<html><head><meta http-equiv="Content-Type" content="text/html charset=windows-1252"><base href="x-msg://979/"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><div>If Lennart's suggestion is combined with GHC's lazy checking for name clashes (i.e., only check if you ever look a name up in a particular scope), it would also work in your example.</div><div><br></div><div>Manuel</div><br><div><div>"Sittampalam, Ganesh" <<a href="mailto:ganesh.sittampalam@credit-suisse.com">ganesh.sittampalam@credit-suisse.com</a>>:</div><blockquote type="cite"><div lang="EN-GB" link="blue" vlink="purple" style="font-family: Helvetica; font-size: medium; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: -webkit-auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; "><div class="WordSection1" style="page: WordSection1; "><div style="margin: 0cm 0cm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif; "><span style="font-size: 10pt; font-family: Arial, sans-serif; ">If you’re using unqualified and unrestricted imports, there’s still the risk that another module will export something you care about, e.g.<o:p></o:p></span></div><div style="margin: 0cm 0cm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif; "><span style="font-size: 10pt; font-family: Arial, sans-serif; "> </span></div><div style="margin: 0cm 0cm 0.0001pt 36pt; font-size: 12pt; font-family: 'Times New Roman', serif; "><span style="font-size: 10pt; font-family: 'Courier New'; ">module M where<o:p></o:p></span></div><div style="margin: 0cm 0cm 0.0001pt 36pt; font-size: 12pt; font-family: 'Times New Roman', serif; "><span style="font-size: 10pt; font-family: 'Courier New'; ">import I -- currently exports foo<o:p></o:p></span></div><div style="margin: 0cm 0cm 0.0001pt 36pt; font-size: 12pt; font-family: 'Times New Roman', serif; "><span style="font-size: 10pt; font-family: 'Courier New'; ">import J -- might be changed in future to export foo<o:p></o:p></span></div><div style="margin: 0cm 0cm 0.0001pt 36pt; font-size: 12pt; font-family: 'Times New Roman', serif; "><span style="font-size: 10pt; font-family: 'Courier New'; "> </span></div><div style="margin: 0cm 0cm 0.0001pt 36pt; font-size: 12pt; font-family: 'Times New Roman', serif; "><span style="font-size: 10pt; font-family: 'Courier New'; ">… foo …<o:p></o:p></span></div><div style="margin: 0cm 0cm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif; "><span style="font-size: 10pt; font-family: Arial, sans-serif; "> </span></div><div style="margin: 0cm 0cm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif; "><span style="font-size: 10pt; font-family: Arial, sans-serif; ">So I think you need to use import lists or qualified anyway to avoid any risk of future name clashes – given that, does this change buy much?<o:p></o:p></span></div><div style="margin: 0cm 0cm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif; "><span style="font-size: 10pt; font-family: Arial, sans-serif; "><o:p></o:p></span></div><div style="margin: 0cm 0cm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif; "><span style="font-size: 10pt; font-family: Arial, sans-serif; color: rgb(192, 80, 77); "> </span></div><div style="margin: 0cm 0cm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif; "><b><span lang="EN-US" style="font-size: 10pt; font-family: Tahoma, sans-serif; ">From:</span></b><span lang="EN-US" style="font-size: 10pt; font-family: Tahoma, sans-serif; "><span class="Apple-converted-space"> </span><a href="mailto:haskell-prime-bounces@haskell.org" style="color: purple; text-decoration: underline; ">haskell-prime-bounces@haskell.org</a><span class="Apple-converted-space"> </span>[mailto:haskell-<a href="mailto:prime-bounces@haskell.org" style="color: purple; text-decoration: underline; ">prime-bounces@haskell.org</a>]<span class="Apple-converted-space"> </span><b>On Behalf Of<span class="Apple-converted-space"> </span></b>Lennart Augustsson<br><b>Sent:</b><span class="Apple-converted-space"> </span>24 July 2012 02:29<br><b>To:</b><span class="Apple-converted-space"> </span>Haskell Prime<br><b>Subject:</b><span class="Apple-converted-space"> </span>Proposal: Scoping rule change<o:p></o:p></span></div><div style="margin: 0cm 0cm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif; "><o:p> </o:p></div><div><div style="margin: 0cm 0cm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif; ">It's not often that one gets the chance to change something as<o:p></o:p></div></div><div><div style="margin: 0cm 0cm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif; ">fundamental as the scoping rules of a language. Nevertheless, I would<o:p></o:p></div></div><div><div style="margin: 0cm 0cm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif; ">like to propose a change to Haskell's scoping rules.<o:p></o:p></div></div><div><div style="margin: 0cm 0cm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif; "><o:p> </o:p></div></div><div><div style="margin: 0cm 0cm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif; ">The change is quite simple. As it is, top level entities in a module<o:p></o:p></div></div><div><div style="margin: 0cm 0cm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif; ">are in the same scope as all imported entities. I suggest that this<o:p></o:p></div></div><div><div style="margin: 0cm 0cm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif; ">is changed to that the entities from the module are in an inner scope<o:p></o:p></div></div><div><div style="margin: 0cm 0cm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif; ">and do not clash with imported identifiers.<o:p></o:p></div></div><div><div style="margin: 0cm 0cm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif; "><o:p> </o:p></div></div><div><div style="margin: 0cm 0cm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif; ">Why? Consider the following snippet<o:p></o:p></div></div><div><div style="margin: 0cm 0cm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif; "><o:p> </o:p></div></div><div><div style="margin: 0cm 0cm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif; "> module M where<o:p></o:p></div></div><div><div style="margin: 0cm 0cm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif; "> import I<o:p></o:p></div></div><div><div style="margin: 0cm 0cm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif; "> foo = True<o:p></o:p></div></div><div><div style="margin: 0cm 0cm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif; "><o:p> </o:p></div></div><div><div style="margin: 0cm 0cm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif; ">Assume this compiles. Now change the module I so it exports something<o:p></o:p></div></div><div><div style="margin: 0cm 0cm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif; ">called foo. After this change the module M no longer compiles since<o:p></o:p></div></div><div><div style="margin: 0cm 0cm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif; ">(under the current scoping rules) the imported foo clashes with the<o:p></o:p></div></div><div><div style="margin: 0cm 0cm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif; ">foo in M.<o:p></o:p></div></div><div><div style="margin: 0cm 0cm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif; "><o:p> </o:p></div></div><div><div style="margin: 0cm 0cm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif; ">Pros: Module compilation becomes more robust under library changes.<o:p></o:p></div></div><div><div style="margin: 0cm 0cm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif; ">Fewer imports with hiding are necessary.<o:p></o:p></div></div><div><div style="margin: 0cm 0cm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif; "><o:p> </o:p></div></div><div><div style="margin: 0cm 0cm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif; ">Cons: There's the chance that you happen to define a module identifier<o:p></o:p></div></div><div><div style="margin: 0cm 0cm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif; ">with the same name as something imported. This will typically lead to<o:p></o:p></div></div><div><div style="margin: 0cm 0cm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif; ">a type error, but there is a remote chance it could have the same<o:p></o:p></div></div><div><div style="margin: 0cm 0cm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif; ">type.<o:p></o:p></div></div><div><div style="margin: 0cm 0cm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif; "><o:p> </o:p></div></div><div><div style="margin: 0cm 0cm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif; ">Implementation status: The Mu compiler has used the scoping rule for<o:p></o:p></div></div><div><div style="margin: 0cm 0cm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif; ">several years now and it works very well in practice.<o:p></o:p></div></div><div><div style="margin: 0cm 0cm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif; "><o:p> </o:p></div></div><div><div style="margin: 0cm 0cm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif; "> -- Lennart<o:p></o:p></div></div><div><div style="margin: 0cm 0cm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif; "><o:p> </o:p></div></div></div><br><div style="margin: 0cm 0cm 0.0001pt; font-size: 12pt; font-family: 'Times New Roman', serif; "><span lang="EN-US" style="font-size: 8pt; font-family: Courier; ">==============================================================================<br>Please access the attached hyperlink for an important electronic communications disclaimer:<br><a href="http://www.credit-suisse.com/legal/en/disclaimer_email_ib.html" style="color: purple; text-decoration: underline; ">http://www.credit-suisse.com/legal/en/disclaimer_email_ib.html</a><br>==============================================================================<o:p></o:p></span></div><br>_______________________________________________<br>Haskell-prime mailing list<br><a href="mailto:Haskell-prime@haskell.org" style="color: purple; text-decoration: underline; ">Haskell-prime@haskell.org</a><br><a href="http://www.haskell.org/mailman/listinfo/haskell-prime" style="color: purple; text-decoration: underline; ">http://www.haskell.org/mailman/listinfo/haskell-prime</a></div></blockquote></div><br></body></html>