Fix bug: incorrect assumption of mutability.

diff --git a/src/runtime/dbgutl.scm b/src/runtime/dbgutl.scm
index 50e6512ab2da182d88911e473c298333f34f5d89..2edadb2ba9468d45d460116afe8edbc6e961ca3f 100644 (file)
--- a/src/runtime/dbgutl.scm
+++ b/src/runtime/dbgutl.scm
@@ -94,8 +94,9 @@ USA.
               (parameterize* (list (cons current-output-port port))
                              thunk)))))
       (if (and (car x) (> length 4))
-         (string-copy! (cdr x) (- length 4) " ..."))
-      (cdr x))))
+         (string-append (string-slice (cdr x) 0 (- length 4))
+                        " ...")
+         (cdr x)))))
 
 (define (show-frames environment depth port)
   (debugger-presentation port