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elispemacs24

Try-catch and print trace in elisp

How can this javascript code sample for throw/catch error written using elisp?

throw new Error("Boom!!!")
catch(error){
    console.log(err.stack)
}
Solution

  • Emacs Lisp distinguishes between conditions, a high-level object-oriented construct, and non-local exits, a low-level construct that allows exiting a scope prematurely.

    Conditions are captured using condition-case:

    (condition-case nil
    (error "Error!")
  (error (message "Caught error")))

    Non-local exists are handled using catch:

    (progn
  (catch 'catcher
    (throw 'catcher 42))
  (message "Caught .. or perhaps not"))

    In general, you should use conditions if you wish to participate in Emacs' error handling protocols, and catch/throw if you only need to exit prematurely.

    In order to compute a backtrace, you may use the function backtrace:

    (catch 'catcher
  (throw 'catcher
    (with-temp-buffer
      (backtrace)
      (buffer-string))))