OpenEuphoria

Example where Euphoria defaults on a boolean expression

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

You get a phone call from your boss where you are ordered to search for =
information about dyslexia .. immediately! You go to the PC and start =
websearching. In the phone conversation you were told which words to =
search for...... it was "dyslexia"(A) and "adult"(B) and something =
else(C) which you don't remember. What to do when you don't know the =
third search criterium?

In this situation you will probably dismiss C from the rule and state:

 if A and B then match.....

Is this a valid transformation of boolean logic ... when one variable is =
unknown? What this rule returns is not the same as what your boss asked =
you to do.

Any variable may be nil (=3Duninstanciated). That has a lot of =
implications.

 if A and B and C then match....

When A=3DTrue, B=3DTrue and C=3Dnil then this rule CANNOT be solved as =
True or False  (i.e result is nil). That is consistent with boolean =
logic (and any other logic too)=20

Logically you could deduct that the paper you return is:

 not (what he asked for)  and
 not (not (what he asked for))

If E =3D what he asked for then
 not E and not( not E)   =3D>   not E and E  =3D> E and not E

The paper you returned to your boss was what he asked for and was not he =
asked for ( =3D "maybe" what he asked for)

So how do Euphoria handle this?

      atom e,=20

      e =3D 2  -- what he asked for
      f =3D 3 -- what you gave him
      if (f =3D e) and not ( f !=3D e) then print( 1, 1)
      else print ( 1, 0)
      end if

      object line
      line =3D gets( 0)


The Euphoria program returns "0" ...... which is wrong!

"not E and E" is unsolvable, neither true nor false.=20
Euphoria cannot handle this (like C and Pascal).

Rom