flex Expert System Toolkit - LPIS

7. Knowledge Specification Language 99
flex toolkit
to slots or modify the facts / exceptions in the database.
Its use is similar to a data statement in establishing the initial state of some
problem, but, unlike data, anything executed by a do statement in this way
is not re-established by the flex routine restart/1. A do statement is for
executing directives once at compile time, and once only.
The general format of a do statement is as follows.
do directive(s) .
Examples
do the contents of jugA become 2
and jugB`s contents become jugB`s capacity - 2
and remember that danger_level( yellow ) .
do c1 is a new car whose engine_size is 1100
and c1`s model := 'Whizzo'
and c1`s colour := metallic_blue .
To illustrate the difference between do and data, consider the following
example.
frame widget
default screws is 0 and
default bolts is 0.
relation get_widget( W, S, B )
if W is some widget
whose screws is S and whose bolts is B.
do w1 is a new widget
whose screws is 50 and whose bolts is 10.
data new_widgets
do w2 is a new widget
whose screws is 20 and whose bolts is 30.
We may find the current instances of widget using the query
get_widget/3. Initially after compilation, there will be two widgets, w1
and w2, as declared by the data and do statements above.
?- get_widget( W, S, B ).
W = w1, S = 50, B = 10
W = w2, S = 20, B = 30
However, if we precede the query with the flex call to restart/0, which
reinitialises the flex workspace, we will see that the widget w2 is restored (as
in the data statement) but the widget w1 is not restored (because it was only
declared in a do statement).
?- restart, get_widget( W, S, B ).
W = w2, S = 20, B = 30