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Richard Eisenberg pushed to branch wip/t22519 at <a href="https://gitlab.haskell.org/ghc/ghc" style="color: #1068bf;">Glasgow Haskell Compiler / GHC</a>
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Commits:
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<strong style="font-weight: bold;"><a href="https://gitlab.haskell.org/ghc/ghc/-/commit/efe7c324435dfabf1ec64088fc9d10e0f1c0a0db" style="color: #1068bf;">efe7c324</a></strong>
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<span> by Richard Eisenberg </span> <i> at 2023-01-02T14:02:25-05:00 </i>
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<pre class="commit-message" style='white-space: pre-wrap; display: block; font-size: 0.8125rem; color: #303030; position: relative; font-family: "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; word-break: break-all; word-wrap: break-word; background-color: #fafafa; border-radius: 2px; margin: 0; padding: 8px 12px; border: 1px solid #dbdbdb;'>Add stuff to Note
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2 changed files:
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compiler/GHC/Tc/Solver/Canonical.hs
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compiler/GHC/Tc/Solver/Rewrite.hs
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Changes:
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<a href="https://gitlab.haskell.org/ghc/ghc/-/commit/efe7c324435dfabf1ec64088fc9d10e0f1c0a0db#f018e77421f495c6f75733fee4a511cfe57bebe8" style="color: #1068bf;"><strong style="font-weight: bold;">compiler/GHC/Tc/Solver/Canonical.hs</strong></a>
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<td class="line_content match" style="color: rgba(0,0,0,0.3); padding: inherit;" bgcolor="#fafafa">@@ -1368,8 +1368,39 @@ which in turn gives us</td>
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1368
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<td class="new_line diff-line-num" data-linenumber="1368" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #f0f0f0; border-right-style: solid; padding: inherit;" align="right" bgcolor="#fafafa">
1368
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<td class="line_content" style="padding: inherit;"><pre style='display: block; font-size: 0.8125rem; color: #303030; position: relative; font-family: "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dbdbdb;'> <span id="LC1368" class="line" lang="haskell"><span class="cm" style="color: #998; font-style: italic;"> [W] a ~R# b</span></span>
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<td class="old_line diff-line-num" data-linenumber="1369" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #f0f0f0; border-right-style: solid; padding: inherit;" align="right" bgcolor="#fafafa">
1369
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<td class="new_line diff-line-num" data-linenumber="1369" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #f0f0f0; border-right-style: solid; padding: inherit;" align="right" bgcolor="#fafafa">
1369
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<td class="line_content" style="padding: inherit;"><pre style='display: block; font-size: 0.8125rem; color: #303030; position: relative; font-family: "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dbdbdb;'> <span id="LC1369" class="line" lang="haskell"><span class="cm" style="color: #998; font-style: italic;">which is easier to satisfy.</span></span>
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1370
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<td class="new_line diff-line-num" data-linenumber="1370" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #f0f0f0; border-right-style: solid; padding: inherit;" align="right" bgcolor="#fafafa">
1370
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<td class="line_content" style="padding: inherit;"><pre style='display: block; font-size: 0.8125rem; color: #303030; position: relative; font-family: "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dbdbdb;'> <span id="LC1370" class="line" lang="haskell"></span>
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<td class="old_line diff-line-num old" data-linenumber="1371" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #fac5cd; border-right-style: solid; padding: inherit;" align="right" bgcolor="#f9d7dc">
1371
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<td class="new_line diff-line-num old" data-linenumber="1371" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #fac5cd; border-right-style: solid; padding: inherit;" align="right" bgcolor="#f9d7dc">
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<td class="line_content old" style="padding: inherit;" bgcolor="#fbe9eb"><pre style='display: block; font-size: 0.8125rem; color: #303030; position: relative; font-family: "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dbdbdb;'>-<span id="LC1371" class="line" lang="haskell"><span class="cm" style="color: #998; font-style: italic;">Bottom line: unwrap newtypes before decomposing them!</span></span>
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<td class="old_line diff-line-num old" data-linenumber="1372" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #fac5cd; border-right-style: solid; padding: inherit;" align="right" bgcolor="#f9d7dc">
1372
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<td class="new_line diff-line-num old" data-linenumber="1371" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #fac5cd; border-right-style: solid; padding: inherit;" align="right" bgcolor="#f9d7dc">
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<td class="line_content old" style="padding: inherit;" bgcolor="#fbe9eb"><pre style='display: block; font-size: 0.8125rem; color: #303030; position: relative; font-family: "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dbdbdb;'>-<span id="LC1372" class="line" lang="haskell"><span class="cm" style="color: #998; font-style: italic;">c.f. #9123 comment:52,53 for a compelling example.</span></span>
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<td class="new_line diff-line-num new" data-linenumber="1371" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #c7f0d2; border-right-style: solid; padding: inherit;" align="right" bgcolor="#ddfbe6">
1371
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<td class="line_content new" style="padding: inherit;" bgcolor="#ecfdf0"><pre style='display: block; font-size: 0.8125rem; color: #303030; position: relative; font-family: "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dbdbdb;'>+<span id="LC1371" class="line" lang="haskell"><span class="cm" style="color: #998; font-style: italic;">We thus must unwrap newtypes before decomposing them. But even this is</span></span>
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<td class="new_line diff-line-num new" data-linenumber="1372" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #c7f0d2; border-right-style: solid; padding: inherit;" align="right" bgcolor="#ddfbe6">
1372
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<td class="line_content new" style="padding: inherit;" bgcolor="#ecfdf0"><pre style='display: block; font-size: 0.8125rem; color: #303030; position: relative; font-family: "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dbdbdb;'>+<span id="LC1372" class="line" lang="haskell"><span class="cm" style="color: #998; font-style: italic;">challenging. Here are two cases to consider:</span></span>
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<td class="new_line diff-line-num new" data-linenumber="1373" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #c7f0d2; border-right-style: solid; padding: inherit;" align="right" bgcolor="#ddfbe6">
1373
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<td class="line_content new" style="padding: inherit;" bgcolor="#ecfdf0"><pre style='display: block; font-size: 0.8125rem; color: #303030; position: relative; font-family: "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dbdbdb;'>+<span id="LC1373" class="line" lang="haskell"></span>
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<td class="new_line diff-line-num new" data-linenumber="1374" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #c7f0d2; border-right-style: solid; padding: inherit;" align="right" bgcolor="#ddfbe6">
1374
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<td class="line_content new" style="padding: inherit;" bgcolor="#ecfdf0"><pre style='display: block; font-size: 0.8125rem; color: #303030; position: relative; font-family: "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dbdbdb;'>+<span id="LC1374" class="line" lang="haskell"><span class="cm" style="color: #998; font-style: italic;">Case 1:</span></span>
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<td class="new_line diff-line-num new" data-linenumber="1375" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #c7f0d2; border-right-style: solid; padding: inherit;" align="right" bgcolor="#ddfbe6">
1375
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<td class="line_content new" style="padding: inherit;" bgcolor="#ecfdf0"><pre style='display: block; font-size: 0.8125rem; color: #303030; position: relative; font-family: "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dbdbdb;'>+<span id="LC1375" class="line" lang="haskell"></span>
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<td class="new_line diff-line-num new" data-linenumber="1376" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #c7f0d2; border-right-style: solid; padding: inherit;" align="right" bgcolor="#ddfbe6">
1376
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<td class="line_content new" style="padding: inherit;" bgcolor="#ecfdf0"><pre style='display: block; font-size: 0.8125rem; color: #303030; position: relative; font-family: "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dbdbdb;'>+<span id="LC1376" class="line" lang="haskell"><span class="cm" style="color: #998; font-style: italic;"> newtype Age = MkAge Int</span></span>
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<td class="new_line diff-line-num new" data-linenumber="1377" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #c7f0d2; border-right-style: solid; padding: inherit;" align="right" bgcolor="#ddfbe6">
1377
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<td class="line_content new" style="padding: inherit;" bgcolor="#ecfdf0"><pre style='display: block; font-size: 0.8125rem; color: #303030; position: relative; font-family: "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dbdbdb;'>+<span id="LC1377" class="line" lang="haskell"><span class="cm" style="color: #998; font-style: italic;"> [G] c</span></span>
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<td class="new_line diff-line-num new" data-linenumber="1378" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #c7f0d2; border-right-style: solid; padding: inherit;" align="right" bgcolor="#ddfbe6">
1378
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<td class="line_content new" style="padding: inherit;" bgcolor="#ecfdf0"><pre style='display: block; font-size: 0.8125rem; color: #303030; position: relative; font-family: "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dbdbdb;'>+<span id="LC1378" class="line" lang="haskell"><span class="cm" style="color: #998; font-style: italic;"> [W] w1 :: IO Age ~R# IO Int</span></span>
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<td class="new_line diff-line-num new" data-linenumber="1379" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #c7f0d2; border-right-style: solid; padding: inherit;" align="right" bgcolor="#ddfbe6">
1379
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<td class="line_content new" style="padding: inherit;" bgcolor="#ecfdf0"><pre style='display: block; font-size: 0.8125rem; color: #303030; position: relative; font-family: "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dbdbdb;'>+<span id="LC1379" class="line" lang="haskell"></span>
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<td class="new_line diff-line-num new" data-linenumber="1380" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #c7f0d2; border-right-style: solid; padding: inherit;" align="right" bgcolor="#ddfbe6">
1380
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<td class="line_content new" style="padding: inherit;" bgcolor="#ecfdf0"><pre style='display: block; font-size: 0.8125rem; color: #303030; position: relative; font-family: "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dbdbdb;'>+<span id="LC1380" class="line" lang="haskell"><span class="cm" style="color: #998; font-style: italic;">Case 2:</span></span>
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1381
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<td class="new_line diff-line-num new" data-linenumber="1382" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #c7f0d2; border-right-style: solid; padding: inherit;" align="right" bgcolor="#ddfbe6">
1382
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<td class="line_content new" style="padding: inherit;" bgcolor="#ecfdf0"><pre style='display: block; font-size: 0.8125rem; color: #303030; position: relative; font-family: "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dbdbdb;'>+<span id="LC1382" class="line" lang="haskell"><span class="cm" style="color: #998; font-style: italic;"> newtype A = MkA [A]</span></span>
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<td class="new_line diff-line-num new" data-linenumber="1383" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #c7f0d2; border-right-style: solid; padding: inherit;" align="right" bgcolor="#ddfbe6">
1383
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<td class="line_content new" style="padding: inherit;" bgcolor="#ecfdf0"><pre style='display: block; font-size: 0.8125rem; color: #303030; position: relative; font-family: "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dbdbdb;'>+<span id="LC1383" class="line" lang="haskell"><span class="cm" style="color: #998; font-style: italic;"> [W] A ~R# [A]</span></span>
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<td class="new_line diff-line-num new" data-linenumber="1384" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #c7f0d2; border-right-style: solid; padding: inherit;" align="right" bgcolor="#ddfbe6">
1384
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<td class="line_content new" style="padding: inherit;" bgcolor="#ecfdf0"><pre style='display: block; font-size: 0.8125rem; color: #303030; position: relative; font-family: "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dbdbdb;'>+<span id="LC1384" class="line" lang="haskell"></span>
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<td class="new_line diff-line-num new" data-linenumber="1385" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #c7f0d2; border-right-style: solid; padding: inherit;" align="right" bgcolor="#ddfbe6">
1385
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<td class="line_content new" style="padding: inherit;" bgcolor="#ecfdf0"><pre style='display: block; font-size: 0.8125rem; color: #303030; position: relative; font-family: "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dbdbdb;'>+<span id="LC1385" class="line" lang="haskell"><span class="cm" style="color: #998; font-style: italic;">For Case 1, recall that IO is an abstract newtype. Then read</span></span>
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<td class="new_line diff-line-num new" data-linenumber="1386" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #c7f0d2; border-right-style: solid; padding: inherit;" align="right" bgcolor="#ddfbe6">
1386
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<td class="line_content new" style="padding: inherit;" bgcolor="#ecfdf0"><pre style='display: block; font-size: 0.8125rem; color: #303030; position: relative; font-family: "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dbdbdb;'>+<span id="LC1386" class="line" lang="haskell"><span class="cm" style="color: #998; font-style: italic;">Note [Decomposing newtype equalities]. According to that Note,</span></span>
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<td class="new_line diff-line-num new" data-linenumber="1387" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #c7f0d2; border-right-style: solid; padding: inherit;" align="right" bgcolor="#ddfbe6">
1387
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<td class="line_content new" style="padding: inherit;" bgcolor="#ecfdf0"><pre style='display: block; font-size: 0.8125rem; color: #303030; position: relative; font-family: "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dbdbdb;'>+<span id="LC1387" class="line" lang="haskell"><span class="cm" style="color: #998; font-style: italic;">we should not decompose w1, as we have an Irred Given. Yet we still</span></span>
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<td class="new_line diff-line-num new" data-linenumber="1388" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #c7f0d2; border-right-style: solid; padding: inherit;" align="right" bgcolor="#ddfbe6">
1388
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<td class="line_content new" style="padding: inherit;" bgcolor="#ecfdf0"><pre style='display: block; font-size: 0.8125rem; color: #303030; position: relative; font-family: "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dbdbdb;'>+<span id="LC1388" class="line" lang="haskell"><span class="cm" style="color: #998; font-style: italic;">want to solve the wanted! So we unwrap the newtypes we can, deeply.</span></span>
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<td class="new_line diff-line-num new" data-linenumber="1389" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #c7f0d2; border-right-style: solid; padding: inherit;" align="right" bgcolor="#ddfbe6">
1389
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<td class="line_content new" style="padding: inherit;" bgcolor="#ecfdf0"><pre style='display: block; font-size: 0.8125rem; color: #303030; position: relative; font-family: "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dbdbdb;'>+<span id="LC1389" class="line" lang="haskell"><span class="cm" style="color: #998; font-style: italic;">This is done in the rewriter: GHC.Tc.Solver.Rewrite.rewrite_newtype_app.</span></span>
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<td class="new_line diff-line-num new" data-linenumber="1390" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #c7f0d2; border-right-style: solid; padding: inherit;" align="right" bgcolor="#ddfbe6">
1390
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<td class="line_content new" style="padding: inherit;" bgcolor="#ecfdf0"><pre style='display: block; font-size: 0.8125rem; color: #303030; position: relative; font-family: "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dbdbdb;'>+<span id="LC1390" class="line" lang="haskell"></span>
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<td class="new_line diff-line-num new" data-linenumber="1391" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #c7f0d2; border-right-style: solid; padding: inherit;" align="right" bgcolor="#ddfbe6">
1391
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<td class="line_content new" style="padding: inherit;" bgcolor="#ecfdf0"><pre style='display: block; font-size: 0.8125rem; color: #303030; position: relative; font-family: "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dbdbdb;'>+<span id="LC1391" class="line" lang="haskell"><span class="cm" style="color: #998; font-style: italic;">Yet for Case 2, deep rewriting would be a disaster: we would loop. Instead,</span></span>
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<td class="new_line diff-line-num new" data-linenumber="1392" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #c7f0d2; border-right-style: solid; padding: inherit;" align="right" bgcolor="#ddfbe6">
1392
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<td class="line_content new" style="padding: inherit;" bgcolor="#ecfdf0"><pre style='display: block; font-size: 0.8125rem; color: #303030; position: relative; font-family: "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dbdbdb;'>+<span id="LC1392" class="line" lang="haskell"><span class="cm" style="color: #998; font-style: italic;">here, we just want to unwrap newtypes at the top level, allowing us to</span></span>
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<td class="new_line diff-line-num new" data-linenumber="1393" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #c7f0d2; border-right-style: solid; padding: inherit;" align="right" bgcolor="#ddfbe6">
1393
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<td class="line_content new" style="padding: inherit;" bgcolor="#ecfdf0"><pre style='display: block; font-size: 0.8125rem; color: #303030; position: relative; font-family: "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dbdbdb;'>+<span id="LC1393" class="line" lang="haskell"><span class="cm" style="color: #998; font-style: italic;">succeed via Note [Eager reflexivity check].</span></span>
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<td class="new_line diff-line-num new" data-linenumber="1394" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #c7f0d2; border-right-style: solid; padding: inherit;" align="right" bgcolor="#ddfbe6">
1394
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<td class="line_content new" style="padding: inherit;" bgcolor="#ecfdf0"><pre style='display: block; font-size: 0.8125rem; color: #303030; position: relative; font-family: "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dbdbdb;'>+<span id="LC1394" class="line" lang="haskell"></span>
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<td class="new_line diff-line-num new" data-linenumber="1395" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #c7f0d2; border-right-style: solid; padding: inherit;" align="right" bgcolor="#ddfbe6">
1395
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<td class="line_content new" style="padding: inherit;" bgcolor="#ecfdf0"><pre style='display: block; font-size: 0.8125rem; color: #303030; position: relative; font-family: "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dbdbdb;'>+<span id="LC1395" class="line" lang="haskell"><span class="cm" style="color: #998; font-style: italic;">To satisfy both cases, we unwrap *both* in can_eq_nc' and in the rewriter.</span></span>
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<td class="new_line diff-line-num new" data-linenumber="1396" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #c7f0d2; border-right-style: solid; padding: inherit;" align="right" bgcolor="#ddfbe6">
1396
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<td class="line_content new" style="padding: inherit;" bgcolor="#ecfdf0"><pre style='display: block; font-size: 0.8125rem; color: #303030; position: relative; font-family: "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dbdbdb;'>+<span id="LC1396" class="line" lang="haskell"><span class="cm" style="color: #998; font-style: italic;">The former unwraps outer newtypes (when the data constructor is in scope).</span></span>
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<td class="new_line diff-line-num new" data-linenumber="1397" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #c7f0d2; border-right-style: solid; padding: inherit;" align="right" bgcolor="#ddfbe6">
1397
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<td class="line_content new" style="padding: inherit;" bgcolor="#ecfdf0"><pre style='display: block; font-size: 0.8125rem; color: #303030; position: relative; font-family: "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dbdbdb;'>+<span id="LC1397" class="line" lang="haskell"><span class="cm" style="color: #998; font-style: italic;">The latter unwraps deeply -- but it won't be invoked in Case 2, when we</span></span>
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<td class="new_line diff-line-num new" data-linenumber="1398" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #c7f0d2; border-right-style: solid; padding: inherit;" align="right" bgcolor="#ddfbe6">
1398
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<td class="line_content new" style="padding: inherit;" bgcolor="#ecfdf0"><pre style='display: block; font-size: 0.8125rem; color: #303030; position: relative; font-family: "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dbdbdb;'>+<span id="LC1398" class="line" lang="haskell"><span class="cm" style="color: #998; font-style: italic;">can recognize an equality between the types [A] and [A] before rewriting</span></span>
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<td class="new_line diff-line-num new" data-linenumber="1399" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #c7f0d2; border-right-style: solid; padding: inherit;" align="right" bgcolor="#ddfbe6">
1399
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<td class="line_content new" style="padding: inherit;" bgcolor="#ecfdf0"><pre style='display: block; font-size: 0.8125rem; color: #303030; position: relative; font-family: "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dbdbdb;'>+<span id="LC1399" class="line" lang="haskell"><span class="cm" style="color: #998; font-style: italic;">deeply.</span></span>
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1400
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<td class="line_content new" style="padding: inherit;" bgcolor="#ecfdf0"><pre style='display: block; font-size: 0.8125rem; color: #303030; position: relative; font-family: "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dbdbdb;'>+<span id="LC1400" class="line" lang="haskell"></span>
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<td class="new_line diff-line-num new" data-linenumber="1401" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #c7f0d2; border-right-style: solid; padding: inherit;" align="right" bgcolor="#ddfbe6">
1401
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<td class="line_content new" style="padding: inherit;" bgcolor="#ecfdf0"><pre style='display: block; font-size: 0.8125rem; color: #303030; position: relative; font-family: "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dbdbdb;'>+<span id="LC1401" class="line" lang="haskell"><span class="cm" style="color: #998; font-style: italic;">This is delicate, but I think we're doomed to do *something* delicate,</span></span>
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<td class="old_line diff-line-num new" data-linenumber="1373" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #c7f0d2; border-right-style: solid; padding: inherit;" align="right" bgcolor="#ddfbe6">
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<td class="new_line diff-line-num new" data-linenumber="1402" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #c7f0d2; border-right-style: solid; padding: inherit;" align="right" bgcolor="#ddfbe6">
1402
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<td class="line_content new" style="padding: inherit;" bgcolor="#ecfdf0"><pre style='display: block; font-size: 0.8125rem; color: #303030; position: relative; font-family: "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dbdbdb;'>+<span id="LC1402" class="line" lang="haskell"><span class="cm" style="color: #998; font-style: italic;">as we're really trying to solve for equirecursive type equality. Bottom</span></span>
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<td class="new_line diff-line-num new" data-linenumber="1403" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #c7f0d2; border-right-style: solid; padding: inherit;" align="right" bgcolor="#ddfbe6">
1403
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<td class="line_content new" style="padding: inherit;" bgcolor="#ecfdf0"><pre style='display: block; font-size: 0.8125rem; color: #303030; position: relative; font-family: "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dbdbdb;'>+<span id="LC1403" class="line" lang="haskell"><span class="cm" style="color: #998; font-style: italic;">line for users: recursive newtypes are dangerous.</span></span>
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1373
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<td class="new_line diff-line-num" data-linenumber="1404" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #f0f0f0; border-right-style: solid; padding: inherit;" align="right" bgcolor="#fafafa">
1404
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<td class="line_content" style="padding: inherit;"><pre style='display: block; font-size: 0.8125rem; color: #303030; position: relative; font-family: "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dbdbdb;'> <span id="LC1404" class="line" lang="haskell"></span>
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<td class="old_line diff-line-num" data-linenumber="1374" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #f0f0f0; border-right-style: solid; padding: inherit;" align="right" bgcolor="#fafafa">
1374
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<td class="new_line diff-line-num" data-linenumber="1405" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #f0f0f0; border-right-style: solid; padding: inherit;" align="right" bgcolor="#fafafa">
1405
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<td class="line_content" style="padding: inherit;"><pre style='display: block; font-size: 0.8125rem; color: #303030; position: relative; font-family: "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dbdbdb;'> <span id="LC1405" class="line" lang="haskell"><span class="cm" style="color: #998; font-style: italic;">Note [Eager reflexivity check]</span></span>
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1375
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1406
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<td class="line_content" style="padding: inherit;"><pre style='display: block; font-size: 0.8125rem; color: #303030; position: relative; font-family: "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dbdbdb;'> <span id="LC1406" class="line" lang="haskell"><span class="cm" style="color: #998; font-style: italic;">~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~</span></span>
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<a href="https://gitlab.haskell.org/ghc/ghc/-/commit/efe7c324435dfabf1ec64088fc9d10e0f1c0a0db#528aacc312e31d522c6e47247763aedb807caeec" style="color: #1068bf;"><strong style="font-weight: bold;">compiler/GHC/Tc/Solver/Rewrite.hs</strong></a>
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<td class="diff-line-num unfold js-unfold old_line" data-linenumber="497" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #f0f0f0; border-right-style: solid; padding: inherit;" align="right" bgcolor="#fafafa">...</td>
<td class="diff-line-num unfold js-unfold new_line" data-linenumber="497" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #f0f0f0; border-right-style: solid; padding: inherit;" align="right" bgcolor="#fafafa">...</td>
<td class="line_content match" style="color: rgba(0,0,0,0.3); padding: inherit;" bgcolor="#fafafa">@@ -497,6 +497,7 @@ rewrite_one ty@(TyConApp tc tys)</td>
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497
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<td class="new_line diff-line-num" data-linenumber="497" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #f0f0f0; border-right-style: solid; padding: inherit;" align="right" bgcolor="#fafafa">
497
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<td class="line_content" style="padding: inherit;"><pre style='display: block; font-size: 0.8125rem; color: #303030; position: relative; font-family: "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dbdbdb;'> <span id="LC497" class="line" lang="haskell"> <span class="c1" style="color: #998; font-style: italic;">-- NB: try rewrite_newtype_app even when tc isn't a newtype;</span></span>
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<td class="old_line diff-line-num" data-linenumber="498" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #f0f0f0; border-right-style: solid; padding: inherit;" align="right" bgcolor="#fafafa">
498
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<td class="new_line diff-line-num" data-linenumber="498" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #f0f0f0; border-right-style: solid; padding: inherit;" align="right" bgcolor="#fafafa">
498
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<td class="line_content" style="padding: inherit;"><pre style='display: block; font-size: 0.8125rem; color: #303030; position: relative; font-family: "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dbdbdb;'> <span id="LC498" class="line" lang="haskell"> <span class="c1" style="color: #998; font-style: italic;">-- the allows the possibility of having a newtype buried under</span></span>
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499
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499
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<td class="line_content" style="padding: inherit;"><pre style='display: block; font-size: 0.8125rem; color: #303030; position: relative; font-family: "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dbdbdb;'> <span id="LC499" class="line" lang="haskell"> <span class="c1" style="color: #998; font-style: italic;">-- a synonym. Needed for e.g. T12067.</span></span>
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<td class="old_line diff-line-num new" data-linenumber="500" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #c7f0d2; border-right-style: solid; padding: inherit;" align="right" bgcolor="#ddfbe6">
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<td class="new_line diff-line-num new" data-linenumber="500" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #c7f0d2; border-right-style: solid; padding: inherit;" align="right" bgcolor="#ddfbe6">
500
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<td class="line_content new" style="padding: inherit;" bgcolor="#ecfdf0"><pre style='display: block; font-size: 0.8125rem; color: #303030; position: relative; font-family: "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dbdbdb;'>+<span id="LC500" class="line" lang="haskell"> <span class="c1" style="color: #998; font-style: italic;">-- See Note [Unwrap newtypes first] in GHC.Tc.Solver.Canonincal.</span></span>
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500
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<td class="new_line diff-line-num" data-linenumber="501" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #f0f0f0; border-right-style: solid; padding: inherit;" align="right" bgcolor="#fafafa">
501
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<td class="line_content" style="padding: inherit;"><pre style='display: block; font-size: 0.8125rem; color: #303030; position: relative; font-family: "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dbdbdb;'> <span id="LC501" class="line" lang="haskell"> <span class="kr" style="font-weight: 600;">then</span> <span class="n" style="color: #333;">rewrite_newtype_app</span> <span class="n" style="color: #333;">ty</span></span>
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501
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<td class="new_line diff-line-num" data-linenumber="502" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #f0f0f0; border-right-style: solid; padding: inherit;" align="right" bgcolor="#fafafa">
502
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<td class="line_content" style="padding: inherit;"><pre style='display: block; font-size: 0.8125rem; color: #303030; position: relative; font-family: "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dbdbdb;'> <span id="LC502" class="line" lang="haskell"></span>
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502
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<td class="new_line diff-line-num" data-linenumber="503" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #f0f0f0; border-right-style: solid; padding: inherit;" align="right" bgcolor="#fafafa">
503
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<td class="line_content" style="padding: inherit;"><pre style='display: block; font-size: 0.8125rem; color: #303030; position: relative; font-family: "Menlo", "DejaVu Sans Mono", "Liberation Mono", "Consolas", "Ubuntu Mono", "Courier New", "andale mono", "lucida console", monospace; word-break: break-all; word-wrap: break-word; background-color: inherit; border-radius: 2px; margin: 0; padding: 0; border: inherit solid #dbdbdb;'> <span id="LC503" class="line" lang="haskell"> <span class="c1" style="color: #998; font-style: italic;">-- For * a normal data type application</span></span>
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