Search in readable eww buffer [duplicate]

Question

I would like to open url in eww in readable-mode and find str. Below is my code that doesn't work:

(defun my-eww-searh-readable (str)
  "Once-off call to `my-eww-searh-readable' after EWW is done rendering."
  (unwind-protect
      (eww-readable)
    (search-forward-regexp str)
    (remove-hook 'eww-after-render-hook (lambda () (my-eww-searh-readable str)))))

(defun my-eww-url (url str)
  "Open URL in `eww' with `eww-readable' enabled and search str."
  (interactive)
  (add-hook 'eww-after-render-hook (lambda () (my-eww-searh-readable str)))
  (eww url))

(setq strtmp "eww")
(setq ulr "https://emacs.stackexchange.com/questions/50807/search-in-readable-eww-buffer")
(my-eww-url url strtmp)

I found the following mistake:

Symbol’s value as variable is void: str

What do I do wrong?

Answer 1

You seem to be using dynamic binding which means that str would be evaluated once your lambda function is executed at which time the variable str is no longer in scope.

You should turn on lexical binding to have your hook function converted into a closure during the invocation of my-eww-url so that once your hook function will be invoked str will be bound to the same variable it was when my-eww-url was invoked. You can turn on lexical binding by putting ;;; -*- lexical-binding: t; -*- in the first line of your file.

Note that with lexical binding your approach for removing the hook again in my-eww-searh-readable will no longer work as the closure created in my-eww-searh-readable will differ from the one previously created in my-eww-url. In your situation using (remove-hook 'eww-after-render-hook (first eww-after-render-hook)) instead should suffice.

If for some reason you cannot or do not want to use lexical binding you can have the variable str evaluated when adding (and removing) the hook function by using backquotes with commas as follows:

(defun my-eww-searh-readable (str)
  "Once-off call to `my-eww-searh-readable' after EWW is done rendering."
  (unwind-protect
      (eww-readable)
    (search-forward-regexp str)
    (remove-hook 'eww-after-render-hook `(lambda () (my-eww-searh-readable ,str)))))

(defun my-eww-url (url str)
  "Open URL in `eww' with `eww-readable' enabled and search str."
  (interactive)
  (add-hook 'eww-after-render-hook `(lambda () (my-eww-searh-readable ,str)))
  (eww url))

For more background also refer to (elisp)Variable Scoping and to the answer to Scope in lambda.