Simplify purescript-ds-create-imenu-index with hashtable

Makefile

@@ -22,6 +22,7 @@ ELFILES = \
 	purescript-string.el \
 	purescript-unicode-input-method.el \
 	purescript-utils.el \
+	purescript-decl-scan.el \
 	purescript-yas.el
 
 ELCFILES = $(ELFILES:.el=.elc)

purescript-decl-scan.el

@@ -104,6 +104,7 @@
 (require 'syntax)
 (require 'cl-lib)
 (require 'imenu)
+(require 'subr-x)
 
 (defgroup purescript-decl-scan nil
   "PureScript declaration scanning (`imenu' support)."
@@ -453,6 +454,12 @@ positions and the type is one of the symbols \"variable\", \"datatype\",
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 ;; Declaration scanning via `imenu'.
 
+(defmacro purescript-when-let (spec &rest body)
+  "A wrapper to silence `when-let' deprecation warning"
+  (if (fboundp 'when-let*)
+      (list 'when-let* spec (macroexp-progn body))
+    (with-no-warnings (list 'when-let spec (macroexp-progn body)))))
+
 ;;;###autoload
 (defun purescript-ds-create-imenu-index ()
   "Function for finding `imenu' declarations in PureScript mode.
@@ -462,11 +469,7 @@ datatypes) in a PureScript file for the `imenu' package."
   ;; These lists are nested using `(INDEX-TITLE . INDEX-ALIST)'.
   (let* ((bird-literate (purescript-ds-bird-p))
          (index-alist '())
-         (index-class-alist '()) ;; Classes
-         (index-var-alist '())   ;; Variables
-         (index-imp-alist '())   ;; Imports
-         (index-inst-alist '())  ;; Instances
-         (index-type-alist '())  ;; Datatypes
+         (imenu (make-hash-table :test 'equal))
          ;; Variables for showing progress.
          (bufname (buffer-name))
          (divisor-of-progress (max 1 (/ (buffer-size) 100)))
@@ -486,40 +489,25 @@ datatypes) in a PureScript file for the `imenu' package."
                  (name (car name-posns))
                  (posns (cdr name-posns))
                  (start-pos (car posns))
-                 (type (cdr result))
-                 ;; Place `(name . start-pos)' in the correct alist.
-                 (sym (cdr (assq type
-                                 '((variable . index-var-alist)
-                                   (datatype . index-type-alist)
-                                   (class . index-class-alist)
-                                   (import . index-imp-alist)
-                                   (instance . index-inst-alist))))))
-            (set sym (cons (cons name start-pos) (symbol-value sym))))))
+                 (type (cdr result)))
+            (puthash type
+                     (cons (cons name start-pos) (gethash type imenu '()))
+                     imenu))))
     ;; Now sort all the lists, label them, and place them in one list.
     (message "Sorting declarations in %s..." bufname)
-    (when index-type-alist
-      (push (cons "Datatypes"
-                  (sort index-type-alist 'purescript-ds-imenu-label-cmp))
-            index-alist))
-    (when index-inst-alist
-      (push (cons "Instances"
-                  (sort index-inst-alist 'purescript-ds-imenu-label-cmp))
-            index-alist))
-    (when index-imp-alist
-      (push (cons "Imports"
-                  (sort index-imp-alist 'purescript-ds-imenu-label-cmp))
-            index-alist))
-    (when index-class-alist
-      (push (cons "Classes"
-                  (sort index-class-alist 'purescript-ds-imenu-label-cmp))
-            index-alist))
-    (when index-var-alist
+    (dolist (type '((datatype . "Datatypes") (instance . "Instances")
+                    (import   . "Imports")   (class    . "Classes")))
+      (purescript-when-let ((curr-alist (gethash (car type) imenu)))
+        (push (cons (cdr type)
+                    (sort curr-alist 'purescript-ds-imenu-label-cmp))
+              index-alist)))
+    (purescript-when-let ((var-alist (gethash 'variable imenu)))
       (if purescript-decl-scan-bindings-as-variables
           (push (cons "Variables"
-                      (sort index-var-alist 'purescript-ds-imenu-label-cmp))
+                      (sort var-alist 'purescript-ds-imenu-label-cmp))
                 index-alist)
         (setq index-alist (append index-alist
-                                  (sort index-var-alist 'purescript-ds-imenu-label-cmp)))))
+                                  (sort var-alist 'purescript-ds-imenu-label-cmp)))))
     (message "Sorting declarations in %s...done" bufname)
     ;; Return the alist.
     index-alist))