<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>
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