flex Expert System Toolkit - LPIS

7. Knowledge Specification Language 78
The basic format of a repeat-until loop is:
repeat directive(s)
until condition(s)
end repeat
Example
The following action repeatedly adds one to the current value of the up
attribute of count and subtracts one from the current value of the down
attribute of count until the up value is greater than or equal to the down
value.
action balance ;
do repeat add 1 to the up of count
and subtract 1 from the down of count
until the up of count >= down of count
end repeat
and write( 'Balance ' )
and write( up of count ) and tab( 1 )
and write( down of count ) and nl .
Note the use of the built-in Prolog predicates write/1, tab/1 and nl/0.
Recall that the increment and decrement operators, add and subtract,
only increment and decrement the current values of attributes. If there is no
current value the directive subtract will fail. In the case of the add
directive, if there is no current value the increment will be assigned to the
current value of the slot.
While-Do Loops
While loops repeat the given directive while a condition holds. The directive
is performed after the test is made. The basic format of a while-do loop is
as follows.
while condition(s)
do directive(s)
end while
Example
The following action would be used to remove from the customer loan
records of a bank all instances of customer whose loan has been repaid.
action remove_paid_customer ;
do while Customer is some customer
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