Tail calls

When a function is called a new stack frame is created in memory to store the arguments and local variables of the function. If lots of these frames are created during recursion then the program would use a large amount of memory, or even crash the program if some limit is hit.

To avoid this problem Gleam supports tail call optimisation, which allows the stack frame for the current function to be reused if a function call is the last thing the function does, removing the memory cost.

Unoptimised recursive functions can often be rewritten into tail call optimised functions by using an accumulator. An accumulator is a variable that is passed along in addition to the data, similar to a mutable variable in a language with while loops.

Accumulators should be hidden away from the users of your code, they are internal implementation details. To do this write a public function that calls a recursive private function with the initial accumulator value.