forth-mode automatically tries to indent lines in a smart way,
whenever you type <TAB> or break a line with C-m.
Simple customization can be achieved by setting `forth-indent-level' and `forth-minor-indent-level' in your .emacs file. For historical reasons gforth.el indents per default by multiples of 4 columns. To use the more traditional 3-column indentation, add the following lines to your .emacs:
(add-hook 'forth-mode-hook (function (lambda () ;; customize variables here: (setq forth-indent-level 3) (setq forth-minor-indent-level 1) )))
If you want indentation to recognize non-default words, customize it by setting `forth-custom-indent-words' in your .emacs. See the docstring of `forth-indent-words' for details (in Emacs, type C-h v forth-indent-words).
To customize indentation in a file-specific manner, set `forth-local-indent-words' in a local-variables section at the end of your source file (see Variables).
0 [IF] Local Variables: forth-local-indent-words: ((("t:") (0 . 2) (0 . 2)) ((";t") (-2 . 0) (0 . -2))) End: [THEN]