Problems with an OrIfPlain type definition

[Barrie Stott]

I have the following in a setup file.

def @LetterType { ch }
def @OrIfch
        precedence 80
        left x
        right y
{
        @LetterType @Case {
                me @Yield x
                ch @Yield y
    }
}

and I use it as in

@Use { @DocumentSetup
        @StartOddFoot { @Null @OrIfch { /1c }}}

This seems to select things properly but if I use `/1c' instead of `{ /1c }'
it is useless, behaving as though I had used

        @StartOddFoot { /1c }

Why?

A more general question is: what can replace x and y in OrIfch? The following
snippet works as I expect and it can be seen to have the same structure as the
body of @OrIfch. However, if I recast it to use @OrIfch, it seems to give
something akin to both x and y.

@LetterType @Case {
        me @Yield {
                @FourThings
                        upperright
                                {                       9 Bankfield
                                        /1vo  Westhoughton
                                        /1vo    Bolton   BL5  2QG
                                        /1vo    Tel: 01942  817892
                                        /1vo    @I -2p @Font { address@hidden }
                                }
                        lowerright { @Date }
                //2v
                @B @To
        }
        ch @Yield {
                @Place address@hidden 
"/home/gbs/mytex/church/letters/chletterhead.epsf.gz"}
                //80pu
                @RightDisplay { @Date @TL }
                @LLP @B @To
        }}

Any help, to get me further up the lout learning curve, would be much
appreciated.

Barrie.