OpenEuphoria

Re: strong typing and error handling

• Posted by Pete Lomax <petelomax at blueyonder.co.uk> Jun 27, 2003
• 365 views

On Fri, 27 Jun 2003 18:56:33 +1000, Derek Parnell
<ddparnell at bigpond.com> wrote:

WOW, Derek you blew my fuse...
>
>
>On Fri, 27 Jun 2003 07:55:08 +0000 (06/27/03 17:55:08)
>, Peter Willems <peter at integratedmoves.com> wrote:
>
>>
>> Maybe I'm shooting myself in the foot here, but....
>>
>> One of the things in Eu that I really like is the rule-like
>> variable typing that let us set boundaries for a variable.
>> But it seems to me that the absense of an error-handler makes
>> this close to useless because when I try to load a value into
>> a variable that is outside it's boundaries, it exits the app
>> with an error message. Thus I need to have my app check anyway
>> when putting values into vars to prevent my app from exiting,
>> so when I have to check var boundaries myself, what does the
>> option to set boundaries when defining a var does for me ?
>>
>> Or do I mis something and IS it possible to capture boundary
>> overflow (or underflow) in a simple way so I can write a simpe
>> error-handler ?
>>
>
>You can almost do this, so long as you don't mind not having access to =
any=20
>meta-data.
>
> procedure logerr(sequence msg, object data)
>   printf(2, "Type Failure: %s\n", {msg})
>   pretty_print(2, data, {3})
> end procedure
>
> global type Customer(object x)
>
>  if not sequence(x) then
>	logerr("Customer Type must be a sequence.", x)
>      return 1 -- Return to app
>  end if
>
>  if length(x) !=3D 5 then
>	logerr("Customer Type must have 5 fields.", x)
>      return 1 -- Return to app
>  end if
>
>  ...etc...
>
>  return 1
> end type
>
>
>So long as you always return non-zero from a type definition, your=20
>application won't crash with a 'type' error.

Yes, Got that.
>
>If you don't mind it crashing when an assignment is made you do this...
>
> sequence vTypeDefCrash
> vTypeDefCrash =3D {0}
>
> procedure SetTypeDefCrash( object NewVal)
>  if sequence(NewVal) then
>    if length(vTypeDefCrash) > 1 then
>       vTypeDefCrash =3D vTypeDefCrash[2..length(vTypeDefCrash)]
Help!
>       return
>    end if  else
>    vTypeDefCrash =3D NewVal & vTypeDefCrash
Ditto!
>  end if
> end procedure
>
I want to understand here, but I don't

> global type Customer(object x)
>
>  if not sequence(x) then
>	logerr("Customer Type must be a sequence.", x)
>      return vTypeDefCrash[1]
>  end if
>
>  if length(x) !=3D 5 then
>	logerr("Customer Type must have 5 fields.", x)
>      return vTypeDefCrash[1]
>  end if
>
>  ...etc...
>
>  return 1
> end type
> So that by default it would crash except when you don't want it to =
crash=20
>during a certain part of you code...
>
>  SetTypeDefCrash(1) -- Turn on crash avoidance
>  . . . -- critical code
>  SetTypeDefCrash("") -- Restore it to whatever it was.
>
Are you trying to push() and pop() error handling status?

>Unfortunately, you can't tell the user what line of code this was on, or=
=20
>the name of the variable, or even what source file it was in. --
>
>cheers,
>Derek Parnell

Pete