Clean up SCC code

doc/haskell-mode.texi

@@ -278,6 +278,15 @@ and available packages.
 @image{anim/company-mode-import-statement}
 @end ifhtml
 
+@section Profiling and Debugging support
+
+When profiling code with GHC, it is often useful to add
+@uref{https://downloads.haskell.org/~ghc/latest/docs/html/users_guide/profiling.html#cost-centres,
+cost centres} by hand.  These allow finer-grained information about
+program behavior.  @code{haskell-mode} provides the function
+@code{haskell-mode-toggle-scc-at-point} to make this more convenient.
+It will remove an SCC annotation at point if one is present, or add
+one if point is over whitespace.  By default it is bound to @kbd{C-c C-s}.
 
 @node Unicode support
 @chapter Unicode support

haskell-mode.el

@@ -202,6 +202,7 @@ be set to the preferred literate style."
     (define-key map (kbd "C-c C-v") 'haskell-mode-enable-process-minor-mode)
     (define-key map (kbd "C-c C-t") 'haskell-mode-enable-process-minor-mode)
     (define-key map (kbd "C-c C-i") 'haskell-mode-enable-process-minor-mode)
+    (define-key map (kbd "C-c C-s") 'haskell-mode-toggle-scc-at-point)
     map)
   "Keymap used in Haskell mode.")
 
@@ -891,13 +892,15 @@ LOC = (list FILE LINE COL)"
 
 ;; From Bryan O'Sullivan's blog:
 ;; http://www.serpentine.com/blog/2007/10/09/using-emacs-to-insert-scc-annotations-in-haskell-code/
-(defun haskell-mode-insert-scc-at-point ()
-  "Insert an SCC annotation at point."
-  (interactive)
-  (if (or (looking-at "\\b\\|[ \t]\\|$") (and (not (bolp))
-                                              (save-excursion
-                                                (forward-char -1)
-                                                (looking-at "\\b\\|[ \t]"))))
+(defun haskell-mode-try-insert-scc-at-point ()
+  "Try to insert an SCC annotation at point.  Return true if
+successful, nil otherwise."
+  (if (or (looking-at "\\b\\|[ \t]\\|$")
+          ;; Allow SCC if point is on a non-letter with whitespace to the left
+          (and (not (bolp))
+               (save-excursion
+                 (forward-char -1)
+                 (looking-at "[ \t]"))))
       (let ((space-at-point (looking-at "[ \t]")))
         (unless (and (not (bolp)) (save-excursion
                                     (forward-char -1)
@@ -906,13 +909,23 @@ LOC = (list FILE LINE COL)"
         (insert "{-# SCC \"\" #-}")
         (unless space-at-point
           (insert " "))
-        (forward-char (if space-at-point -5 -6)))
-    (error "Not over an area of whitespace")))
+        (forward-char (if space-at-point -5 -6))
+        t )))
 
-;; Also Bryan O'Sullivan's.
-(defun haskell-mode-kill-scc-at-point ()
-  "Kill the SCC annotation at point."
+(defun haskell-mode-insert-scc-at-point ()
+  "Insert an SCC annotation at point."
   (interactive)
+  (if (not (haskell-mode-try-insert-scc-at-point))
+      (error "Not over an area of whitespace")))
+
+(make-obsolete
+ 'haskell-mode-insert-scc-at-point
+ 'haskell-mode-toggle-scc-at-point
+ "2015-11-11")
+
+(defun haskell-mode-try-kill-scc-at-point ()
+  "Try to kill an SCC annotation at point.  Return true if
+successful, nil otherwise."
   (save-excursion
     (let ((old-point (point))
           (scc "\\({-#[ \t]*SCC \"[^\"]*\"[ \t]*#-}\\)[ \t]*"))
@@ -921,8 +934,27 @@ LOC = (list FILE LINE COL)"
       (if (and (looking-at scc)
                (<= (match-beginning 1) old-point)
                (> (match-end 1) old-point))
-          (kill-region (match-beginning 0) (match-end 0))
-        (error "No SCC at point")))))
+          (progn (kill-region (match-beginning 0) (match-end 0))
+                 t)))))
+
+;; Also Bryan O'Sullivan's.
+(defun haskell-mode-kill-scc-at-point ()
+  "Kill the SCC annotation at point."
+  (interactive)
+  (if (not (haskell-mode-try-kill-scc-at-point))
+      (error "No SCC at point")))
+
+(make-obsolete
+ 'haskell-mode-kill-scc-at-point
+ 'haskell-mode-toggle-scc-at-point
+ "2015-11-11")
+
+(defun haskell-mode-toggle-scc-at-point ()
+  "If point is in an SCC annotation, kill the annotation.  Otherwise, try to insert a new annotation."
+  (interactive)
+  (if (not (haskell-mode-try-kill-scc-at-point))
+      (if (not (haskell-mode-try-insert-scc-at-point))
+          (error "Could not insert or remove SCC"))))
 
 (defun haskell-guess-module-name ()
   "Guess the current module name of the buffer."

tests/haskell-mode-tests.el

@@ -170,7 +170,7 @@
   (should (with-temp-buffer
             (haskell-mode)
             (insert "Äöèąċōïá")
-            (string= "Äöèąċōïá" (haskell-ident-at-point)))))            
+            (string= "Äöèąċōïá" (haskell-ident-at-point)))))
 
 (ert-deftest unicode-pos ()
   (should (with-temp-buffer
@@ -385,4 +385,31 @@ Also should respect 10 column fill."
 	      '("-- @| a b c d"
                 "-- e")))
 
+(ert-deftest insert-scc-feasible ()
+  "insert an SCC where it's possible to do so"
+  (should (with-temp-buffer
+            (insert "hello world")
+            (goto-char 6)
+            (haskell-mode-toggle-scc-at-point)
+            (string= "hello {-# SCC \"\" #-} world"
+                     (buffer-substring 1 (point-max))))))
+
+(ert-deftest insert-scc-infeasible ()
+  "insert an SCC where it's not possible to do so"
+  (should-error (with-temp-buffer
+            (insert "hello world")
+            (goto-char 2)
+            (haskell-mode-toggle-scc-at-point)
+            (string= "hello world"
+                     (buffer-substring 1 (point-max))))))
+
+(ert-deftest remove-scc ()
+  "insert an SCC where it's possible to do so"
+  (should (with-temp-buffer
+            (insert "hello {-# SCC \"\" #-} world")
+            (goto-char 10)
+            (haskell-mode-toggle-scc-at-point)
+            (string= "hello world"
+                     (buffer-substring 1 (point-max))))))
+
 (provide 'haskell-mode-tests)