New IELM option to insert newline when inside sexp (bug#80123)

* lisp/ielm.el (ielm-dynamic-return): Add new value `point' to
user option.
(ielm-return): Implement it (bug#80123).

etc/NEWS

@@ -2060,6 +2060,13 @@ When you kill the IELM process with 'C-c C-c', the input history is now
 saved to the file specified by 'ielm-history-file-name', just like when
 you exit the Emacs session or kill the IELM buffer.
 
+---
+*** New value 'point' for user option 'ielm-dynamic-return'
+When 'ielm-dynamic-return' is set to 'point', typing RET has dynamic
+behavior based on if point is inside an sexp.  While the point is inside
+an sexp typing RET inserts a newline, otherwise the sexp is evaluated.
+This is useful when the mode 'electric-pair-mode' is enabled.
+
 ** DocView
 
 ---

lisp/ielm.el

@@ -97,9 +97,27 @@ customizes `ielm-prompt'.")
 
 (defcustom ielm-dynamic-return t
   "Controls whether \\<ielm-map>\\[ielm-return] has intelligent behavior in IELM.
-If non-nil, \\[ielm-return] evaluates input for complete sexps, or inserts a newline
-and indents for incomplete sexps.  If nil, always inserts newlines."
-  :type 'boolean)
+
+If nil, always insert newlines.
+
+If `point', insert newline if the point is in the middle of an sexp,
+otherwise evaluate input.  This is useful if you have
+`electric-pair-mode' enabled.
+
+If any other non-nil value, insert newline for incomplete sexp input and
+evaluate input for complete sexps.  This is similar to the behavior in
+text shells."
+  :type
+  '(radio
+    (const :tag "Always insert newline" nil)
+    (const
+     :tag
+     "Insert newline if point is in middle of sexp, otherwise evaluate input"
+     point)
+    (const
+     :tag
+     "Insert newline for incomplete sexp, otherwise evaluate input"
+     t)))
 
 (defcustom ielm-dynamic-multiline-inputs t
   "Force multiline inputs to start from column zero?
@@ -248,7 +266,8 @@ simply inserts a newline."
   (if ielm-dynamic-return
       (let ((state
              (save-excursion
-               (end-of-line)
+               (unless (eq ielm-dynamic-return 'point)
+                 (end-of-line))
                (parse-partial-sexp (ielm-pm)
                                    (point)))))
         (if (and (< (car state) 1) (not (nth 3 state)))