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How do I make Emacs give me live feedback on my syntax?

Like, after I finish typing a line of code, how can I make it so that Emacs tells me if that line isn't using correct syntax?

For example, in Eclipse, it'll tell you before you compile when a line is not correct (in Java, at least). How can I mimic that behavior in Java, C, etc. for Emacs?

Thanks!

Running Emacs 24 in Terminal by the way. Installed via HomeBrew on OSX.

  • Typing a line of what? What syntax/language are you using? The question is not very clear. Please specify the behavior you are looking for. – Drew Oct 17 '15 at 22:30
  • I'm sorry, I meant for any language in general. For example, Eclipse does a syntax highlight for Java. (I'm doing C at the moment, but same concept). – CodeSammich Oct 17 '15 at 22:48
  • flycheck.org – mbork Oct 17 '15 at 23:09
  • It's not installing via MELPA. Keeps saying that the .el isn't found – CodeSammich Oct 17 '15 at 23:43
  • Nevermind! It's installed. Not really what it looked like on the website, sadly. – CodeSammich Oct 17 '15 at 23:46
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Emacs has a built-in mode called FlyMake that can do this, provided you have a properly configured makefile. Turn flymake on with M-x flymake-mode. It runs an external command (by default make check-syntax) collects the errors and warnings and highlights the buffer appropriately. It works pretty well for C and with some effort can be configured for other languages.

There is also an external package Flycheck that you can install with M-x package-install flycheck. Turn it on with M-x flycheck-mode. With most languages it Just Works with no further configuration. You may need to install some external tool (for example pylint to check Python code).

  • It's working, but it's not working as it should, in my opinion. It highlights the words so much that I can't even read them properly, in full screen. Also highlights some function names and variable types for who knows why. – CodeSammich Oct 18 '15 at 0:29
  • For flycheck you can customize the faces flycheck-warning and flycheck-error to change the highlighting. There are similar faces for flymake. A description of the error should appear in the minibuffer when you put the cursor over it. – erikstokes Oct 18 '15 at 0:47
  • I enabled flymake, intentionally misspelled a variable, intentionally misspelled a word in a comment. Nothing is highlighted. Any suggestions on how I can even begin to debug this? – par Apr 29 at 10:44

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