OpenEuphoria

1. Unknown as a legal var state?

• Posted by Rom <kjehas at frisurf.no> Nov 23, 2002
• 508 views

From: "Juergen Luethje" <jluethje at gmx.de>

> The above mentioned use of "nil" is primarily independent of the =
problem
> of uninstanciated variables, and those things shouldn't be mixed up, I
> think. Using nil for such variables looks easy indeed, but I think =
it's
> also easy to genarate a runtime error (as Euphoria currently does), to
> deal with them. The question is to me, what brings more benefit?


I feel it would be a great help. I cannot prove that of course, but I =
can give you arguments. Look at the example below and try to figure out =
how to formulate (N and U and I) as a rule when you are not allowed to =
deal with  unknown states. It becomes very tricky.

On the other hand, if a program has a state for unknown it almost =
immediate appears be be smart to the user, giving respons like:

"A cannot answer your question .... Because I don't know your user ID"

"Response: You are a girl -> yes. Your  are a student -> no. You have a =
boyfried -> I don't know. You should go on vacation -> I don't know"

The power of just 8-10  3-state-logic rules is good enough to represent =
the basic legislation about unemployment rules (I did that with =
certainty factors ... but that isn't really the right =
tool.....3-state-logic is the rigth tool for dealing with exact rules).


Rom


Example case:=20
Simplified rules for unemployments benefits. How to program such rules?

To qualify for unemployment benefits....
1) you must be a national citizen
2) you must be unemployed
3) you must have earned more than $10000 previous year
4) all facts must be documented


The following program produces too many rejections, leading to a row of
complains......

boolean N, U, I
/*
N =3D person is a national citizen
U =3D person is unemployed
I =3D income previous year was > 10000
*/

// Facts
N =3D True
U =3D True
I =3D False // meaning income was < 10000 or documentation was not =
submitted

    if N and U and I then
        printf( "Accept application")
    else
        printf( "Reject application")
    end if


The following program produces too many inquiries about documentation. =
Many og these enquiries for more documentation is unnecessary for making =
a decision=20
(you may compare this solution to what will happen if you are forced to =
instanciate all vars)

boolean N, U, I
boolean NDocOK, UDocOK, IDocOK

// Facts
N =3D True
NDocOK =3D True
U =3D True
UDocOK =3D True // unemployment status is verified
I =3D True
IDocOK =3D False // documentation of income is missing

    if not( NDocOK and UDocOK oand IDocOK) then
        printf( "Ask for more documentation")
        EXIT
    end if

    if N and U and I then
        printf( "Accept application")
    else
        printf( "Reject application")
    end if


This is another attempt to program the rules, not 100% right

    if N and U and I then
    if NDocOK and UDocOK and IDocOK then
        -- Accept application
    else
        -- Ask for documentation
    else
        if (N xor NDocOK) or (U xor UDocOK) or (I xor IDocOK) then
            -- Ask for clarification
        else
            -- Reject application
    end if;