The <condition> element of an IF, UNLESS, WHILE or UNTIL
statement may be any expression. If the expression
evaluates to zero then <condition> is FALSE, otherwise it
is TRUE.

Some example expressions:

$eq(%answer,"Y")
%a >= %b
(%a > 2) & (%a < 9)
$len(%b) = 4

<condition> may also be any of the following BOOLEAN
functions:

(NOT) (UN)CONNECTED

     CONNECTED is TRUE if your modem is currently
     connected or 'talking to' a remote computer.

(NOT) (NO)ERROR

     ERROR is TRUE if an earlier statement failed to
     execute correctly. e.g., when reading a file, ERROR
     will be TRUE if end_of_file has been reached.
     
     Generally, ERROR is set by any command which causes
     disc access. This means GETFIRST and GETNEXT as well
     as the record-level functions like FOPEN, FREAD, etc.

(NOT) (NO)KEYPRESSED

     KEYPRESSED is TRUE if a keyboard key has been pressed
     and is therefore waiting to be read with a GETKEY
     command.

(NOT) EXISTS <wildcard_path_name>

     EXISTS is true if one or more files exist which match
     the DOS wildcard path name.
     
     Note that EXISTS uses the GETFIRST function so calls
     on EXISTS may not be embedded within GETFIRST/GETNEXT
     loops.

(NOT) HAD <1_to_10>

     'HAD n' is TRUE if the most recently executed Wait or
     SendWait command received its n'th string.
     
     e.g. SendWait "fred^M" "ok" "maybe" "not ok"
          IF Had 1
             Message "received 'ok' from remote system"
               
          ElsIf Had 2
             Message "received 'maybe' from remote system"
               
          Else
             Message "received 'not ok' from remote system"
               
          EndIf

     Note that the phrase 'If Had n' is exactly equivalent
     to the phrase 'If %Had=n' (see the section on System
     Constants and Variables).
