Add prescient-aggressive-file-save (#39)

CHANGELOG.md

@@ -3,6 +3,15 @@
 All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog].
 
+## Unreleased
+### Enhancements
+* New user option `prescient-aggressive-file-save` to enable
+  saving the cache data more aggressively according to the
+  discussions ([#17] and [#39]).
+
+[#17]: https://github.com/raxod502/prescient.el/issues/17
+[#39]: https://github.com/raxod502/prescient.el/pull/39
+
 ## 3.2 (released 2019-07-06)
 ### New features
 * New user options `prescient-sort-length-enable` and

prescient.el

@@ -123,6 +123,13 @@ usefully be sorted by length (presumably, the backend returns
 these results in some already-sorted order)."
   :type 'boolean)
 
+(defcustom prescient-aggressive-file-save nil
+  "Whether to save the cache file aggressively.
+If non-nil, then write the cache data to `prescient-save-file'
+after the cache data is updated by `prescient-remember' when
+`prescient-persist-mode' is activated."
+  :type 'boolean)
+
 ;;;; Caches
 
 (defvar prescient--history (make-hash-table :test 'equal)
@@ -457,7 +464,11 @@ Return the sorted list. The original is modified destructively."
                  (puthash cand new-freq prescient--frequency))))
            prescient--frequency)
   ;; Update serial number.
-  (cl-incf prescient--serial-number))
+  (cl-incf prescient--serial-number)
+  ;; Save the cache data.
+  (when (and prescient-persist-mode
+	     prescient-aggressive-file-save)
+    (prescient--save)))
 
 ;;;; Closing remarks