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Mariano Martinez Peck

better error handling

Hi folks: First of all I have to say I am pretty sad that error handling hasn't a special place in the PBE. In my opinion having a good error handling is a MUST in every piece of code. We need to use exceptions. I didn't collaborate at all with PBE so I cannot say anything to no one :)   I will try to write something for the next version if you want. But first...

We need a better error handling. It is very common to have a hierarchy of exceptions or errors. You have subclasses of Error for example. And many times, you want to do or not to do or even do something different depending on the error you got. Now, the question is, how you do this in Squeak ???

This is the only (ugly) way I find to do it:

[ a block of code where you do something that can singal different exceptions ]
     on: XXXErrror do: [ : ex | ex class = XXXError if True: [ 'I do what I need to do when I get the error XXX' ].
                                          ex class = YYYError if True: [ 'I do what I need to do when I get the error YYY' ].
                                          'here I do in the rest of the cases'
]

But, I would like to have something like this:

[ a block of code where you do something that can singal different exceptions ]
    on: XXXError
        do: [ : ex | 'I do what I need to do when I get the error XXX' ]
    on: YYYError
        do: [ : ex | 'I do what I need to do when I get the error YYY' ]
    on: Error
        do: [ : ex | 'here I do in the rest of the cases' ]
    ensure: [ 'Here I do what I always need to do, no matter if there is an error or not' ]

What do you think about this? does someone ever did something like this ? perhaps we can put this as part of 1.1

I listen opinions.

Best,

Mariano

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hernan.wilkinson

Re: better error handling

do this...

[[[[ a block of code where you do something that can singal different exceptions ]
    on: XXXError
    do: [ : ex | 'I do what I need to do when I get the error XXX' ]]
    on: YYYError
    do: [ : ex | 'I do what I need to do when I get the error YYY' ]]
    on: Error
    do: [ : ex | 'here I do in the rest of the cases' ]]
    ensure: [ 'Here I do what I always need to do, no matter if there is an error or not' ]

2009/10/1 Mariano Martinez Peck <[hidden email]>

Hi folks: First of all I have to say I am pretty sad that error handling hasn't a special place in the PBE. In my opinion having a good error handling is a MUST in every piece of code. We need to use exceptions. I didn't collaborate at all with PBE so I cannot say anything to no one :)   I will try to write something for the next version if you want. But first...

We need a better error handling. It is very common to have a hierarchy of exceptions or errors. You have subclasses of Error for example. And many times, you want to do or not to do or even do something different depending on the error you got. Now, the question is, how you do this in Squeak ???

This is the only (ugly) way I find to do it:

[ a block of code where you do something that can singal different exceptions ]
     on: XXXErrror do: [ : ex | ex class = XXXError if True: [ 'I do what I need to do when I get the error XXX' ].
                                          ex class = YYYError if True: [ 'I do what I need to do when I get the error YYY' ].
                                          'here I do in the rest of the cases'
]

But, I would like to have something like this:

[ a block of code where you do something that can singal different exceptions ]
    on: XXXError
        do: [ : ex | 'I do what I need to do when I get the error XXX' ]
    on: YYYError
        do: [ : ex | 'I do what I need to do when I get the error YYY' ]
    on: Error
        do: [ : ex | 'here I do in the rest of the cases' ]
    ensure: [ 'Here I do what I always need to do, no matter if there is an error or not' ]

What do you think about this? does someone ever did something like this ? perhaps we can put this as part of 1.1

I listen opinions.

Best,

Mariano

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Stéphane Ducasse

Re: better error handling

In reply to this post by Mariano Martinez Peck

On Oct 1, 2009, at 8:02 PM, Mariano Martinez Peck wrote:

> Hi folks: First of all I have to say I am pretty sad that error
> handling hasn't a special place in the PBE. In my opinion having a
> good error handling is a MUST in every piece of code. We need to use
> exceptions. I didn't collaborate at all with PBE so I cannot say
> anything to no one :) I will try to write something for the next
> version if you want. But first...

there is a chapter for the volume two. It is already written and was
rewritten we will release it in the future for making the unpatient
happy.

> We need a better error handling. It is very common to have a
> hierarchy of exceptions or errors. You have subclasses of Error for
> example. And many times, you want to do or not to do or even do
> something different depending on the error you got. Now, the
> question is, how you do this in Squeak ???

have a look at the Exceptions test because they encode the rich
exception mechanism of Smalltalk.
I could send the exception chapter too :)

>
> This is the only (ugly) way I find to do it:
>
> [ a block of code where you do something that can singal different
> exceptions ]
> on: XXXErrror do: [ : ex | ex class = XXXError if True: [ 'I
> do what I need to do when I get the error XXX' ].
> ex class = YYYError if
> True: [ 'I do what I need to do when I get the error YYY' ].
> 'here I do in the rest of
> the cases'
> ]
>
>
> But, I would like to have something like this:
>
>
> [ a block of code where you do something that can singal different
> exceptions ]
> on: XXXError
> do: [ : ex | 'I do what I need to do when I get the error
> XXX' ]
> on: YYYError
> do: [ : ex | 'I do what I need to do when I get the error
> YYY' ]
> on: Error
> do: [ : ex | 'here I do in the rest of the cases' ]
> ensure: [ 'Here I do what I always need to do, no matter if
> there is an error or not' ]
>
>
> What do you think about this? does someone ever did something like
> this ? perhaps we can put this as part of 1.1
>
> I listen opinions.
>
> Best,
>
> Mariano
> _______________________________________________
> Pharo-project mailing list
> [hidden email]
> http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project

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Mariano Martinez Peck

Re: better error handling

In reply to this post by hernan.wilkinson

2009/10/1 Hernan Wilkinson <[hidden email]>

do this...

[[[[ a block of code where you do something that can singal different exceptions ]
    on: XXXError
    do: [ : ex | 'I do what I need to do when I get the error XXX' ]]
    on: YYYError
    do: [ : ex | 'I do what I need to do when I get the error YYY' ]]
    on: Error
    do: [ : ex | 'here I do in the rest of the cases' ]]
    ensure: [ 'Here I do what I always need to do, no matter if there is an error or not' ]

Thanks Hernán, it is quite better!!! However, I still would love not to use all the brackets ;)
I would use this way for the moment...

2009/10/1 Mariano Martinez Peck <[hidden email]>

Hi folks: First of all I have to say I am pretty sad that error handling hasn't a special place in the PBE. In my opinion having a good error handling is a MUST in every piece of code. We need to use exceptions. I didn't collaborate at all with PBE so I cannot say anything to no one :)   I will try to write something for the next version if you want. But first...

We need a better error handling. It is very common to have a hierarchy of exceptions or errors. You have subclasses of Error for example. And many times, you want to do or not to do or even do something different depending on the error you got. Now, the question is, how you do this in Squeak ???

This is the only (ugly) way I find to do it:

[ a block of code where you do something that can singal different exceptions ]
     on: XXXErrror do: [ : ex | ex class = XXXError if True: [ 'I do what I need to do when I get the error XXX' ].
                                          ex class = YYYError if True: [ 'I do what I need to do when I get the error YYY' ].
                                          'here I do in the rest of the cases'
]

But, I would like to have something like this:

[ a block of code where you do something that can singal different exceptions ]
    on: XXXError
        do: [ : ex | 'I do what I need to do when I get the error XXX' ]
    on: YYYError
        do: [ : ex | 'I do what I need to do when I get the error YYY' ]
    on: Error
        do: [ : ex | 'here I do in the rest of the cases' ]
    ensure: [ 'Here I do what I always need to do, no matter if there is an error or not' ]

What do you think about this? does someone ever did something like this ? perhaps we can put this as part of 1.1

I listen opinions.

Best,

Mariano

_______________________________________________
Pharo-project mailing list
[hidden email]
http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project

_______________________________________________
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[hidden email]
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Mariano Martinez Peck

Re: better error handling

In reply to this post by Stéphane Ducasse

On Thu, Oct 1, 2009 at 3:54 PM, Stéphane Ducasse <[hidden email]> wrote:

On Oct 1, 2009, at 8:02 PM, Mariano Martinez Peck wrote:

> Hi folks: First of all I have to say I am pretty sad that error
> handling hasn't a special place in the PBE. In my opinion having a
> good error handling is a MUST in every piece of code. We need to use
> exceptions. I didn't collaborate at all with PBE so I cannot say
> anything to no one :) I will try to write something for the next
> version if you want. But first...

there is a chapter for the volume two. It is already written and was
rewritten we will release it in the future for making the unpatient
happy.

excellent

> We need a better error handling. It is very common to have a
> hierarchy of exceptions or errors. You have subclasses of Error for
> example. And many times, you want to do or not to do or even do
> something different depending on the error you got. Now, the
> question is, how you do this in Squeak ???

have a look at the Exceptions test because they encode the rich
exception mechanism of Smalltalk.

Ok, I will do that then.

I could send the exception chapter too :)

please do!!!

>
> This is the only (ugly) way I find to do it:
>
> [ a block of code where you do something that can singal different
> exceptions ]
> on: XXXErrror do: [ : ex | ex class = XXXError if True: [ 'I
> do what I need to do when I get the error XXX' ].
> ex class = YYYError if
> True: [ 'I do what I need to do when I get the error YYY' ].
> 'here I do in the rest of
> the cases'
> ]
>
>
> But, I would like to have something like this:
>
>
> [ a block of code where you do something that can singal different
> exceptions ]
> on: XXXError
> do: [ : ex | 'I do what I need to do when I get the error
> XXX' ]
> on: YYYError
> do: [ : ex | 'I do what I need to do when I get the error
> YYY' ]
> on: Error
> do: [ : ex | 'here I do in the rest of the cases' ]
> ensure: [ 'Here I do what I always need to do, no matter if
> there is an error or not' ]
>
>
> What do you think about this? does someone ever did something like
> this ? perhaps we can put this as part of 1.1
>
> I listen opinions.
>
> Best,
>
> Mariano

> _______________________________________________
> Pharo-project mailing list
> [hidden email]
> http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project

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Benjamin Pollack

Re: better error handling

In reply to this post by Mariano Martinez Peck

2009/10/1 Mariano Martinez Peck <[hidden email]>

Thanks Hernán, it is quite better!!! However, I still would love not to use all the brackets ;)
I would use this way for the moment...

As a compromise, you could do what Array does with its with:with:with:with: style thing and make BlockClosure>>on:do:on:do:on:do:, nesting the blocks yourself. Alternatively, it'd be quite easy to add BlockClosure>>onAllDo:, which took a Dictionary mapping exception classes to blocks and called the appropriate one based on the actual exception raised. With the recent closure changes, your blocks will actually work as expected, too, rather than trampling random method variables on execution. :)

--Benjamin

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Igor Stasenko

Re: better error handling

In reply to this post by Mariano Martinez Peck

2009/10/1 Mariano Martinez Peck <[hidden email]>:

>
>
> 2009/10/1 Hernan Wilkinson <[hidden email]>
>>
>> do this...
>>
>> [[[[ a block of code where you do something that can singal different
>> exceptions ]
>>     on: XXXError
>>     do: [ : ex | 'I do what I need to do when I get the error XXX' ]]
>>     on: YYYError
>>     do: [ : ex | 'I do what I need to do when I get the error YYY' ]]
>>     on: Error
>>     do: [ : ex | 'here I do in the rest of the cases' ]]
>>     ensure: [ 'Here I do what I always need to do, no matter if there is
>> an error or not' ]
>>
>

How about a visitor pattern?

[ a block of code where you do something that can singal different exceptions ]
on: Error do: [:ex |
ex visitWith: self
]

and then in each error subclass, you can do

visitWith: handler
^ handler handleXXXerror: self

while, by default, Error could implement this method as:

visitWith: handler
^ handler handleError: self

so, instead of bunch of cases, you having a bunch of methods, which
handling particular case.

--
Best regards,
Igor Stasenko AKA sig.

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Alexandre Bergel

Re: better error handling

In reply to this post by Mariano Martinez Peck

> there is a chapter for the volume two. It is already written and was
> rewritten we will release it in the future for making the unpatient
> happy.
>
> excellent

We put a lot of work in this chapter. Getting the semantic and
explanation right was not trivial.

Alexandre

--
_,.;:~^~:;._,.;:~^~:;._,.;:~^~:;._,.;:~^~:;._,.;:
Alexandre Bergel http://www.bergel.eu
^~:;._,.;:~^~:;._,.;:~^~:;._,.;:~^~:;._,.;:~^~:;.

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Alex Schenkman

Re: better error handling

In reply to this post by Igor Stasenko

Igor,

I'm trying to understand your suggestion.

Am I thinking correclty?

Thanks in advance!

On Thu, Oct 1, 2009 at 23:42, Igor Stasenko <[hidden email]> wrote:

How about a visitor pattern?

[ a block of code where you do something that can singal different exceptions ]

on: Error do: [:ex |
ex visitWith: self
]

I had to replace self with a class handling the errors:

[ZeroDivide new signal: 'zero']

on: Error do:

[:error | error visitWith: (MyErrorHandler new)].

Error>>visitWith: anErrorHandler

^ anErrorHandler handleError: self

MyErrorHandler>>handleError: anError

^anError signal

Error subclass: #AlexError

AlexError>>visitWith: anErrorHandler

^ anErrorHandler handleAlexError: self

AlexError>>handleAlexError: anAlexError

^'Handling an AlexError now.'

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Igor Stasenko

Re: better error handling

2009/10/2 Alex Schenkman <[hidden email]>:

> Igor,
> I'm trying to understand your suggestion.
> Am I thinking correclty?
> Thanks in advance!
> On Thu, Oct 1, 2009 at 23:42, Igor Stasenko <[hidden email]> wrote:
>>
>> How about a visitor pattern?
>>
>> [ a block of code where you do something that can singal different
>> exceptions ]
>> on: Error do: [:ex |
>> ex visitWith: self
>> ]
>>
> I had to replace self with a class handling the errors:
> [ZeroDivide new signal: 'zero']
>    on: Error do:
> [:error | error visitWith: (MyErrorHandler new)].
>
> Error>>visitWith: anErrorHandler
>    ^ anErrorHandler handleError: self
>
> MyErrorHandler>>handleError: anError
>    ^anError signal
>
>
> Error subclass: #AlexError
> AlexError>>visitWith: anErrorHandler
>    ^ anErrorHandler handleAlexError: self
> AlexError>>handleAlexError: anAlexError
>    ^'Handling an AlexError now.'
>
>

yes, something like that
>
> _______________________________________________
> Pharo-project mailing list
> [hidden email]
> http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project
>

--
Best regards,
Igor Stasenko AKA sig.

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