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diff --git a/users/aspen/emacs.d/splitjoin.el b/users/aspen/emacs.d/splitjoin.el
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+;;; -*- lexical-binding: t; -*-
+
+(require 'dash)
+(load! "utils")
+
+;;;
+;;; Vars
+;;;
+
+(defvar +splitjoin/split-callbacks '()
+  "Alist mapping major mode symbol names to lists of split callbacks")
+
+(defvar +splitjoin/join-callbacks '()
+  "Alist mapping major mode symbol names to lists of join callbacks")
+
+
+
+;;;
+;;; Definition macros
+;;;
+
+(defmacro +splitjoin/defsplit (mode name &rest body)
+  `(setf
+    (alist-get ',name (alist-get ,mode +splitjoin/split-callbacks))
+    (λ! () ,@body)))
+
+(defmacro +splitjoin/defjoin (mode name &rest body)
+  `(setf
+    (alist-get ',name (alist-get ,mode +splitjoin/join-callbacks))
+    (λ! () ,@body)))
+
+;;;
+;;; Commands
+;;;
+
+(defun +splitjoin/split ()
+  (interactive)
+  (when-let (callbacks (->> +splitjoin/split-callbacks
+                            (alist-get major-mode)
+                            (-map #'cdr)))
+    (find-if #'funcall callbacks)))
+
+(defun +splitjoin/join ()
+  (interactive)
+  (when-let (callbacks (->> +splitjoin/join-callbacks
+                            (alist-get major-mode)
+                            (-map #'cdr)))
+    (find-if #'funcall callbacks)))
+
+
+;;;
+;;; Splits and joins
+;;; TODO: this should probably go in a file-per-language
+;;;
+
+(+splitjoin/defjoin
+ 'elixir-mode
+ join-do
+ (let* ((function-pattern (rx (and (zero-or-more whitespace)
+                                   "do"
+                                   (zero-or-more whitespace)
+                                   (optional (and "#" (zero-or-more anything)))
+                                   eol)))
+        (end-pattern (rx bol
+                         (zero-or-more whitespace)
+                         "end"
+                         (zero-or-more whitespace)
+                         eol))
+        (else-pattern (rx bol
+                         (zero-or-more whitespace)
+                         "else"
+                         (zero-or-more whitespace)
+                         eol))
+        (lineno     (line-number-at-pos))
+        (line       (thing-at-point 'line t)))
+   (when-let ((do-start-pos (string-match function-pattern line)))
+     (cond
+      ((string-match-p end-pattern (get-line (inc lineno)))
+       (modify-then-indent
+        (goto-line-char do-start-pos)
+        (insert ",")
+        (goto-char (line-end-position))
+        (insert ": nil")
+        (line-move 1)
+        (delete-line))
+       t)
+
+      ((string-match-p end-pattern (get-line (+ 2 lineno)))
+       (modify-then-indent
+        (goto-line-char do-start-pos)
+        (insert ",")
+        (goto-char (line-end-position))
+        (insert ":")
+        (join-line t)
+        (line-move 1)
+        (delete-line))
+       t)
+
+      ((and (string-match-p else-pattern (get-line (+ 2 lineno)))
+            (string-match-p end-pattern  (get-line (+ 4 lineno))))
+       (modify-then-indent
+        (goto-line-char do-start-pos)
+        (insert ",")
+        (goto-char (line-end-position))
+        (insert ":")
+        (join-line t)
+        (goto-eol)
+        (insert ",")
+        (join-line t)
+        (goto-eol)
+        (insert ":")
+        (join-line t)
+        (line-move 1)
+        (delete-line))
+       t)))))
+
+(comment
+ (string-match (rx (and bol
+                        "if "
+                        (one-or-more anything)
+                        ","
+                        (zero-or-more whitespace)
+                        "do:"
+                        (one-or-more anything)
+                        ","
+                        (zero-or-more whitespace)
+                        "else:"
+                        (one-or-more anything)))
+               "if 1, do: nil, else: nil")
+
+ )
+
+(+splitjoin/defsplit
+ 'elixir-mode
+ split-do-with-optional-else
+ (let* ((if-with-else-pattern (rx (and bol
+                                       (one-or-more anything)
+                                       ","
+                                       (zero-or-more whitespace)
+                                       "do:"
+                                       (one-or-more anything)
+                                       (optional
+                                        ","
+                                        (zero-or-more whitespace)
+                                        "else:"
+                                        (one-or-more anything)))))
+        (current-line (get-line)))
+   (when (string-match if-with-else-pattern current-line)
+     (modify-then-indent
+      (assert (goto-regex-on-line ",[[:space:]]*do:"))
+      (delete-char 1)
+      (assert (goto-regex-on-line ":"))
+      (delete-char 1)
+      (insert "\n")
+      (when (goto-regex-on-line-r ",[[:space:]]*else:")
+        (delete-char 1)
+        (insert "\n")
+        (assert (goto-regex-on-line ":"))
+        (delete-char 1)
+        (insert "\n"))
+      (goto-eol)
+      (insert "\nend"))
+     t)))
+
+(comment
+ (+splitjoin/defsplit 'elixir-mode split-def
+ (let ((function-pattern (rx (and ","
+                                  (zero-or-more whitespace)
+                                  "do:")))
+       (line (thing-at-point 'line t)))
+   (when-let (idx (string-match function-pattern line))
+     (let ((beg (line-beginning-position))
+           (orig-line-char (- (point) (line-beginning-position))))
+       (save-mark-and-excursion
+        (goto-line-char idx)
+        (delete-char 1)
+        (goto-line-char (string-match ":" (thing-at-point 'line t)))
+        (delete-char 1)
+        (insert "\n")
+        (goto-eol)
+        (insert "\n")
+        (insert "end")
+        (evil-indent beg (+ (line-end-position) 1))))
+     (goto-line-char orig-line-char)
+     t))))
+
+(+splitjoin/defjoin
+ 'elixir-mode
+ join-if-with-else
+ (let* ((current-line (thing-at-point 'line)))))
+
+(provide 'splitjoin)