[A68-MODE][COMMITTED] Font-lock string breaks only within strings

[Jose E. Marchesi]

---
 a68-mode.el | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/a68-mode.el b/a68-mode.el
index 8dbeb47..0a8b269 100644
--- a/a68-mode.el
+++ b/a68-mode.el
@@ -211,12 +211,25 @@
 
 ;;;; Font-lock keywords.
 
+(defun a68--string-matcher (re end)
+  "Search for a regexp within Algol 68 strings."
+  (let (pos (case-fold-search t))
+    (while (and (setq pos (re-search-forward re end t))
+                (not (a68-within-string))))
+    pos))
+
+(defun a68--string-break-matcher (end)
+  (a68--string-matcher "\\('[nrft']\\)\\|\\('(.*?)\\)" end))
+
+(defun a68--bad-string-break-matcher (end)
+  (a68--string-matcher "\\(''\\|[^']\\)\\('[^nrft'(]\\)" end))
+
 (defconst a68-font-lock-keywords-common
   (list
    ;; String breaks.  Apostrophe is not (currently) a worthy character
    ;; out of strings, so for now we can just match it anywhere.
-   '("\\('[nrft']\\)\\|\\('(.*?)\\)" 0 ''a68-string-break-face prepend)
-   '("\\(''\\|[^']\\)\\('[^nrft'(]\\)" 2 ''font-lock-warning-face prepend)
+   '(a68--string-break-matcher 0 ''a68-string-break-face t)
+   '(a68--bad-string-break-matcher 2 ''font-lock-warning-face t)
    ;; Two or more consecutive underscore characters are always
    ;; illegal in this stropping regime.
    (cons "_[_]+" ''font-lock-warning-face))
-- 
2.30.2