in-line trap ?

[Matt Wette]

I have been going through the debugging infrastructure and can’t figure out how 
to code in a trap.  I would like something like

(define (xxx) … (if cond (trap-here)) ….)

that would dump me into the interactive debugger when I hit that condition.  
Any help on achieving this is will be appreciated.

I use this a lot in python:
#!/usr/bin/python

import pdb

def xxx:
    …
    if cond:
        pdb.set_trace()
    ….


Matt