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GitHub - Wilfred/tco.el: Tail call optimisation in Emacs lisp
source link: https://github.com/Wilfred/tco.el
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README.md
tco.el
Tail call optimisation for Emacs lisp
tco.el provides tail-call optimisation for functions in elisp that call themselves in tail-position. Mutually recursive functions are unchanged.
It works by replacing each self-call with a thunk, and wrapping the
function body in a loop that repeatedly evaluates the thunk. Roughly
speaking, a function foo:
(defun-tco foo (...) (...) (foo (...)))
Is rewritten as follows:
(defun foo (...) (flet (foo-thunk (...) (...) (lambda () (foo-thunk (...)))) (let ((result (apply foo-thunk (...)))) (while (functionp result) (setq result (funcall result))) result)))
Example
;; -*- lexical-binding: t -*- (require 'tco) (setq lexical-binding 't) (defun-tco sum (n &optional accum) (setq accum (or accum 0)) (if (zerop n) accum (sum (1- n) (+ accum n)))) ;; Without TCO, values greater than `max-lisp-eval-depth' (usually ;; 600) would cause stack overflow here: (sum 700)
Known issues
Due to a bug in cl-letf in Emacs 24.3.1, this package will not work on Emacs 24.3.1.
Other Projects
recur also offers TCO for self-tail recursion.
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