Add a function for registering additional ClojureScript REPL types

Handy for people who're not satisfied with the available defaults.

Author: bbatsov

cider.el

@@ -671,7 +671,7 @@ The supplied string will be wrapped in a do form if needed."
         form
       (format "(do %s)" form))))
 
-(defconst cider-cljs-repl-types
+(defvar cider-cljs-repl-types
   '(("Rhino" "(cemerick.piggieback/cljs-repl (cljs.repl.rhino/repl-env))"
      nil)
     ("Nashorn" "(cemerick.piggieback/cljs-repl (cljs.repl.nashorn/repl-env))"
@@ -693,6 +693,26 @@ REPL to start the ClojureScript REPL and functions to very their requirements.
 
 The form should be either a string or a function producing a string.")
 
+(defun cider-register-cljs-repl-type (name init-form &optional requirements-fn)
+  "Register a new ClojureScript REPL type.
+
+Types are defined by the following:
+
+- NAME - string identifier that will be used to refer to the REPL typel
+- INIT-FORM - string or function (symbol) producing string
+- REQUIREMENTS-FN - function to check whether the REPL can be started.
+This param is optional.
+
+All this function does is modifying `cider-cljs-repl-types'.
+It's intended to be used in your Emacs config."
+  (unless (stringp name)
+    (user-error "The REPL name must be a string"))
+  (unless (or (stringp init-form) (symbolp init-form))
+    (user-error "The init form must be a string or a symbol referring to a function"))
+  (unless (or (null requirements-fn) (symbolp requirements-fn))
+    (user-error "The requirements-fn must be a symbol referring to a function"))
+  (add-to-list 'cider-cljs-repl-types (list name init-form requirements-fn)))
+
 (defcustom cider-default-cljs-repl nil
   "The default ClojureScript REPL to start.