branch: externals/denote-sequence
commit 3c0d4b6d0dd4db34b6ab729f2cfe48d62fa027e6
Author: Protesilaos Stavrou <i...@protesilaos.com>
Commit: Protesilaos Stavrou <i...@protesilaos.com>
Define denote-sequence-decrement function
---
denote-sequence.el | 28 ++++++++++++++++++++++++++++
1 file changed, 28 insertions(+)
diff --git a/denote-sequence.el b/denote-sequence.el
index abc572aa75..1d0783ec45 100644
--- a/denote-sequence.el
+++ b/denote-sequence.el
@@ -314,6 +314,34 @@ STRING is part of a sequence, not the entirety of it."
(apply #'concat
(append (butlast letters)
(list (char-to-string (+ (string-to-char last)
1))))))))))
+
+(defun denote-sequence-decrement (string)
+ "Decrement number represented by STRING and return it as a string.
+STRING is part of a sequence, not the entirety of it.
+
+Also see `denote-sequence-increment'."
+ (cond
+ ((denote-sequence--numeric-partial-p string)
+ (let ((number (string-to-number string)))
+ (unless (= number 1)
+ (number-to-string (- number 1)))))
+ ((denote-sequence--alphanumeric-partial-p string)
+ (let* ((letters (split-string string "" :omit-nulls))
+ (length-1-p (= (length letters) 1))
+ (first (car letters))
+ (reverse (nreverse (copy-sequence letters)))
+ (last (car reverse)))
+ (cond
+ ((and length-1-p (string= "a" first))
+ nil)
+ (length-1-p
+ (char-to-string (- (string-to-char first) 1)))
+ ((string= "a" last)
+ (apply #'concat (butlast letters)))
+ (t
+ (apply #'concat
+ (append (butlast letters)
+ (list (char-to-string (- (string-to-char last)
1)))))))))
(t
(error "The string `%s' must contain only numbers or letters" string))))
