OpenEuphoria

Re: atom() ambiguity

• Posted by Daniel Berstein <daber at PAIR.COM> Jun 22, 1998
• 669 views

-----Original Message-----
De: Carl R. White <C.R.White at SCM.BRAD.AC.UK>
Para: EUPHORIA at cwisserver1.mcs.muohio.edu
<EUPHORIA at cwisserver1.mcs.muohio.edu>
Fecha: lunes 22 de junio de 1998 12:26
Asunto: Re: atom() ambiguity

>> type boolean (integer x)
>>     if x then            -- If 'x' is != 0
>>         return 1
>>     else
>>         return 0        -- If x = 0
>> end type
>
>This code won't work. A program would crash if it a boolean was set to
>false(0) and wouldn't crash if x = 7 (for instance).

Quite right Carl... Mea Culpa ;)

>After thinking a lot recently, this is the best solution (IMHO):
>
>constant TypeFail = 0
>constant True = 1, False = 0
>
>type boolean(object x)
>    if not integer(x) then
>        return TypeFail
>    end if
>    return x=not(not x)
>end type

Does it work? If x=False (0) then:
    return x=not(not x)
    return x=not(1)
    return x=0 --->False
Isn't this the same I posted before, giving a type_check error?

The type declaration should be:

type boolean(object x)
    integer t
    if sequence(x) then
        if length(x) = 0 then
            t = 0
        else
            for i=1 to length(x)-1 do
                t = boolean(x[i]) and boolean(x[i+1])
            end for
        end if
    else
        t = 1
    end if
    return t
end type

This type declaration says an object is a valid boolean variable if and only
if:
1.- It's an atom (can be true or false).
2.- It's a tautological (all true: != 0)or completly negational (all false:
= 0) sequence.

Regards,
    Daniel  Berstein
    daber at pair.com