Support function as the value of prescient-filter-method (#110)

* Support function as the value of prescient-filter-method

Fixes #83

* Handle prescient-filter-method function when toggling with selectrum

* Update CHANGELOG.md

Co-authored-by: Radon Rosborough <[email protected]>

CHANGELOG.md

@@ -35,6 +35,8 @@ The format is based on [Keep a Changelog].
   will immediately forget a candidate ([#109]).
 
 ### Enhancements
+* `prescient-filter-method` accepts a function which returns the
+  desired filter methods ([#110]).
 * `selectrum-prescient.el`: Match faces are now combined with faces
   that might be already present on candidates instead of replacing
   them which gives better visual results in these cases ([#101],
@@ -66,6 +68,7 @@ The format is based on [Keep a Changelog].
 [#105]: https://github.com/raxod502/prescient.el/pull/105
 [#106]: https://github.com/raxod502/prescient.el/pull/106
 [#109]: https://github.com/raxod502/prescient.el/pull/109
+[#110]: https://github.com/raxod502/prescient.el/pull/110
 
 ## 5.1 (released 2021-02-26)
 ### Enhancements

prescient.el

@@ -116,6 +116,9 @@ is similar to `prefix', but allows for less typing.
 Value can also be a list of any of the above methods, in which
 case each method will be applied in order until one matches.
 
+Value can also be a function which returns any of the allowable
+values documented above.
+
 For backwards compatibility, the value of this variable can also
 be `literal+initialism', which equivalent to the list (`literal'
 `initialism')."
@@ -561,7 +564,10 @@ enclose literal substrings with capture groups."
                      (message
                       "No function in `prescient-filter-alist' for method: %s"
                       method)))
-                 (pcase prescient-filter-method
+                 (pcase
+                     (if (functionp prescient-filter-method)
+                         (funcall prescient-filter-method)
+                       prescient-filter-method)
                    ;; We support `literal+initialism' for backwards
                    ;; compatibility.
                    (`literal+initialism '(literal initialism))

selectrum-prescient.el

@@ -174,8 +174,14 @@ buffer. It does not affect the default behavior (determined by
              ;; be a list of only one filter type.
              (setq prescient-filter-method '(,filter-type))
 
-           ;; Otherwise, if we need to add or remove from the list,
-           ;; make sure it's actually a list and not just a symbol.
+           ;; Otherwise, if the current setting is a function,
+           ;; evaluate it to get the value.
+           (when (functionp prescient-filter-method)
+             (setq prescient-filter-method
+                   (funcall prescient-filter-method)))
+
+           ;; If we need to add or remove from the list, make sure
+           ;; it's actually a list and not just a symbol.
            (when (symbolp prescient-filter-method)
              (setq prescient-filter-method
                    (list prescient-filter-method)))