<div dir="ltr"><div class="markdown-here-wrapper" style=""><p style="margin:0px 0px 1.2em!important">Hi all,</p>
<p style="margin:0px 0px 1.2em!important">Could you offer some insight into newtypes at the STG level? Here’s the<br>context:</p>
<ol style="margin:1.2em 0px;padding-left:2em">
<li style="margin:0.5em 0px"><p style="margin:0px 0px 1.2em!important;margin:0.5em 0px!important">I’m working on this interpreter for STG<br>(<a href="https://github.com/chrisdone/prana">https://github.com/chrisdone/prana</a>) and I’m trying to generate a<br>pristine AST where all names in it are resolved to something known to<br>me.</p>
</li>
<li style="margin:0.5em 0px"><p style="margin:0px 0px 1.2em!important;margin:0.5em 0px!important">I’ve compiled ghc-prim and integer-gmp without issue, and I’m<br>compiling base and there remains one last frontier which is newtypes.</p>
</li>
</ol>
<p style="margin:0px 0px 1.2em!important">These are the culprits pointed out if I compile base:</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);background-color:rgb(248,248,248);border-radius:3px;display:inline;white-space:pre;overflow:auto;border-radius:3px;border:1px solid rgb(204,204,204);padding:0.5em 0.7em;display:block!important">chris@precision:~/Work/chrisdone/prana/ghc-8.4/libraries/base-4.11.1.0$ PRANA_INDEX=../prana.idx stack build --exec './Setup build --ghc-options=-O0' --file-watch
Preprocessing library for base-4.11.1.0..
Building library for base-4.11.1.0..
[1 of 244] Compiling GHC.Base
[2 of 244] Compiling <a href="http://GHC.IO">GHC.IO</a>
[3 of 244] Compiling GHC.Real
[4 of 244] Compiling Data.Semigroup.Internal
... [snip] ...
[242 of 244] Compiling Data.Functor.Compose
[243 of 244] Compiling Data.Fixed
[244 of 244] Compiling Data.Complex

Errors in Data.Foldable:
  Variable name not found: base:Data.Semigroup.Internal.All
  Variable name not found: base:Data.Semigroup.Internal.Any

Errors in Foreign.Marshal.Pool:
  Variable name not found: base:Foreign.Marshal.Pool.Pool

Errors in GHC.ExecutionStack.Internal:
  Variable name not found: base:GHC.ExecutionStack.Internal.StackTrace

Errors in Data.Bifoldable:
  Variable name not found: base:Data.Semigroup.Internal.All
  Variable name not found: base:Data.Semigroup.Internal.Any

Errors in System.Timeout:
  Variable name not found: base:System.Timeout.Timeout

Errors in Data.Data:
  Variable name not found: base:Foreign.Ptr.WordPtr
  Variable name not found: base:Foreign.Ptr.IntPtr
  Variable name not found: base:Data.Semigroup.Internal.Any
  Variable name not found: base:Data.Semigroup.Internal.All
</code></pre><p style="margin:0px 0px 1.2em!important">I looked these up, and they all appear to be <em>uses</em> of a<br>newtype.</p>
<p style="margin:0px 0px 1.2em!important">For example, in the Timeout function:</p>
<p style="margin:0px 0px 1.2em!important"><a href="http://hackage.haskell.org/package/base-4.12.0.0/docs/src/System.Timeout.html#timeout">http://hackage.haskell.org/package/base-4.12.0.0/docs/src/System.Timeout.html#timeout</a></p>
<p style="margin:0px 0px 1.2em!important">I printed out the full [StgTopBinding] list and got:</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 class="hljs language-haskell" 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);background-color:rgb(248,248,248);border-radius:3px;display:inline;white-space:pre;overflow:auto;border-radius:3px;border:1px solid rgb(204,204,204);padding:0.5em 0.7em;display:block!important;display:block;overflow-x:auto;padding:0.5em;color:rgb(51,51,51);background:rgb(248,248,248)"><span class="hljs-title" style="color:rgb(153,0,0);font-weight:bold">let</span> {
  sat_s27NC [<span class="hljs-type" style="color:rgb(68,85,136);font-weight:bold">Occ</span>=<span class="hljs-type" style="color:rgb(68,85,136);font-weight:bold">Once</span>] :: <span class="hljs-type" style="color:rgb(68,85,136);font-weight:bold">IO</span> <span class="hljs-type" style="color:rgb(68,85,136);font-weight:bold">Timeout</span>
  [<span class="hljs-type" style="color:rgb(68,85,136);font-weight:bold">LclId</span>] =
      [] \u [] fmap $fFunctorIO <span class="hljs-type" style="color:rgb(68,85,136);font-weight:bold">Timeout</span> newUnique;
} <span class="hljs-keyword" style="color:rgb(51,51,51);font-weight:bold">in</span>  >>= $fMonadIO sat_s27NC sat_s27NT;
</code></pre>
<p style="margin:0px 0px 1.2em!important">Oddly (or not?), they’re used as values, not constructors. This error<br>comes from this part of my code:</p>
<pre style="font-size:0.85em;font-family:Consolas,Inconsolata,Courier,monospace;font-size:1em;line-height:1.2em;margin:1.2em 0px"><code style="font-size:0.85em;font-family:Consolas,Inconsolata,Courier,monospace;margin:0px 0.15em;padding:0px 0.3em;white-space:pre-wrap;border:1px solid rgb(234,234,234);background-color:rgb(248,248,248);border-radius:3px;display:inline;white-space:pre;overflow:auto;border-radius:3px;border:1px solid rgb(204,204,204);padding:0.5em 0.7em;display:block!important">StgSyn.StgApp occ arguments ->
  AppExpr <$> lookupSomeVarId occ <*> traverse fromStgGenArg arguments
</code></pre><p style="margin:0px 0px 1.2em!important">If it was used as a constructor, it’d appear in this position, where<br>looking up the ID would produce a “Data constructor name not found”<br>error:</p>
<p style="margin:0px 0px 1.2em!important">StgSyn.StgConApp dataCon arguments types -><br>  ConAppExpr <$> lookupDataConId dataCon <<em>> traverse fromStgGenArg arguments <</em>><br>  pure (map (const Type) types)</p>
<p style="margin:0px 0px 1.2em!important">My understanding of newtypes at this stage is hazy. It seems like:</p>
<ul style="margin:1.2em 0px;padding-left:2em">
<li style="margin:0.5em 0px"><p style="margin:0px 0px 1.2em!important;margin:0.5em 0px!important">They ought to be erased and replaced with coercions by now.  If<br>they’re not replaced, it’s because they’re in a not-quite-id position<br>like <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);background-color:rgb(248,248,248);border-radius:3px;display:inline">fmap Timeout ...</code>. (Arguably these could be fixed in base with a<br>Data.Coerce.coerce?)</p>
</li>
<li style="margin:0.5em 0px"><p style="margin:0px 0px 1.2em!important;margin:0.5em 0px!important">However, the CoreTidy/PrepPgm processing modules<br>don’t seem to have removed or replaced these, or introduced a binding<br>that would do something.</p>
</li>
</ul>
<p style="margin:0px 0px 1.2em!important">At this stage what would you recommend? At this point type-checking is<br>done, and I only care about interpreting the code. So I suppose they<br>could be <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);background-color:rgb(248,248,248);border-radius:3px;display:inline">id</code> for all it matters to the interpreter?</p>
<p style="margin:0px 0px 1.2em!important">I imagine they aren’t actually supposed to allocate something here. And<br>I’m certain that any pattern matching on a newtype is also erased away<br>by this point.</p><p style="margin:0px 0px 1.2em!important">Cheers!</p><p style="margin:0px 0px 1.2em!important">Chris</p>
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