There are four functions
istrue
isfalse
isnottrue
isnotfalse
defined in bool.c and exported to SQL that are not documented anywhere
and are not part of any spec that I would know of. The release notes
indicate that they were used to implement IS TRUE, IS FALSE, etc. until
PostgreSQL 6.2, so they were internal functions from the very beginning. Should we remove those now? I suppose there
isa slight chance that
10 year old dumps might contain references to them? But it is easy to
reimplement them in user-space should anyone need them.
