wilfred / loop.el

friendly imperative loop structures for Emacs lisp

loop.el --- friendly imperative loop structures for Emacs lisp

Emacs lisp is missing loop structures familiar to users of newer languages. This library adds a selection of popular loop structures as well as break and continue.

loop.el also has full unit tests.

Table of Contents

• loop.el --- friendly imperative loop structures for Emacs lisp
  • Contents
    • loop-while
    • loop-do-while
    • loop-until
    • loop-for-each
    • loop-for-each-line
    • loop-break
    • loop-continue
  • Alternatives
  • Changelog
  • Running the tests

Contents

loop-while

Repeatedly evaluate BODY while CONDITION is non-nil.

loop-while (condition body...)

Example:

(let ((x 0)
      (sum 0))
  ;; sum the numbers 0 to 9
  (loop-while (< x 10)
    (setq sum (+ sum x))
    (setq x (1+ x))))

loop-do-while

Evaluate BODY, then repeatedly BODY while CONDITION is non-nil.

loop-do-while (condition body...)

Example:

(let ((x 0)
      (sum 0))
  ;; our condition is false on the first iteration
  (loop-do-while (and (> x 0) (< x 10))
    (setq sum (+ sum x))
    (setq x (1+ x))))

loop-until

Repeatedly evaluate BODY until CONDITION is non-nil.

loop-until (condition body...)

Example:

(let ((x 0)
      (sum 0))
  ;; sum the numbers 0 to 9
  (loop-until (= x 10)
    (setq sum (+ sum x))
    (setq x (1+ x))))

loop-for-each

For every item in LIST, evaluate BODY with VAR bound to that item.

• loop-for-each (var list body...)

Example:

(let ((sum 0))
  (loop-for-each x (list 1 2 3 4 5 6 7 8 9)
    (setq sum (+ sum x))))

loop-for-each-line

For every line in the buffer, put point at the start of the line and execute BODY.

• loop-for-each-loop (body...)

Example:

;; Count headings in a markdown buffer.
(let ((heading-count 0))
  (loop-for-each-line
    (when (looking-at "#")
      (setq heading-count (+ heading 1))))

loop-break

Terminate evaluation of a loop-while, loop-do-while, loop-for-each, or loop-for-each-line block. If there are nested loops, breaks out of the innermost loop.

loop-break ()

Example:

(let ((sum 0))
  ;; sum the numbers 1 to 5
  (loop-for-each x (list 1 2 3 4 5 6 7 8 9)
    (setq sum (+ sum x))
    (when (= x 5)
      (loop-break)))
  sum)

loop-continue

Skip the rest of the current loop-while, loop-do-while, or loop-for-each block and continue to the next iteration. If there are nested loops, applies to the innermost loop.

loop-continue ()

Example:

(let ((sum 0))
  ;; sum the numbers 1, 3, 4, 5
  (loop-for-each x (list 1 2 3 4 5)
    (when (= x 2)
      (loop-continue))
    (setq sum (+ sum x))))

Alternatives

• while and dolist are built-in loop structures
• The cl-loop macro in cl-lib
• -each in dash.el

Changelog

• v1.3 loop-for-each-line now works even if point moves around. Inside loop-for-each-line, it is now set to the current line. Added loop-return.
• v1.2 Added loop-for-each-line. Also added edebug support, so you can step through loops in loop.el.
• v1.1 Added loop-continue
• v1.0 loop-for-each now takes three arguments: (VAR LIST BODY...)
• v0.3 Added loop-until
• v0.2 Basic working implementation

Running the tests

M-x loop-run-tests