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<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif;mso-fareast-language:EN-US">But what is the inferred type for<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif;mso-fareast-language:EN-US">f x = do { [v] <- x, return v }<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif;mso-fareast-language:EN-US">I think the proposal is to have a MonadFail constraint.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif;mso-fareast-language:EN-US">As far as I understand what you are saying, it would make sense for<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif;mso-fareast-language:EN-US"> f :: Monad m => m [a] -> m a<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif;mso-fareast-language:EN-US"> g x = do { [v] <- x; return v }<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif;mso-fareast-language:EN-US">(with failure giving a runtime error).<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif;mso-fareast-language:EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif">From:</span></b><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif"> Libraries [mailto:libraries-bounces@haskell.org]
<b>On Behalf Of </b>Johan Tibell<br>
<b>Sent:</b> 10 June 2015 14:01<br>
<b>To:</b> Mario Blažević<br>
<b>Cc:</b> Haskell Libraries<br>
<b>Subject:</b> Re: MonadFail proposal (MFP): Moving fail out of Monad<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:6.0pt;margin-right:0cm;margin-bottom:6.0pt;margin-left:0cm">
An idea. Could the new desugaring be the same as for normal functions with a missing case? Code that uses fail would have to add the constraint still, but code that really didn't want to use fail would 1) get a warning about an incomplete pattern match and
2) get a runtime error for the failed pattern match produced by GHC. Is there anything I'm not thinking of here why this wouldn't work?<o:p></o:p></p>
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