call error("in omatch: can't happen"); - Line from omatch routine on pg. 146 [1]. Snips from discussion in [1]: "We can expect problems, therefore, and shou

call error("in omatch: can't happen"); - Line from omatch routine on pg. 146 [1]. Snips from discussion in [1]: "We can expect problems, therefore, and should prepare for them. ... Garbage is bad enough, but garbage which is expected to contain a count to tell you how long it is can be much worse. ... The first time we ran this code it said 'can't happen' We got that message perhaps a hundred times in the process of adding the rest of the code... This experience speaks for itself; if you're going to walk a high-wire, use a net." 'Can't happen' is as much a pattern as 'Hello, World'... and it has the same genesis. [1] Brian Kernighan, P.J. Plauger, 'Software Tools', Addison-Wesley 1976