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<p class="MsoNormal">What I would like to see is something like:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span style="font-family:"Courier New"">HsApp (HsApp (HsApp (HsVar "foldl'") (HsVar "+")) (HsLit 0)) (HsVar "xs")</span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Verdana","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Verdana","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Verdana","sans-serif";color:#1F497D">We could derive ‘Show’ on everything but that would generate a LOT of new code, that would seldom be used. Also ‘Show’ doesn’t pretty-print so the result would
be illegible. <o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Verdana","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Verdana","sans-serif";color:#1F497D">I’m a bit dubious. Maybe a better thing might be to improve the existing pretty-printer so it gave you the cues you are looking for?<br>
<br>
S<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Verdana","sans-serif";color:#1F497D"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span lang="EN-US" style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">From:</span></b><span lang="EN-US" style="font-size:10.0pt;font-family:"Tahoma","sans-serif""> ghc-devs-bounces@haskell.org [mailto:ghc-devs-bounces@haskell.org]
<b>On Behalf Of </b>Johan Tibell<br>
<b>Sent:</b> 08 March 2013 07:08<br>
<b>To:</b> ghc-devs@haskell.org<br>
<b>Subject:</b> Show-like output of GHC data types<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I'm trying to better understand how a GHC produced TypedcheckedSource is composed. I have this little example:<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><span style="font-family:"Courier New"">module Test</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Courier New""> ( mysum</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Courier New""> ) where</span><o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><span style="font-family:"Courier New"">import Data.List (foldl')</span><o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><span style="font-family:"Courier New"">mysum :: [Int] -> Int</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Courier New"">mysum xs = foldl' (+) 0 xs</span><o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Pretty-printing TypecheckedSource gives me something like this:<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><span style="font-family:"Courier New"">{{Test.hs:7:10-21}</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Courier New""> AbsBinds [] []</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Courier New""> {Exports: [main:Test.mysum{v rgu} [lid] <= mysum{v agP} [lid]</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Courier New""> <>]</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Courier New""> Exported types: main:Test.mysum{v rgu} [lid]</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Courier New""> :: [ghc-prim:<a href="http://GHC.Types.Int">GHC.Types.Int</a>{(w) tc 3J}]</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Courier New""> -> ghc-prim:<a href="http://GHC.Types.Int">GHC.Types.Int</a>{(w) tc 3J}</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Courier New""> [LclId]</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Courier New""> Binds: {Test.hs:8:1-26}</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Courier New""> mysum{v agP} [lid]</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Courier New""> :: [ghc-prim:<a href="http://GHC.Types.Int">GHC.Types.Int</a>{(w) tc 3J}]</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Courier New""> -> ghc-prim:<a href="http://GHC.Types.Int">GHC.Types.Int</a>{(w) tc 3J}</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Courier New""> [LclId]</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Courier New""> mysum{v agP} [lid]</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Courier New""> ((xs{v agw} [lid] :: [ghc-prim:<a href="http://GHC.Types.Int">GHC.Types.Int</a>{(w) tc 3J}]))</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Courier New""> = {Test.hs:8:12-26}</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Courier New""> (base:Data.List.foldl'{v r4u}) @ ghc-prim:<a href="http://GHC.Types.Int">GHC.Types.Int</a>{(w) tc 3J}</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Courier New""> @ ghc-prim:<a href="http://GHC.Types.Int">GHC.Types.Int</a>{(w) tc 3J}</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Courier New""> (((base:GHC.Num.+{v rt})) @ ghc-prim:<a href="http://GHC.Types.Int">GHC.Types.Int</a>{(w) tc 3J}</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Courier New""> $dNum{v agU} [lid])</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Courier New""> 0 ((base:GHC.Num.fromInteger{v 02A})</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Courier New""> @ ghc-prim:<a href="http://GHC.Types.Int">GHC.Types.Int</a>{(w) tc 3J}</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Courier New""> $dNum{v ahc} [lid]</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Courier New""> 0)</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Courier New""> xs{v agw}</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Courier New""> <></span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Courier New""> Evidence: EvBinds{}}} {Test.hs:7:1-21}</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Courier New""> main:Test.mysum{v rgu} ::</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Courier New""> {Test.hs:7:10-21}</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Courier New""> [ghc-prim:<a href="http://GHC.Types.Int">GHC.Types.Int</a>{(w) tc 3J}]</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Courier New""> -> ghc-prim:<a href="http://GHC.Types.Int">GHC.Types.Int</a>{(w) tc 3J}</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Courier New""> nonrec {Test.hs:8:1-26}</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Courier New""> main:Test.mysum{v rgu}</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Courier New""> main:Test.mysum{v rgu} (xs{v agw})</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Courier New""> = {Test.hs:8:12-26}</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Courier New""> base:Data.List.foldl'{v r4u}</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Courier New""> (base:GHC.Num.+{v rt})</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Courier New""> 0 (base:GHC.Num.fromInteger{v 02A})</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Courier New""> xs{v agw}</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Courier New""> <></span><o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">This doesn't really help me understand the AST any better, as this is essentially the source printed back to me. What I would like to see is something like:<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><span style="font-family:"Courier New"">HsApp (HsApp (HsApp (HsVar "foldl'") (HsVar "+")) (HsLit 0)) (HsVar "xs")</span><o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Is this possible today. If not, can we derive Show for all the GHC data types so it's possible to print their structure?<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">P.S. An example of why the pretty-printed output is not very helpful in understanding the AST: the above simple example generates a HsWrap constructor, which is nowhere to be seen in the pretty-printed output.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">-- Johan<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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