Re: CATCH

Thanks for the replies Elizabeth and Rick. After some further study, I
believe this is sinking in.

However, in Rick's example I think there is an extra DROP. If CATCH
returns non-zero, the stack depth would equal the stack depth before the
CATCH plus one for the return code. In other words, the stack depth
will be restored but the stack *content* is indeterminate.

The three items dropped if catch returns true are not predictable.

Thanks,

Mike

----------------------------------------------------

VARIABLE POO

: TEST ( a b -- )
   + POO ! POO @ 100 > THROW ;

: TRY ( a b -- )
   ['] TEST CATCH IF
      ( We now cleanup stack - depth is known, contents is NOT )
      DROP DROP ( DROP ) \ <<< One too Many???
      ." Poo is greater than 100"
   THEN ;

-----Original Message-----
From: sftalk-bounce_at_forth.com [mailto:sftalk-bounce_at_forth.com]On Behalf
Of Rick VanNorman
Sent: Wednesday, April 04, 2001 10:56 AM
To: sftalk_at_forth.com
Subject: [sftalk] Re: CATCH

For instance,

VARIABLE POO

: TEST ( a b -- )
   + POO ! POO @ 100 > THROW ;

: TRY ( a b -- )
   ['] TEST CATCH IF DROP DROP DROP
      ." Poo is greater than 100"
   THEN ;

The three items dropped if catch returns true are not predictable.
If catch returns zero, the stack effect is exactly what the word
caught would be.

Hope this helps.

Rick

*********** REPLY SEPARATOR ***********

On 4/4/2001 at 10:35 AM Mike Ghan wrote:

>Hello all, does each CATCH require a matching THROW or is it possible
>to use CATCH alone and simply drop it's result. For example:
>
>['] FOO CATCH ( throw_code ) \ FOO creates structures
> \ which must be destroyed.
>['] CLEANUP CATCH DROP \ Need to return here
> \ regardless of error.
>DESTROY-FOO \ Destroy FOO's structures.
>( throw-code ) THROW \ Act on first CATCH
> \ throw code.
>

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Received on Wed Apr 04 2001 - 12:49:46 PDT