diff options
Diffstat (limited to 'docs/users_guide/using.xml')
| -rw-r--r-- | docs/users_guide/using.xml | 130 |
1 files changed, 77 insertions, 53 deletions
diff --git a/docs/users_guide/using.xml b/docs/users_guide/using.xml index 8d8211eb5a..921d5a3345 100644 --- a/docs/users_guide/using.xml +++ b/docs/users_guide/using.xml @@ -899,20 +899,37 @@ ghci> :set -fprint-explicit-foralls ghci> :t f f :: forall a. a -> a </screen> - Using <option>-fprint-explicit-kinds</option> makes GHC print kind-foralls and kind applications +However, regardless of the flag setting, the quantifiers are printed under these circumstances: +<itemizedlist> +<listitem><para>For nested <literal>foralls</literal>, e.g. +<screen> +ghci> :t GHC.ST.runST +GHC.ST.runST :: (forall s. GHC.ST.ST s a) -> a +</screen> +</para></listitem> +<listitem><para>If any of the quantified type variables has a kind +that mentions a kind variable, e.g. +<screen> +ghci> :i Data.Coerce.coerce +coerce :: + forall (k :: BOX) (a :: k) (b :: k). Coercible a b => a -> b + -- Defined in GHC.Prim +</screen> +</para></listitem> +</itemizedlist> + </para> + <para> + Using <option>-fprint-explicit-kinds</option> makes GHC print kind arguments in types, which are normally suppressed. This can be important when you are using kind polymorphism. For example: <screen> ghci> :set -XPolyKinds ghci> data T a = MkT ghci> :t MkT -MkT :: T b +MkT :: forall (k :: BOX) (a :: k). T a ghci> :set -fprint-explicit-foralls ghci> :t MkT -MkT :: forall (b::k). T b -ghci> :set -fprint-explicit-kinds -ghci> :t MkT -MkT :: forall (k::BOX) (b:k). T b +MkT :: forall (k :: BOX) (a :: k). T k a </screen> </para> </listitem> @@ -1719,15 +1736,50 @@ f "2" = 2 <indexterm><primary>unused binds, warning</primary></indexterm> <indexterm><primary>binds, unused</primary></indexterm> <para>Report any function definitions (and local bindings) - which are unused. For top-level functions, the warning is - only given if the binding is not exported.</para> - <para>A definition is regarded as "used" if (a) it is exported, or (b) it is - mentioned in the right hand side of another definition that is used, or (c) the - function it defines begins with an underscore. The last case provides a - way to suppress unused-binding warnings selectively. </para> - <para> Notice that a variable - is reported as unused even if it appears in the right-hand side of another - unused binding. </para> + which are unused. More precisely: + + <itemizedlist> + <listitem><para>Warn if a binding brings into scope a variable that is not used, + except if the variable's name starts with an underscore. The "starts-with-underscore" + condition provides a way to selectively disable the warning. + </para> + <para> + A variable is regarded as "used" if + <itemizedlist> + <listitem><para>It is exported, or</para></listitem> + <listitem><para>It appears in the right hand side of a binding that binds at + least one used variable that is used</para></listitem> + </itemizedlist> + For example + <programlisting> +module A (f) where +f = let (p,q) = rhs1 in t p -- Warning about unused q +t = rhs3 -- No warning: f is used, and hence so is t +g = h x -- Warning: g unused +h = rhs2 -- Warning: h is only used in the right-hand side of another unused binding +_w = True -- No warning: _w starts with an underscore + </programlisting> + </para></listitem> + + <listitem><para> + Warn if a pattern binding binds no variables at all, unless it is a lone, possibly-banged, wild-card pattern. + For example: + <programlisting> +Just _ = rhs3 -- Warning: unused pattern binding +(_, _) = rhs4 -- Warning: unused pattern binding +_ = rhs3 -- No warning: lone wild-card pattern +!_ = rhs4 -- No warning: banged wild-card pattern; behaves like seq + </programlisting> + The motivation for allowing lone wild-card patterns is they + are not very different from <literal>_v = rhs3</literal>, + which elicits no warning; and they can be useful to add a type + constraint, e.g. <literal>_ = x::Int</literal>. A lone + banged wild-card pattern is is useful as an alternative + (to <literal>seq</literal>) way to force evaluation. + </para> + </listitem> + </itemizedlist> + </para> </listitem> </varlistentry> @@ -1814,6 +1866,16 @@ f "2" = 2 </listitem> </varlistentry> + <varlistentry> + <term><option>-fwarn-inline-rule-shadowing</option>:</term> + <listitem> + <indexterm><primary><option>-fwarn-inline-rule-shadowing</option></primary></indexterm> + <para>Warn if a rewrite RULE might fail to fire because the function might be + inlined before the rule has a chance to fire. See <xref linkend="rules-inline"/>. + </para> + </listitem> + </varlistentry> + </variablelist> <para>If you're feeling really paranoid, the @@ -2967,44 +3029,6 @@ data D = D !C </sect1> &runtime; - -<sect1 id="ext-core"> - <title>Generating and compiling External Core Files</title> - - <indexterm><primary>intermediate code generation</primary></indexterm> - - <para>GHC can dump its optimized intermediate code (said to be in “Core” format) - to a file as a side-effect of compilation. Non-GHC back-end tools can read and process Core files; these files have the suffix - <filename>.hcr</filename>. The Core format is described in <ulink url="../../core.pdf"> - <citetitle>An External Representation for the GHC Core Language</citetitle></ulink>, - and sample tools - for manipulating Core files (in Haskell) are available in the - <ulink url="http://hackage.haskell.org/package/extcore">extcore package on Hackage</ulink>. Note that the format of <literal>.hcr</literal> - files is <emphasis>different</emphasis> from the Core output format that GHC generates - for debugging purposes (<xref linkend="options-debugging"/>), though the two formats appear somewhat similar.</para> - - <para>The Core format natively supports notes which you can add to - your source code using the <literal>CORE</literal> pragma (see <xref - linkend="pragmas"/>).</para> - - <variablelist> - - <varlistentry> - <term> - <option>-fext-core</option> - <indexterm><primary><option>-fext-core</option></primary></indexterm> - </term> - <listitem> - <para>Generate <literal>.hcr</literal> files.</para> - </listitem> - </varlistentry> - - </variablelist> - -<para>Currently (as of version 6.8.2), GHC does not have the ability to read in External Core files as source. If you would like GHC to have this ability, please <ulink url="http://ghc.haskell.org/trac/ghc/wiki/MailingListsAndIRC">make your wishes known to the GHC Team</ulink>.</para> - -</sect1> - &debug; &flags; |