Speeding up debugger check (addresses #64)

Soooo, the long delay experienced when evaluating long string lists in
Guile had nothing to do with the time took by emacs to read the response
from the scheme process; that process is always a breeze, no matter or
its format or number of newlines.  The delay was provoked by an innocent
looking function that scans the received string (which includes a prompt
at the end as an EOT marker) to check whether Guile (or any other
scheme) has just entered the debugger (that's done inside
`geiser-con--connection-update-debugging`).  For some reason,
`string-match` on that kind of string using Guile's regexp for a debug
prompt takes forever.  Instead of trying to optimize the regular
expression, i've just applied it to the *second* line of the received
string, which is the one that contains the response's prompt.

1 files changed, 6 insertions, 8 deletions

diff --git a/elisp/geiser-connection.el b/elisp/geiser-connection.el
index 69dd6a9..e466cd3 100644
--- a/elisp/geiser-connection.el
+++ b/elisp/geiser-connection.el
@@ -156,7 +156,8 @@
 
 (defun geiser-con--has-entered-debugger (con answer)
   (and (not (geiser-con--connection-is-debugging con))
-       (geiser-con--connection-update-debugging con answer)))
+       (let ((p (car (last (split-string answer "\n" t)))))
+         (and p (geiser-con--connection-update-debugging con p)))))
 
 (defun geiser-con--connection-eot-p (con txt)
   (and txt
@@ -201,15 +202,12 @@
         `((error (key . geiser-debugger))
           (output . ,answer))
       (condition-case err
-          (let* ((start (string-match "((\\(?:result)?\\|error\\) " answer))
-                 (form (or (and start (car (read-from-string answer start)))
-                           `((error (key . retort-syntax))
-                             (output . ,answer)))))
-            form)
+          (let ((start (string-match "((\\(?:result)?\\|error\\) " answer)))
+            (or (and start (car (read-from-string answer start)))
+                `((error (key . retort-syntax)) (output . ,answer))))
         (error `((error (key . geiser-con-error))
                  (output . ,(format "%s\n(%s)"
-                                    answer
-                                    (error-message-string err)))))))))
+                                    answer (error-message-string err)))))))))
 
 (defun geiser-con--process-completed-request (req answer)
   (let ((cont (geiser-con--request-continuation req))