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GitLab

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<h3>

 Marge Bot pushed to branch master

at <a href="https://gitlab.haskell.org/ghc/ghc">Glasgow Haskell Compiler / GHC</a>

</h3>

<h4>

Commits:

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<li>

<strong><a href="https://gitlab.haskell.org/ghc/ghc/-/commit/4cab68974dba3e674016514c939946ce60e58273">4cab6897</a></strong>

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<span>by Adam Sandberg Ericsson</span>

<i>at 2020-06-17T15:32:44-04:00</i>

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<pre class="commit-message" style="white-space: pre-wrap; margin: 0;">docs: fix formatting in users guide

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<h4>5 changed files:</h4>

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<a href="#b421960e854c6cfa1e4ca830bd6a5fc6eef91168">

docs/users_guide/8.12.1-notes.rst

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<a href="#616606d7ec92f17c847240a7bc125e1d8c9c00a1">

docs/users_guide/extending_ghc.rst

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<a href="#afd1105d8e32dc50acf9fc381b4433a3bcd009cf">

docs/users_guide/exts/explicit_forall.rst

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<a href="#0cc784483e34410e9b43b5cfc23ee304faba81d1">

docs/users_guide/exts/gadt_syntax.rst

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<a href="#e16ae6db99f98868d3603a0c7df0bb6a793a330d">

docs/users_guide/using-warnings.rst

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<h4>Changes:</h4>

<li id="b421960e854c6cfa1e4ca830bd6a5fc6eef91168">

<a href="https://gitlab.haskell.org/ghc/ghc/-/commit/4cab68974dba3e674016514c939946ce60e58273#b421960e854c6cfa1e4ca830bd6a5fc6eef91168"><strong>docs/users_guide/8.12.1-notes.rst</strong></a>

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<pre style="margin: 0;"> <span id="LC21" class="line" lang="plaintext"></span>

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<pre style="margin: 0;"> <span id="LC22" class="line" lang="plaintext">* Pattern-Match Coverage Checking</span>

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<pre style="margin: 0;"> <span id="LC23" class="line" lang="plaintext"></span>

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<pre style="margin: 0;">-<span id="LC24" class="line" lang="plaintext">  - The revamp of the pattern-match coverage checker that started in 8.10 concludes with this release and implements the<span class="idiff left right"> </span></span>

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<pre style="margin: 0;">+<span id="LC24" class="line" lang="plaintext">  - The revamp of the pattern-match coverage checker that started in 8.10 concludes with this release and implements the</span>

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<pre style="margin: 0;"> <span id="LC25" class="line" lang="plaintext">    novel `*Lower Your Guards* <https://www.microsoft.com/en-us/research/uploads/prod/2020/03/lyg.pdf>`_ algorithm.</span>

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<pre style="margin: 0;">-<span id="LC26" class="line" lang="plaintext">  - Compared to 8.10, end users might notice improvements to "long-distance information": ::<span class="idiff left right"> haskell</span></span>

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<pre style="margin: 0;">+<span id="LC26" class="line" lang="plaintext">  - Compared to 8.10, end users might notice improvements to "long-distance information": ::</span>

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<pre style="margin: 0;"> <span id="LC27" class="line" lang="plaintext"></span>

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<pre style="margin: 0;">-<span id="LC28" class="line" lang="plaintext">      :linenos:   </span>

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<pre style="margin: 0;"> <span id="LC28" class="line" lang="plaintext">      f True = 1</span>

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<pre style="margin: 0;"> <span id="LC29" class="line" lang="plaintext">      f x    = ... case x of { False -> 2; True -> 3 } ...</span>

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<pre style="margin: 0;"> <span id="LC30" class="line" lang="plaintext"></span>

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<pre style="margin: 0;"> <span id="LC124" class="line" lang="plaintext">      MkT2 :: (forall a. a -> T)</span>

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<pre style="margin: 0;"> <span id="LC125" class="line" lang="plaintext"></span>

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<td class="diff-line-num old_line" data-linenumber="127" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #f0f0f0; border-right-style: solid; padding: 0 5px;" align="right" bgcolor="#fafafa">

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<pre style="margin: 0;"> <span id="LC126" class="line" lang="plaintext">  ``MkT1`` and ``MkT2`` are rejected because the lack of an outermost</span>

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<pre style="margin: 0;">-<span id="LC128" class="line" lang="plaintext">  ``forall`` triggers implicit quantification, making the explicit ``forall``s</span>

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<pre style="margin: 0;">+<span id="LC127" class="line" lang="plaintext">  ``forall`` triggers implicit quantification, making the explicit ``forall``<span class="idiff left right">\ </span>s</span>

</pre>

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129

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<pre style="margin: 0;"> <span id="LC128" class="line" lang="plaintext">  nested. Furthermore, GADT constructors do not permit the use of nested</span>

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<pre style="margin: 0;">-<span id="LC130" class="line" lang="plaintext">  ``forall``s, as explained in :ref:`formal-gadt-syntax`.</span>

</pre>

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<pre style="margin: 0;">+<span id="LC129" class="line" lang="plaintext">  ``forall``<span class="idiff left right">\ </span>s, as explained in :ref:`formal-gadt-syntax`.</span>

</pre>

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<pre style="margin: 0;"> <span id="LC130" class="line" lang="plaintext"></span>

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<pre style="margin: 0;">-<span id="LC132" class="line" lang="plaintext">  In addition to rejecting nested ``forall``s, GHC is now more stringent about</span>

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<pre style="margin: 0;">+<span id="LC131" class="line" lang="plaintext">  In addition to rejecting nested ``forall``<span class="idiff left right">\ </span>s, GHC is now more stringent about</span>

</pre>

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<pre style="margin: 0;"> <span id="LC132" class="line" lang="plaintext">  rejecting uses of nested *contexts* in GADT constructors. For example, the</span>

</pre>

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<pre style="margin: 0;"> <span id="LC133" class="line" lang="plaintext">  following example, which previous versions of GHC would accept, is now</span>

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<pre style="margin: 0;">-<span id="LC135" class="line" lang="plaintext">  rejected:</span>

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<pre style="margin: 0;">+<span id="LC134" class="line" lang="plaintext">  rejected:<span class="idiff left right"> ::</span></span>

</pre>

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<pre style="margin: 0;"> <span id="LC135" class="line" lang="plaintext"></span>

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<pre style="margin: 0;"> <span id="LC136" class="line" lang="plaintext">    data U a where</span>

</pre>

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<td class="diff-line-num old_line" data-linenumber="138" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #f0f0f0; border-right-style: solid; padding: 0 5px;" align="right" bgcolor="#fafafa">

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<pre style="margin: 0;"> <span id="LC137" class="line" lang="plaintext">      MkU :: (Show a => U a)</span>

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</li>

<li id="616606d7ec92f17c847240a7bc125e1d8c9c00a1">

<a href="https://gitlab.haskell.org/ghc/ghc/-/commit/4cab68974dba3e674016514c939946ce60e58273#616606d7ec92f17c847240a7bc125e1d8c9c00a1"><strong>docs/users_guide/extending_ghc.rst</strong></a>

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<td class="line_content match " style="padding-left: 0.5em; padding-right: 0.5em; color: rgba(0,0,0,0.3);" bgcolor="#fafafa">@@ -775,7 +775,7 @@ each case:</td>

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<pre style="margin: 0;"> <span id="LC775" class="line" lang="mosel"><span class="s1" style="color: #d14;">    package/field-n</span></span>

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<pre style="margin: 0;"> <span id="LC776" class="line" lang="mosel"></span>

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<pre style="margin: 0;"> <span id="LC777" class="line" lang="mosel"><span class="s1" style="color: #d14;">To read an interface file from an external tool without linking to GHC, the format</span></span>

</pre>

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778

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<td class="diff-line-num new_line old" data-linenumber="778" style="width: 35px; color: rgba(0,0,0,0.3); border-right-width: 1px; border-right-color: #fac5cd; border-right-style: solid; padding: 0 5px;" align="right" bgcolor="#f9d7dc">

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<pre style="margin: 0;">-<span id="LC778" class="line" lang="mosel"><span class="s1" style="color: #d14;">is described at `Extensible Interface Files<https://gitlab.haskell.org/ghc/ghc/wikis/Extensible-Interface-Files>`_.</span></span>

</pre>

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<pre style="margin: 0;">+<span id="LC778" class="line" lang="mosel"><span class="s1" style="color: #d14;">is described at `Extensible Interface Files<span class="idiff left right"> </span><https://gitlab.haskell.org/ghc/ghc/wikis/Extensible-Interface-Files>`_.</span></span>

</pre>

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<pre style="margin: 0;"> <span id="LC780" class="line" lang="mosel"><span class="s1" style="color: #d14;">Source plugin example</span></span>

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<pre style="margin: 0;"> <span id="LC781" class="line" lang="mosel"><span class="s1" style="color: #d14;">^^^^^^^^^^^^^^^^^^^^^</span></span>

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<li id="afd1105d8e32dc50acf9fc381b4433a3bcd009cf">

<a href="https://gitlab.haskell.org/ghc/ghc/-/commit/4cab68974dba3e674016514c939946ce60e58273#afd1105d8e32dc50acf9fc381b4433a3bcd009cf"><strong>docs/users_guide/exts/explicit_forall.rst</strong></a>

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<pre style="margin: 0;"> <span id="LC112" class="line" lang="plaintext"></span>

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<pre style="margin: 0;"> <span id="LC113" class="line" lang="plaintext">    {-# RULES "f" forall (g :: forall a. a -> b) x. f g x = g x :: b #-}</span>

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<pre style="margin: 0;"> <span id="LC114" class="line" lang="plaintext"></span>

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<pre style="margin: 0;">-<span id="LC115" class="line" lang="plaintext">- GADT constructors are extra particular about their ``forall``s. In addition</span>

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<pre style="margin: 0;">+<span id="LC115" class="line" lang="plaintext">- GADT constructors are extra particular about their ``forall``<span class="idiff left right">\ </span>s. In addition</span>

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<pre style="margin: 0;"> <span id="LC116" class="line" lang="plaintext">  to adhering to the ``forall``-or-nothing rule, GADT constructors also forbid</span>

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<pre style="margin: 0;">-<span id="LC117" class="line" lang="plaintext">  nested ``forall``s. For example, GHC would reject the following GADT: ::</span>

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<pre style="margin: 0;">+<span id="LC117" class="line" lang="plaintext">  nested ``forall``<span class="idiff left right">\ </span>s. For example, GHC would reject the following GADT: ::</span>

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<pre style="margin: 0;"> <span id="LC118" class="line" lang="plaintext"></span>

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<pre style="margin: 0;"> <span id="LC119" class="line" lang="plaintext">    data T where</span>

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<pre style="margin: 0;"> <span id="LC120" class="line" lang="plaintext">      MkT :: (forall a. a -> b -> T)</span>

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<pre style="margin: 0;"> <span id="LC122" class="line" lang="plaintext">  Because of the lack of an outermost ``forall`` in the type of ``MkT``, the</span>

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<pre style="margin: 0;"> <span id="LC123" class="line" lang="plaintext">  ``b`` would be implicitly quantified. In effect, it would be as if one had</span>

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<pre style="margin: 0;"> <span id="LC124" class="line" lang="plaintext">  written ``MkT :: forall b. (forall a. a -> b -> T)``, which contains nested</span>

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<pre style="margin: 0;">-<span id="LC125" class="line" lang="plaintext">  ``forall``s. See :ref:`formal-gadt-syntax`.</span></pre>

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<pre style="margin: 0;">+<span id="LC125" class="line" lang="plaintext">  ``forall``<span class="idiff left right">\ </span>s. See :ref:`formal-gadt-syntax`.</span></pre>

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<li id="0cc784483e34410e9b43b5cfc23ee304faba81d1">

<a href="https://gitlab.haskell.org/ghc/ghc/-/commit/4cab68974dba3e674016514c939946ce60e58273#0cc784483e34410e9b43b5cfc23ee304faba81d1"><strong>docs/users_guide/exts/gadt_syntax.rst</strong></a>

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<td class="line_content match " style="padding-left: 0.5em; padding-right: 0.5em; color: rgba(0,0,0,0.3);" bgcolor="#fafafa">@@ -161,23 +161,23 @@ Where:</td>

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<pre style="margin: 0;"> <span id="LC161" class="line" lang="plaintext"></span>

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<pre style="margin: 0;"> <span id="LC162" class="line" lang="plaintext">- ``btype`` is a type that is not allowed to have an outermost</span>

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<pre style="margin: 0;"> <span id="LC163" class="line" lang="plaintext">  ``forall``/``=>`` unless it is surrounded by parentheses. For example,</span>

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<pre style="margin: 0;">-<span id="LC164" class="line" lang="plaintext">  ``forall a. a`` and ``Eq a => a`` are not legal ``btype``s, but</span>

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<pre style="margin: 0;">+<span id="LC164" class="line" lang="plaintext">  ``forall a. a`` and ``Eq a => a`` are not legal ``btype``<span class="idiff left right">\ </span>s, but</span>

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<pre style="margin: 0;"> <span id="LC165" class="line" lang="plaintext">  ``(forall a. a)`` and ``(Eq a => a)`` are legal.</span>

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<pre style="margin: 0;"> <span id="LC166" class="line" lang="plaintext">- ``ctype`` is a ``btype`` that has no restrictions on an outermost</span>

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<pre style="margin: 0;">-<span id="LC167" class="line" lang="plaintext">  ``forall``/``=>``, so ``forall a. a`` and ``Eq a => a`` are legal ``ctype``s.</span>

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<pre style="margin: 0;">-<span id="LC168" class="line" lang="plaintext">- ``return_type`` is a type that is not allowed to have ``forall``<span class="idiff left right">s, ``=>``</span>s,</span>

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<pre style="margin: 0;">-<span id="LC169" class="line" lang="plaintext">  or ``->``s.</span>

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<pre style="margin: 0;">+<span id="LC167" class="line" lang="plaintext">  ``forall``/``=>``, so ``forall a. a`` and ``Eq a => a`` are legal ``ctype``<span class="idiff left right">\ </span>s.</span>

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<pre style="margin: 0;">+<span id="LC168" class="line" lang="plaintext">- ``return_type`` is a type that is not allowed to have ``forall``<span class="idiff left right">\ s, ``=>``\ </span>s,</span>

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<pre style="margin: 0;">+<span id="LC169" class="line" lang="plaintext">  or ``->``<span class="idiff left right">\ </span>s.</span>

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<pre style="margin: 0;"> <span id="LC170" class="line" lang="plaintext"></span>

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<pre style="margin: 0;"> <span id="LC171" class="line" lang="plaintext">This is a simplified grammar that does not fully delve into all of the</span>

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<pre style="margin: 0;"> <span id="LC172" class="line" lang="plaintext">implementation details of GHC's parser (such as the placement of Haddock</span>

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<pre style="margin: 0;"> <span id="LC173" class="line" lang="plaintext">comments), but it is sufficient to attain an understanding of what is</span>

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<pre style="margin: 0;"> <span id="LC174" class="line" lang="plaintext">syntactically allowed. Some further various observations about this grammar:</span>

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<pre style="margin: 0;"> <span id="LC175" class="line" lang="plaintext"></span>

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<pre style="margin: 0;">-<span id="LC176" class="line" lang="plaintext">- GADT constructor types are currently not permitted to have nested ``forall``s</span>

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<pre style="margin: 0;">-<span id="LC177" class="line" lang="plaintext">  or ``=>``s. (e.g., something like ``MkT :: Int -> forall a. a -> T`` would be</span>

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<pre style="margin: 0;">+<span id="LC176" class="line" lang="plaintext">- GADT constructor types are currently not permitted to have nested ``forall``<span class="idiff left right">\ </span>s</span>

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<pre style="margin: 0;">+<span id="LC177" class="line" lang="plaintext">  or ``=>``<span class="idiff left right">\ </span>s. (e.g., something like ``MkT :: Int -> forall a. a -> T`` would be</span>

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<pre style="margin: 0;"> <span id="LC178" class="line" lang="plaintext">  rejected.) As a result, ``gadt_sig`` puts all of its quantification and</span>

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<pre style="margin: 0;"> <span id="LC179" class="line" lang="plaintext">  constraints up front with ``opt_forall`` and ``opt_context``. Note that</span>

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<pre style="margin: 0;">-<span id="LC180" class="line" lang="plaintext">  higher-rank ``forall``<span class="idiff left right">s and ``=>``</span>s are only permitted if they do not appear</span>

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<pre style="margin: 0;">+<span id="LC180" class="line" lang="plaintext">  higher-rank ``forall``<span class="idiff left right">\ s and ``=>``\ </span>s are only permitted if they do not appear</span>

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<pre style="margin: 0;"> <span id="LC181" class="line" lang="plaintext">  directly to the right of a function arrow in a `prefix_gadt_body`. (e.g.,</span>

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<pre style="margin: 0;"> <span id="LC182" class="line" lang="plaintext">  something like ``MkS :: Int -> (forall a. a) -> S`` is allowed, since</span>

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<pre style="margin: 0;"> <span id="LC183" class="line" lang="plaintext">  parentheses separate the ``forall`` from the ``->``.)</span>

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<li id="e16ae6db99f98868d3603a0c7df0bb6a793a330d">

<a href="https://gitlab.haskell.org/ghc/ghc/-/commit/4cab68974dba3e674016514c939946ce60e58273#e16ae6db99f98868d3603a0c7df0bb6a793a330d"><strong>docs/users_guide/using-warnings.rst</strong></a>

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<pre style="margin: 0;"> <span id="LC239" class="line" lang="plaintext"></span>

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<pre style="margin: 0;"> <span id="LC240" class="line" lang="plaintext">     - ``Data.List`` due to the future addition of ``Data.List.singleton`` and</span>

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<pre style="margin: 0;"> <span id="LC241" class="line" lang="plaintext">       specialisation of exports to the ``[]`` type. See the</span>

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<pre style="margin: 0;">-<span id="LC242" class="line" lang="plaintext">       :ref:`mailing list</span>

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<pre style="margin: 0;">-<span id="LC243" class="line" lang="plaintext">       <https://groups.google.com/forum/#!topic/haskell-core-libraries/q3zHLmzBa5E>`</span>

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<pre style="margin: 0;">+<span id="LC242" class="line" lang="plaintext">       `mailing list <https://groups.google.com/forum/#!topic/haskell-core-libraries/q3zHLmzBa5E>`_</span>

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<pre style="margin: 0;"> <span id="LC243" class="line" lang="plaintext">       for details.</span>

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<pre style="margin: 0;"> <span id="LC244" class="line" lang="plaintext"></span>

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<pre style="margin: 0;"> <span id="LC245" class="line" lang="plaintext">    This warning can be addressed by either adding an explicit import list or</span>

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