In ML, the If construct has several forms permitting the expression of loops.

The basic form is

if <ml> then <ml> else <ml>

which can be inserted in ML mode with the `if' command; insertion of the current point term is either into the Then part or the Else part, depending on the setting of the left/right-mode.

The variant forms are not essential, but are edited as follows.

If the If form is nested through the Else place, then the "else" particle can be toggled with the `(backspace)' command. Toggling like this if the Else place is empty will insert another If form before removing the "else" particle.

The presence of the "else" particle becomes significant only in order to determine the scope of a loop construct. The basic form can be toggled with loop forms thus:

if <ml> loop <ml> else <ml>
if <ml> then <ml> loop <ml>
if <ml> loop <ml> loop <ml>

are variants indicating when looping will occur from the branches.
In normal left-to-right mode, `(c-a)(c-(backspace))' toggles the then/loop particle, while in right-to-left mode, it toggles the else/loop particle. IF YOU CAN SEE THIS go to /sfa/Nuprl/Shared/Xindentation_hack_doc.html