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% (c) The University of Glasgow 2006
% (c) The AQUA Project, Glasgow University, 1993-1998
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\section[TcDefaults]{Typechecking \tr{default} declarations}
\begin{code}
<pre><a name="line-1"></a><span class='hs-keyword'>module</span> <span class='hs-conid'>TcDefaults</span> <span class='hs-layout'>(</span> <span class='hs-varid'>tcDefaults</span> <span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-2"></a>
<a name="line-3"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>HsSyn</span>
<a name="line-4"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Name</span>
<a name="line-5"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Class</span>
<a name="line-6"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>TcRnMonad</span>
<a name="line-7"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>TcEnv</span>
<a name="line-8"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>TcHsType</span>
<a name="line-9"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>TcSimplify</span>
<a name="line-10"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>TcType</span>
<a name="line-11"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>PrelNames</span>
<a name="line-12"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>DynFlags</span>
<a name="line-13"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>SrcLoc</span>
<a name="line-14"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Data</span><span class='hs-varop'>.</span><span class='hs-conid'>Maybe</span>
<a name="line-15"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Outputable</span>
<a name="line-16"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>FastString</span>
</pre>\end{code}
\begin{code}
<pre><a name="line-1"></a><a name="tcDefaults"></a><span class='hs-definition'>tcDefaults</span> <span class='hs-keyglyph'>::</span> <span class='hs-keyglyph'>[</span><span class='hs-conid'>LDefaultDecl</span> <span class='hs-conid'>Name</span><span class='hs-keyglyph'>]</span>
<a name="line-2"></a> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>TcM</span> <span class='hs-layout'>(</span><span class='hs-conid'>Maybe</span> <span class='hs-keyglyph'>[</span><span class='hs-conid'>Type</span><span class='hs-keyglyph'>]</span><span class='hs-layout'>)</span> <span class='hs-comment'>-- Defaulting types to heave</span>
<a name="line-3"></a> <span class='hs-comment'>-- into Tc monad for later use</span>
<a name="line-4"></a> <span class='hs-comment'>-- in Disambig.</span>
<a name="line-5"></a>
<a name="line-6"></a><span class='hs-definition'>tcDefaults</span> <span class='hs-conid'>[]</span>
<a name="line-7"></a> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>getDeclaredDefaultTys</span> <span class='hs-comment'>-- No default declaration, so get the</span>
<a name="line-8"></a> <span class='hs-comment'>-- default types from the envt; </span>
<a name="line-9"></a> <span class='hs-comment'>-- i.e. use the curent ones</span>
<a name="line-10"></a> <span class='hs-comment'>-- (the caller will put them back there)</span>
<a name="line-11"></a> <span class='hs-comment'>-- It's important not to return defaultDefaultTys here (which</span>
<a name="line-12"></a> <span class='hs-comment'>-- we used to do) because in a TH program, tcDefaults [] is called</span>
<a name="line-13"></a> <span class='hs-comment'>-- repeatedly, once for each group of declarations between top-level</span>
<a name="line-14"></a> <span class='hs-comment'>-- splices. We don't want to carefully set the default types in</span>
<a name="line-15"></a> <span class='hs-comment'>-- one group, only for the next group to ignore them and install</span>
<a name="line-16"></a> <span class='hs-comment'>-- defaultDefaultTys</span>
<a name="line-17"></a>
<a name="line-18"></a><span class='hs-definition'>tcDefaults</span> <span class='hs-keyglyph'>[</span><span class='hs-conid'>L</span> <span class='hs-keyword'>_</span> <span class='hs-layout'>(</span><span class='hs-conid'>DefaultDecl</span> <span class='hs-conid'>[]</span><span class='hs-layout'>)</span><span class='hs-keyglyph'>]</span>
<a name="line-19"></a> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>return</span> <span class='hs-layout'>(</span><span class='hs-conid'>Just</span> <span class='hs-conid'>[]</span><span class='hs-layout'>)</span> <span class='hs-comment'>-- Default declaration specifying no types</span>
<a name="line-20"></a>
<a name="line-21"></a><span class='hs-definition'>tcDefaults</span> <span class='hs-keyglyph'>[</span><span class='hs-conid'>L</span> <span class='hs-varid'>locn</span> <span class='hs-layout'>(</span><span class='hs-conid'>DefaultDecl</span> <span class='hs-varid'>mono_tys</span><span class='hs-layout'>)</span><span class='hs-keyglyph'>]</span>
<a name="line-22"></a> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>setSrcSpan</span> <span class='hs-varid'>locn</span> <span class='hs-varop'>$</span>
<a name="line-23"></a> <span class='hs-varid'>addErrCtxt</span> <span class='hs-varid'>defaultDeclCtxt</span> <span class='hs-varop'>$</span>
<a name="line-24"></a> <span class='hs-keyword'>do</span> <span class='hs-layout'>{</span> <span class='hs-varid'>ovl_str</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>doptM</span> <span class='hs-conid'>Opt_OverloadedStrings</span>
<a name="line-25"></a> <span class='hs-layout'>;</span> <span class='hs-varid'>num_class</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>tcLookupClass</span> <span class='hs-varid'>numClassName</span>
<a name="line-26"></a> <span class='hs-layout'>;</span> <span class='hs-varid'>is_str_class</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>tcLookupClass</span> <span class='hs-varid'>isStringClassName</span>
<a name="line-27"></a> <span class='hs-layout'>;</span> <span class='hs-keyword'>let</span> <span class='hs-varid'>deflt_clss</span> <span class='hs-keyglyph'>|</span> <span class='hs-varid'>ovl_str</span> <span class='hs-keyglyph'>=</span> <span class='hs-keyglyph'>[</span><span class='hs-varid'>num_class</span><span class='hs-layout'>,</span> <span class='hs-varid'>is_str_class</span><span class='hs-keyglyph'>]</span>
<a name="line-28"></a> <span class='hs-keyglyph'>|</span> <span class='hs-varid'>otherwise</span> <span class='hs-keyglyph'>=</span> <span class='hs-keyglyph'>[</span><span class='hs-varid'>num_class</span><span class='hs-keyglyph'>]</span>
<a name="line-29"></a>
<a name="line-30"></a> <span class='hs-layout'>;</span> <span class='hs-varid'>tau_tys</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>mapM</span> <span class='hs-layout'>(</span><span class='hs-varid'>tc_default_ty</span> <span class='hs-varid'>deflt_clss</span><span class='hs-layout'>)</span> <span class='hs-varid'>mono_tys</span>
<a name="line-31"></a>
<a name="line-32"></a> <span class='hs-layout'>;</span> <span class='hs-varid'>return</span> <span class='hs-layout'>(</span><span class='hs-conid'>Just</span> <span class='hs-varid'>tau_tys</span><span class='hs-layout'>)</span> <span class='hs-layout'>}</span>
<a name="line-33"></a>
<a name="line-34"></a><span class='hs-definition'>tcDefaults</span> <span class='hs-varid'>decls</span><span class='hs-keyglyph'>@</span><span class='hs-layout'>(</span><span class='hs-conid'>L</span> <span class='hs-varid'>locn</span> <span class='hs-layout'>(</span><span class='hs-conid'>DefaultDecl</span> <span class='hs-keyword'>_</span><span class='hs-layout'>)</span> <span class='hs-conop'>:</span> <span class='hs-keyword'>_</span><span class='hs-layout'>)</span>
<a name="line-35"></a> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>setSrcSpan</span> <span class='hs-varid'>locn</span> <span class='hs-varop'>$</span>
<a name="line-36"></a> <span class='hs-varid'>failWithTc</span> <span class='hs-layout'>(</span><span class='hs-varid'>dupDefaultDeclErr</span> <span class='hs-varid'>decls</span><span class='hs-layout'>)</span>
<a name="line-37"></a>
<a name="line-38"></a>
<a name="line-39"></a><a name="tc_default_ty"></a><span class='hs-definition'>tc_default_ty</span> <span class='hs-keyglyph'>::</span> <span class='hs-keyglyph'>[</span><span class='hs-conid'>Class</span><span class='hs-keyglyph'>]</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>LHsType</span> <span class='hs-conid'>Name</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>TcM</span> <span class='hs-conid'>Type</span>
<a name="line-40"></a><span class='hs-definition'>tc_default_ty</span> <span class='hs-varid'>deflt_clss</span> <span class='hs-varid'>hs_ty</span>
<a name="line-41"></a> <span class='hs-keyglyph'>=</span> <span class='hs-keyword'>do</span> <span class='hs-layout'>{</span> <span class='hs-varid'>ty</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>tcHsSigType</span> <span class='hs-conid'>DefaultDeclCtxt</span> <span class='hs-varid'>hs_ty</span>
<a name="line-42"></a> <span class='hs-layout'>;</span> <span class='hs-varid'>checkTc</span> <span class='hs-layout'>(</span><span class='hs-varid'>isTauTy</span> <span class='hs-varid'>ty</span><span class='hs-layout'>)</span> <span class='hs-layout'>(</span><span class='hs-varid'>polyDefErr</span> <span class='hs-varid'>hs_ty</span><span class='hs-layout'>)</span>
<a name="line-43"></a>
<a name="line-44"></a> <span class='hs-comment'>-- Check that the type is an instance of at least one of the deflt_clss</span>
<a name="line-45"></a> <span class='hs-layout'>;</span> <span class='hs-varid'>oks</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>mapM</span> <span class='hs-layout'>(</span><span class='hs-varid'>check_instance</span> <span class='hs-varid'>ty</span><span class='hs-layout'>)</span> <span class='hs-varid'>deflt_clss</span>
<a name="line-46"></a> <span class='hs-layout'>;</span> <span class='hs-varid'>checkTc</span> <span class='hs-layout'>(</span><span class='hs-varid'>or</span> <span class='hs-varid'>oks</span><span class='hs-layout'>)</span> <span class='hs-layout'>(</span><span class='hs-varid'>badDefaultTy</span> <span class='hs-varid'>ty</span> <span class='hs-varid'>deflt_clss</span><span class='hs-layout'>)</span>
<a name="line-47"></a> <span class='hs-layout'>;</span> <span class='hs-varid'>return</span> <span class='hs-varid'>ty</span> <span class='hs-layout'>}</span>
<a name="line-48"></a>
<a name="line-49"></a><a name="check_instance"></a><span class='hs-definition'>check_instance</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>Type</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>Class</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>TcM</span> <span class='hs-conid'>Bool</span>
<a name="line-50"></a> <span class='hs-comment'>-- Check that ty is an instance of cls</span>
<a name="line-51"></a> <span class='hs-comment'>-- We only care about whether it worked or not; return a boolean</span>
<a name="line-52"></a><span class='hs-definition'>check_instance</span> <span class='hs-varid'>ty</span> <span class='hs-varid'>cls</span>
<a name="line-53"></a> <span class='hs-keyglyph'>=</span> <span class='hs-keyword'>do</span> <span class='hs-layout'>{</span> <span class='hs-layout'>(</span><span class='hs-keyword'>_</span><span class='hs-layout'>,</span> <span class='hs-varid'>mb_res</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>tryTc</span> <span class='hs-layout'>(</span><span class='hs-varid'>tcSimplifyDefault</span> <span class='hs-keyglyph'>[</span><span class='hs-varid'>mkClassPred</span> <span class='hs-varid'>cls</span> <span class='hs-keyglyph'>[</span><span class='hs-varid'>ty</span><span class='hs-keyglyph'>]</span><span class='hs-keyglyph'>]</span><span class='hs-layout'>)</span>
<a name="line-54"></a> <span class='hs-layout'>;</span> <span class='hs-varid'>return</span> <span class='hs-layout'>(</span><span class='hs-varid'>isJust</span> <span class='hs-varid'>mb_res</span><span class='hs-layout'>)</span> <span class='hs-layout'>}</span>
<a name="line-55"></a>
<a name="line-56"></a><a name="defaultDeclCtxt"></a><span class='hs-definition'>defaultDeclCtxt</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>SDoc</span>
<a name="line-57"></a><span class='hs-definition'>defaultDeclCtxt</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>ptext</span> <span class='hs-layout'>(</span><span class='hs-varid'>sLit</span> <span class='hs-str'>"When checking the types in a default declaration"</span><span class='hs-layout'>)</span>
<a name="line-58"></a>
<a name="line-59"></a><a name="dupDefaultDeclErr"></a><span class='hs-definition'>dupDefaultDeclErr</span> <span class='hs-keyglyph'>::</span> <span class='hs-keyglyph'>[</span><span class='hs-conid'>Located</span> <span class='hs-layout'>(</span><span class='hs-conid'>DefaultDecl</span> <span class='hs-conid'>Name</span><span class='hs-layout'>)</span><span class='hs-keyglyph'>]</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>SDoc</span>
<a name="line-60"></a><span class='hs-definition'>dupDefaultDeclErr</span> <span class='hs-layout'>(</span><span class='hs-conid'>L</span> <span class='hs-keyword'>_</span> <span class='hs-layout'>(</span><span class='hs-conid'>DefaultDecl</span> <span class='hs-keyword'>_</span><span class='hs-layout'>)</span> <span class='hs-conop'>:</span> <span class='hs-varid'>dup_things</span><span class='hs-layout'>)</span>
<a name="line-61"></a> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>hang</span> <span class='hs-layout'>(</span><span class='hs-varid'>ptext</span> <span class='hs-layout'>(</span><span class='hs-varid'>sLit</span> <span class='hs-str'>"Multiple default declarations"</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span>
<a name="line-62"></a> <span class='hs-num'>4</span> <span class='hs-layout'>(</span><span class='hs-varid'>vcat</span> <span class='hs-layout'>(</span><span class='hs-varid'>map</span> <span class='hs-varid'>pp</span> <span class='hs-varid'>dup_things</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span>
<a name="line-63"></a> <span class='hs-keyword'>where</span>
<a name="line-64"></a> <span class='hs-varid'>pp</span> <span class='hs-layout'>(</span><span class='hs-conid'>L</span> <span class='hs-varid'>locn</span> <span class='hs-layout'>(</span><span class='hs-conid'>DefaultDecl</span> <span class='hs-keyword'>_</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>ptext</span> <span class='hs-layout'>(</span><span class='hs-varid'>sLit</span> <span class='hs-str'>"here was another default declaration"</span><span class='hs-layout'>)</span> <span class='hs-varop'><+></span> <span class='hs-varid'>ppr</span> <span class='hs-varid'>locn</span>
<a name="line-65"></a><span class='hs-definition'>dupDefaultDeclErr</span> <span class='hs-conid'>[]</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>panic</span> <span class='hs-str'>"dupDefaultDeclErr []"</span>
<a name="line-66"></a>
<a name="line-67"></a><a name="polyDefErr"></a><span class='hs-definition'>polyDefErr</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>LHsType</span> <span class='hs-conid'>Name</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>SDoc</span>
<a name="line-68"></a><span class='hs-definition'>polyDefErr</span> <span class='hs-varid'>ty</span>
<a name="line-69"></a> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>hang</span> <span class='hs-layout'>(</span><span class='hs-varid'>ptext</span> <span class='hs-layout'>(</span><span class='hs-varid'>sLit</span> <span class='hs-str'>"Illegal polymorphic type in default declaration"</span><span class='hs-layout'>)</span> <span class='hs-varop'><></span> <span class='hs-varid'>colon</span><span class='hs-layout'>)</span> <span class='hs-num'>4</span> <span class='hs-layout'>(</span><span class='hs-varid'>ppr</span> <span class='hs-varid'>ty</span><span class='hs-layout'>)</span>
<a name="line-70"></a>
<a name="line-71"></a><a name="badDefaultTy"></a><span class='hs-definition'>badDefaultTy</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>Type</span> <span class='hs-keyglyph'>-></span> <span class='hs-keyglyph'>[</span><span class='hs-conid'>Class</span><span class='hs-keyglyph'>]</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>SDoc</span>
<a name="line-72"></a><span class='hs-definition'>badDefaultTy</span> <span class='hs-varid'>ty</span> <span class='hs-varid'>deflt_clss</span>
<a name="line-73"></a> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>hang</span> <span class='hs-layout'>(</span><span class='hs-varid'>ptext</span> <span class='hs-layout'>(</span><span class='hs-varid'>sLit</span> <span class='hs-str'>"The default type"</span><span class='hs-layout'>)</span> <span class='hs-varop'><+></span> <span class='hs-varid'>quotes</span> <span class='hs-layout'>(</span><span class='hs-varid'>ppr</span> <span class='hs-varid'>ty</span><span class='hs-layout'>)</span> <span class='hs-varop'><+></span> <span class='hs-varid'>ptext</span> <span class='hs-layout'>(</span><span class='hs-varid'>sLit</span> <span class='hs-str'>"is not an instance of"</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span>
<a name="line-74"></a> <span class='hs-num'>2</span> <span class='hs-layout'>(</span><span class='hs-varid'>foldr1</span> <span class='hs-layout'>(</span><span class='hs-keyglyph'>\</span><span class='hs-varid'>a</span> <span class='hs-varid'>b</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>a</span> <span class='hs-varop'><+></span> <span class='hs-varid'>ptext</span> <span class='hs-layout'>(</span><span class='hs-varid'>sLit</span> <span class='hs-str'>"or"</span><span class='hs-layout'>)</span> <span class='hs-varop'><+></span> <span class='hs-varid'>b</span><span class='hs-layout'>)</span> <span class='hs-layout'>(</span><span class='hs-varid'>map</span> <span class='hs-layout'>(</span><span class='hs-varid'>quotes</span><span class='hs-varop'>.</span> <span class='hs-varid'>ppr</span><span class='hs-layout'>)</span> <span class='hs-varid'>deflt_clss</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span>
</pre>\end{code}
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