[Jprogramming] Innovation in the core language

All, As you're all aware, I no longer contribute to the Forums (though I would if there were some interface other than email), but I do track the messages from time to time, and I check out the wiki for information about new releases and changes. I am sending this because I very much want and ne

[Jprogramming] Old trace function

Many years ago (J4 or J6) I remember there was a function that showed how hooks and trains etc were expanded, using such output as x _f_ g_ y etc (where _f_ indicated dyad etc). Does anyone know of this and whether it still exists? Thanks in advance --