In fold-matches, set regexp/notbol unless matching string start.

* module/ice-9/regex.scm (fold-matches): Set regexp/notbol if the
  starting position is nonzero.
* test-suite/tests/regexp.test (fold-matches): Check that when
  matching /^foo/ against "foofoofoofoo", only one match results.

Signed-off-by: Ludovic Courtès <ludo@gnu.org>

module/ice-9/regex.scm

@@ -172,8 +172,9 @@
     (let loop ((start 0)
                (value init)
                (abuts #f))              ; True if start abuts a previous match.
+      (define bol (if (zero? start) 0 regexp/notbol))
       (let ((m (if (> start (string-length string)) #f
-                   (regexp-exec regexp string start flags))))
+                   (regexp-exec regexp string start (logior flags bol)))))
         (cond
          ((not m) value)
          ((and (= (match:start m) (match:end m)) abuts)

test-suite/tests/regexp.test

@@ -132,7 +132,14 @@
                    (lambda (match result)
                      (cons (match:substring match)
                            result))
-                   (logior regexp/notbol regexp/noteol)))))
+                   (logior regexp/notbol regexp/noteol))))
+
+  (pass-if "regexp/notbol is set correctly"
+    (equal? '("foo")
+            (fold-matches "^foo" "foofoofoofoo" '()
+                          (lambda (match result)
+                            (cons (match:substring match)
+                                  result))))))
 
 
 ;;;