Question

I always get error when use flymake-mode. And flymake-mode turn off.

So I want to check whether flymake-mode is on. If it is not on, I will turn it on before call flymake-next-error.

Thanks.

Answer 1

Most minor modes are defined using the define-minor-mode macro. For buffer-local modes, that macro creates a buffer-local variable of the same name as the mode itself¹. The variable is non-nil when the mode is enabled for the current buffer.

Therefore to check whether flymake-mode is enabled, you can test the variable flymake-mode (noting that this variable might not be defined at all if the mode has not been enabled):

(and (boundp 'flymake-mode) flymake-mode)

Which, as Thom point out in the comments, can be expressed using the convenient macro:

(bound-and-true-p flymake-mode)

Which we can use as the condition for an if or when or unless expression:

(if (bound-and-true-p flymake-mode)
    (message "flymake-mode is on")
  (message "flymake-mode is off"))

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¹ For global minor modes, the corresponding variable is global; but flymake-mode is buffer-local.