feat(reader): set previous attribute on form for easy traversal

Author: Fuco1

elsa-form.el

@@ -15,7 +15,14 @@
    (type :type elsa-type :initarg :type :initform (elsa-type-mixed))
    (narrow-types :initarg :narrow-type :initform nil)
    (reachable :type trinary :initarg :reachable :initform (trinary-true))
-   (parent :type (or elsa-form nil) :initarg :parent)
+   (parent
+    :type (or elsa-form null)
+    :initarg :parent
+    :documentation "Parent form.")
+   (previous
+    :type (or elsa-form null)
+    :initarg :previous
+    :documentation "Previous form in a sequence.")
    (annotation :type list :initarg :annotation :initform nil))
   :abstract t)
 

elsa-reader.el

@@ -656,17 +656,27 @@ for the analysis."
            (let ((cons-form (cond
                              ((elsa--quote-p (car form))
                               (elsa--read-quote form state))
-                             (t (elsa--read-cons form state)))))
+                             (t (elsa--read-cons form state))))
+                 (previous nil))
              (elsa-form-foreach cons-form
-               (lambda (f) (oset f parent cons-form)))
+               (lambda (f)
+                 (oset f parent cons-form)
+                 ;; first one is set to nil
+                 (oset f previous previous)
+                 (setq previous f)))
              cons-form))
           ((integerp form) (elsa--read-integer form))
           ((floatp form) (elsa--read-float form))
           ((stringp form) (elsa--read-string form))
           ((vectorp form)
-           (let ((vector-form (elsa--read-vector form state)))
+           (let ((vector-form (elsa--read-vector form state))
+                 (previous nil))
              (elsa-form-foreach vector-form
-               (lambda (f) (oset f parent vector-form)))
+               (lambda (f)
+                 (oset f parent vector-form)
+                 ;; first one is set to nil
+                 (oset f previous previous)
+                 (setq previous f)))
              vector-form))
           ((functionp form) (elsa--read-function form state))
           (t (error "Invalid form")))))

tests/test-reader.el

@@ -153,8 +153,23 @@
       (it "should read a list in dotted notation with quoted last cdr"
         (elsa-test-with-read-form "(foo . (quote . '(bar baz)))" form
           (expect (elsa-form-list-p form) :to-be-truthy)
-          (expect (elsa-form-print form) :to-equal "(foo quote quote (bar baz))")))))
+          (expect (elsa-form-print form) :to-equal "(foo quote quote (bar baz))"))))
 
+    (describe "setting parents"
+
+      (it "should set parent of forms in a list to the list form"
+        (elsa-test-with-read-form "(a b c)" form
+          (expect (oref (elsa-nth 0 form) parent) :to-be form)
+          (expect (oref (elsa-nth 1 form) parent) :to-be form)
+          (expect (oref (elsa-nth 2 form) parent) :to-be form))))
+
+    (describe "setting previous"
+
+      (it "should set previous of forms in a list to the previous form"
+        (elsa-test-with-read-form "(a b c)" form
+          (expect (oref (elsa-nth 0 form) previous) :to-be nil)
+          (expect (oref (elsa-nth 1 form) previous) :to-be (elsa-nth 0 form))
+          (expect (oref (elsa-nth 2 form) previous) :to-be (elsa-nth 1 form))))))
 
   (describe "functions"