OpenEuphoria

Re: atom() ambiguity

• Posted by "Carl R. White" <C.R.White at SCM.BRAD.AC.UK> Jun 23, 1998
• 770 views

On Mon, 22 Jun 1998, Daniel Berstein wrote:


> Carl R. White wrote:
> >> 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?

Errm... (/me thinks hard) It does work.
I'm not returning 0, I'm returning *(x = 0)*...

if x = 0 then (x = not(not 0))
           => (x = not(1))
           => (x = 0)
           => True => 1 => no failure

if x = 1 then (x = not(not 1))
           => (x = not(0))
           => (x = 1)
           => True => 1 => no failure

The function not(not x) will always return 1 or 0, so *any other* values
cause a type_check failure.

> 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

If you wanted a boolean_sequence type then this is it:

type boolseq(object x)
    if not sequence(x)
        return TypeFail -- Defined as 0
    end if
    return compare(x, not(not x)) = 0
end type

Combining the two types is easier and a lot simpler than it seems:

type boolobj(object x)
    return compare({x}, not(not {x})) = 0
end type

This is fun... :)

--
Carl R White
E-mail...: cyrek- at -bigfoot.com              / Remove the hyphens before
Finger...: crwhite- at -dcsun1.comp.brad.ac.uk \ mailing or fingering...
Url......: http://www.bigfoot.com/~cyrek/