Beware of Tabs

Why?

You don't want to have tabs in your frege source code because the visual indentation does not match the indentation the compiler sees. The compiler counts only whitespace characters, hence, 3 tabs are regarded the same indentation as 3 blanks. Mixing tabs and spaces will therefore be a constant source of mysterious errors.

How?

Unfortunately, the tab settings of the standard Eclipse text editor, the IMP editor and the incarnation thereof, the Frege editor, interact in a very mysterious way. The following procedure should get it right.

Turn off tabs for new instances of the IMP editor.

Open Windows -> Preferences -> IMP. Check the Use spaces instead of tabs checkbox. Enter your preferred value for Tab width.

Turn off tabs in the Frege preferences

Open Windows -> Preferences -> Frege. Check the Tabs inserts spaces checkbox. Enter your preferred value for Tabulator Width.

Turn off tabs in the Eclipse editor

In a frege editor window, right click and select Preferences ... in the popup menu. Check the Insert spaces for tabs checkbox. Enter your preferred value for Displayed tab width.