Writing a @Bnf enviroment

[Benedikt Grundmann]

Hello Folks,

I want to write a simple bnf syntax diagram layouting command.  I thought of 
something like this:

@Bnf
@Begin
expression := { 
kw if expression kw then
  expression
kw else
  expression
kw end
}
@End @Bnf

Which I wanted to expand into:

@Tbl
  aformat { @Cell A | @Cell B | @Cell C }
@Begin
   @Rowa A { expression } B { := } C { lines @Break {
@B if expression @B then 
  expression
@B else
  expression
@B end
}
}
@End @Tbl

In order to achieve that I wrote this definition:

import @Tbl @BasicSetup
export kw ":=" "||"
def @Bnf
  body x
{
  def kw 
    right k
  { @B k }

  def ":="
    left name
    body b
  { @Rowa A { name } B { ":=" } C { lines @Break b } }

  def "||"
    body b
  { @Rowa A {} B { "|" } C { lines @Break b } }

  @Tbl
    aformat { @Cell A | @Cell B | @Cell C }
  @Begin
     x
  @End @Tbl
}


But unfortunately it does not work :-(  It displays nothing at all.

What did I do wrong?

Cheers and thanks for any help,

Benedikt Grundmann

PS: Yes I know about @SyntaxDiag it's just not what I need.