Better documentation for -XLiberalTypeSynonyms, and steal forall keyword

In my travels through the front end I discoverd that -XLiberalTypeSynonyms is
rather thinly described.  Furthermore, it alleges that you can write a
forall on the RHS of a type synonym decl, so that means it should enable
the forall keyword.

diff --git a/compiler/parser/Lexer.x b/compiler/parser/Lexer.x
index f06624e..66f4fe5 100644 (file)
--- a/compiler/parser/Lexer.x
+++ b/compiler/parser/Lexer.x
@@ -1665,6 +1665,7 @@ mkPState buf loc flags  =
               .|. qqBit        `setBitIf` dopt Opt_QuasiQuotes flags
               .|. ipBit        `setBitIf` dopt Opt_ImplicitParams flags
               .|. explicitForallBit `setBitIf` dopt Opt_ScopedTypeVariables flags
+              .|. explicitForallBit `setBitIf` dopt Opt_LiberalTypeSynonyms flags
               .|. explicitForallBit `setBitIf` dopt Opt_PolymorphicComponents flags
               .|. explicitForallBit `setBitIf` dopt Opt_ExistentialQuantification flags
               .|. explicitForallBit `setBitIf` dopt Opt_Rank2Types flags

diff --git a/docs/users_guide/glasgow_exts.xml b/docs/users_guide/glasgow_exts.xml
index 4d31dd1..cb5033a 100644 (file)
--- a/docs/users_guide/glasgow_exts.xml
+++ b/docs/users_guide/glasgow_exts.xml
@@ -164,6 +164,38 @@ documentation</ulink> describes all the libraries that come with GHC.
 
       <varlistentry>
        <term>
+          <option>-XRank2Types</option>
+          <indexterm><primary><option>-XRank2Types</option></primary></indexterm>
+        </term>
+       <term>
+          <option>-XRankNTypes</option>
+          <indexterm><primary><option>-XRankNTypes</option></primary></indexterm>
+        </term>
+       <term>
+          <option>-XPolymorphicComponents</option>
+          <indexterm><primary><option>-XPolymorphicComponents</option></primary></indexterm>
+        </term>
+       <listitem>
+         <para> These flags control higher-rank polymorphism.  
+           See <xref linkend="universal-quantification"/>.</para>
+         <para>New reserved words: <literal>forall</literal>.</para>
+       </listitem>
+      </varlistentry>
+
+      <varlistentry>
+       <term>
+          <option>-XLiberalTypeSynonyms</option>
+          <indexterm><primary><option>-XLiberalTypeSynonyms</option></primary></indexterm>
+        </term>
+       <listitem>
+         <para> Allow more liberal type synonyms.
+           See <xref linkend="type-synonyms"/>.</para>
+         <para>New reserved words: <literal>forall</literal>.</para>
+       </listitem>
+      </varlistentry>
+
+      <varlistentry>
+       <term>
           <option>-XOverlappingInstances</option>
           <indexterm><primary><option>-XOverlappingInstances</option></primary></indexterm>
         </term>
@@ -180,8 +212,7 @@ documentation</ulink> describes all the libraries that come with GHC.
           <indexterm><primary><option>-fcontext-stack</option></primary></indexterm>
         </term>
        <listitem>
-         <para> See <xref linkend="instance-decls"/>.  Only relevant
-          if you also use <option>-fglasgow-exts</option>.</para>
+         <para> See <xref linkend="instance-decls"/>. </para>
        </listitem>
       </varlistentry>
 
@@ -1716,9 +1747,12 @@ to be written infix, very much like expressions.  More specifically:
 <title>Liberalised type synonyms</title>
 
 <para>
-Type synonyms are like macros at the type level, and
+Type synonyms are like macros at the type level, but Haskell 98 imposes many rules
+on individual synonym declarations.
+With the <option>-XLiberalTypeSynonyms</option> extension,
 GHC does validity checking on types <emphasis>only after expanding type synonyms</emphasis>.
-That means that GHC can be very much more liberal about type synonyms than Haskell 98:
+That means that GHC can be very much more liberal about type synonyms than Haskell 98. 
+
 <itemizedlist>
 <listitem> <para>You can write a <literal>forall</literal> (including overloading)
 in a type synonym, thus:
@@ -1735,7 +1769,8 @@ in a type synonym, thus:
 </listitem>
 
 <listitem><para>
-You can write an unboxed tuple in a type synonym:
+If you also use <option>-XUnboxedTuples</option>, 
+you can write an unboxed tuple in a type synonym:
 <programlisting>
   type Pr = (# Int, Int #)