flex Expert System Toolkit - LPIS

7. Knowledge Specification Language 105
Templates
synonym weight_calc
its volume times its density .
All occurrences of weight_calc will be replaced by the term its
volume times its density.
synonym interest_rate 8.5 .
All occurrences of interest_rate will be replaced by the number 8.5.
Here, if the interest rate changes, only one change is necessary (to the
synonym definition) before recompiling source code.
Like a synonym, a template assists the readability of KSL statements. A
template can be thought of as a parameterised synonym, allowing textual
replacements at compile-time. The ^ symbol is used to indicate an argument
position.
A template may have a positive form and an optional negative form. The
basic format of a template is:
template replacement
positive_template ;
negative_template .
At compile time, any terms of the form positive_template will be
replaced by replacement, and any terms of the form
negative_template will be replaced by not replacement, with
arguments being replaced appropriately. Often the replacement term will
be defined as a relation or an action.
For example, suppose we have the following template (which only has a
positive form).
template empty_out
empty out ^ .
Then in KSL source code the expression
empty out jug1
will be converted at compile time to
empty_out( jug1 )
We may define the action empty_out/1, also making use of the template,
as follows.
action empty out X ;
do X`s contents becomes 0 .
flex toolkit