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List: haskell-cafe
Subject: Re: [Haskell-cafe] IO Exceptions through monad transformers stack
From: Nicola Gigante <nicola.gigante () gmail ! com>
Date: 2014-10-08 9:12:42
Message-ID: 94A909C1-745A-4185-AE5A-28C47BF54E77 () gmail ! com
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Il giorno 08/ott/2014, alle ore 00:44, Nikita Volkov <nukasu.kanaka@gmail.com> ha \
scritto:
> Hi Nicola,
>
Hi!
> Exceptions are a completely unrelated mechanism to all the monad transformers. \
> Roughly speaking, it's a dirty low level hack into Haskell's type system. The \
> error-transformer solutions on the other hand are just libraries, which utilize \
> Haskell's standard features. So there is no relation between the two, other then \
> that they approach the same set of problems.
> Concerning your specific problem, the try function is there to help you. In your \
> final solution you may utilize a function in the spirit of the following:
> data ParserError =
> IOError IOException | LexingError <fields> | ParsingError <fields>
>
> safeLiftIO :: IO a -> Parser a
> safeLiftIO io =
> liftIO (try io) >>= either (throwError . IOError) return
Thank you, this solves my problem.
I understand that exceptions are a different mechanism from ExceptT
and similar, but I'm still trying to understand how exceptions are supposed
to be integrated with the other error handling mechanisms (or vice versa).
Any pointers to better understand what components are involved and
best practices for addressing this problems?
> Best regards,
> Nikita Volkov
>
>
Thank you,
Nicola
[Attachment #5 (unknown)]
<html><head><meta http-equiv="Content-Type" content="text/html \
charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; \
-webkit-line-break: after-white-space;"><br><div><div>Il giorno 08/ott/2014, alle ore \
00:44, Nikita Volkov <<a \
href="mailto:nukasu.kanaka@gmail.com">nukasu.kanaka@gmail.com</a>> ha \
scritto:</div><br class="Apple-interchange-newline"><blockquote type="cite"><div \
dir="ltr"><div></div><div class="markdown-here-wrapper" style=""><p \
style="margin:1.2em 0px!important">Hi \
Nicola,</p></div></div></blockquote><div>Hi!</div><blockquote type="cite"><div \
dir="ltr"><div class="markdown-here-wrapper" style=""><p style="margin:1.2em \
0px!important">Exceptions are a completely unrelated mechanism to all the monad \
transformers. Roughly speaking, it's a dirty low level hack into Haskell's type \
system. The error-transformer solutions on the other hand are just libraries, which \
utilize Haskell's standard features. So there is no relation between the two, other \
then that they approach the same set of problems.</p><p style="margin:1.2em \
0px!important">Concerning your specific problem, the <a \
href="http://hackage.haskell.org/package/base-4.7.0.1/docs/Control-Exception-Base.html#v:try"><code \
style="font-size:0.85em;font-family:Consolas,Inconsolata,Courier,monospace;margin:0px \
0.15em;padding:0px 0.3em;white-space:pre-wrap;border:1px solid \
rgb(234,234,234);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom- \
right-radius:3px;border-bottom-left-radius:3px;display:inline;background-color:rgb(248,248,248)">try</code></a> \
function is there to help you. In your final solution you may utilize a function in \
the spirit of the following:</p> <pre \
style="font-size:0.85em;font-family:Consolas,Inconsolata,Courier,monospace;font-size:1em;line-height:1.2em;margin:1.2em \
0px"><code style="font-size:0.85em;font-family:Consolas,Inconsolata,Courier,monospace;margin:0px \
0.15em;padding:0px 0.3em;white-space:pre-wrap;border:1px solid \
rgb(234,234,234);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom- \
right-radius:3px;border-bottom-left-radius:3px;display:inline;background-color:rgb(248 \
,248,248);white-space:pre;overflow:auto;border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px;border:1px \
solid rgb(204,204,204);padding:0.5em \
0.7em;display:block!important;display:block;padding:0.5em;color:rgb(51,51,51);background:rgb(248,248,255)">data \
ParserError = IOError IOException | LexingError <fields> | ParsingError \
<fields>
safeLiftIO :: IO a -> Parser a
safeLiftIO io =
liftIO (try io) >>= either (throwError . IOError) return
</code></pre></div></div></blockquote><div>Thank you, this solves my \
problem.</div><div>I understand that exceptions are a different mechanism from \
ExceptT</div><div>and similar, but I'm still trying to understand how exceptions are \
supposed</div><div>to be integrated with the other error handling mechanisms (or vice \
versa).</div><div><br></div><div>Any pointers to better understand what components \
are involved and</div><div>best practices for addressing this \
problems?</div><blockquote type="cite"><div dir="ltr"><div \
class="markdown-here-wrapper" style=""><p style="margin:1.2em 0px!important">Best \
regards,<br>Nikita Volkov</p> <div \
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style="height:0;font-size:0em;padding:0;margin:0"></div></div><div></div></div></blockquote></div><br><div>Thank \
you,</div><div>Nicola</div></body></html>
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