syntax table malfunction

Question

my-test.el contains the following:

(defun test01 ()
    "scan for end of entry, trapping error."
    (interactive)
    (condition-case nil
        (setq my-pt (scan-lists (point) 1 0))
        (error (setq my-pt nil)))
    (if my-pt
        (message "my pt is %s" my-pt)
    ;;else
        (message "my pt is nil")))

Line 1: abcdfn(def)ghi
Line 2: abcdfn@{def}ghi

I placed the cursor just before the "(" on Line 1 and then did M-x test01. This worked okay. Trying a similar test on Line 2, with the cursor just before the "{" failed, with a "my pt is nil" message. Experimenting I tried the same test in a my-test.txt file (text major mode instead of emacs-lisp major mode). In the text major mode, both Lines 1 and 2 worked okay.

Researching, I inferred that the syntax table for emacs-lisp major mode must be different from the syntax table for text major mode. However, from the my-test.el local buffer, I executed M-x describe-syntax and found the following lines:

The parent syntax table is:
...
{               (}  which means: open, matches }
}               ){  which means: close, matches {
...

Experimenting, I placed the following line in the my-test.el local buffer, placed the cursor at the end of the modify-syntax-entry command, and then typed C-xC-e to execute the command.

(modify-syntax-entry ?{ "(}")

I then re-executed test01 on Line 2; again it failed with a "my pt is nil" message.

Questions:

1. What syntax table oriented command will permit the test01 function to work correctly on Line 2, within an emacs-lisp major mode local buffer?

2. Once I execute the syntax command from question 1, and find test01 working correctly on Line 2, what corresponding syntax table oriented command should I use to BACK-OUT the change made from the syntax command from question 1?

Answer 1

Your approach almost works, but you can't only modify the syntax for the opening { if you want that to match the closing }, so you need both of:

(modify-syntax-entry ?{ "(}")
(modify-syntax-entry ?} "){")

For the second part of your question, see:

• C-hf with-syntax-table
• C-hig (elisp)Syntax Table Functions

Answer 2

I have verified that phils' answer worked perfectly. Below is my corresponding altered function.

(defun test01 ()
    "scan for end of entry, trapping error."
    (interactive)
    (setq my-syntax-table (make-syntax-table))
    (modify-syntax-entry ?{ "(}" my-syntax-table)
    (modify-syntax-entry ?} "){" my-syntax-table)
    (with-syntax-table my-syntax-table
        (condition-case nil
            (setq my-pt (scan-lists (point) 1 0))
            (error (setq my-pt nil)))
        (if my-pt
            (message "my pt is %s" my-pt)
        ;;else
            (message "my pt is nil")))
    (makunbound 'my-syntax-table))