A THEN or an ELSE clause was found that does not match a
corresponding IF or WHEN clause. This often occurs because of a
missing END or DO...END in the THEN part of a complex IF...THEN...ELSE
block. For example:
WRONG RIGHT
if a = b then do if a = b then do
say "equals" say "equals"
exit exit
else end
say "not equals" else
say "not equals"
