Love Tail Calls in C / HN