John M. McIntosh <johnmci at smalltalkconsulting.com> wrote:
>Hi, many years ago I worked with a 4GL that support this, however it was
>true, false, null. Some interesting things happened because.
>
>true & null -> null
>false & null -> null
>false = null -> null
>
>null ifTrue -> nope
>null ifFalse -> yes!
>

In the scheme I'm using, unknown is either true or false, but we don't know
which.  This leads to:

true & unknown -> unknown
false & unknown -> false

true | unknown -> true
false | unknown -> unknown

x ifFalse: [] in this scheme means "if we know that x is false, do the block",
so

unknown ifFalse -> no!

which seems to make a little more sense.  However,

(x not) ifFalse
x ifTrue

now have different behavior...

>This of course doesn't answer your question, but be careful about control
>statements that are binary in logic.

I will

:)
Russell


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Russell Allen

russell.allen at firebirdmedia.com

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