<literal>:continue</literal>
<indexterm><primary><literal>:continue</literal></primary></indexterm>
</term>
- <listitem> Shortcut to <literal>:breakpoint continue </literal>
+ <listitem><para>Shortcut to <literal>:breakpoint continue</literal></para>
</listitem>
</varlistentry>
qsort2.hs:2:15-46>
</programlisting>
What is happening here is that GHCi has interrupted the evaluation of
- <code>qsort</code> at the breakpoint set in line 2, as the prompt indicates.
+ <literal>qsort</literal> at the breakpoint set in line 2, as the prompt indicates.
At this point you can freely explore the contents of the bindings in scope,
but with two catches. </para><para>
First, take into account that due to the lazy nature of Haskell, some of
trigger a computation. </para><para>
Second: look at the types of the things in scope.
GHCi has left its types parameterised by a variable!
- Look at the type of <code>qsort</code>, which is
+ Look at the type of <literal>qsort</literal>, which is
polymorphic on the type of its argument. It does not
- tell us really what the types of <code>x</code> and <code>xs</code> can be.
+ tell us really what the types of <literal>x</literal> and <literal>xs</literal> can be.
In general, polymorphic programs deal with polymorphic values,
and this means that some of the bindings available in a breakpoint site
will be parametrically typed.
This is useful because you cannot just type <literal>x</literal> in the
prompt and expect GHCi to return you its value. Perhaps you know for
sure that
- <literal>x</literal> is of type <code>Int</code>, which is an instance of
- <code>Show</code>, but GHCi does not have this information.
- <code>:print</code> however is fine, because it does not need to know the
+ <literal>x</literal> is of type <literal>Int</literal>, which is an instance of
+ <literal>Show</literal>, but GHCi does not have this information.
+ <literal>:print</literal> however is fine, because it does not need to know the
type to do its work. </para>
- <para> Let's go on with the debugging session of the <code>qsort</code>
+ <para> Let's go on with the debugging session of the <literal>qsort</literal>
example:
<example id="debuggingEx"><title>A short debugging session</title>
<programlisting>
<para>GHCi reminds us that this value is untyped, and instructs us to force its evaluation </para>
</callout>
<callout arearefs="seq2">
- <para>This line forces the evaluation of <code>x</code> </para>
+ <para>This line forces the evaluation of <literal>x</literal> </para>
</callout>
<callout arearefs="seq3">
<para>Even though x has been evaluated, we cannot simply use its name to see its value!
This is a bit counterintuitive, but currently in GHCi the type of a binding
- cannot be a type variable <code>a</code>.
- Thus, the binding <code>x</code> gets assigned the concrete type Unknown.</para>
+ cannot be a type variable <literal>a</literal>.
+ Thus, the binding <literal>x</literal> gets assigned the concrete type Unknown.</para>
</callout>
<callout arearefs="seq4">
- <para>We can explore <code>x</code> using the <literal>:print</literal>
- command, which does find out that <code>x</code> is of type Int and prints
+ <para>We can explore <literal>x</literal> using the <literal>:print</literal>
+ command, which does find out that <literal>x</literal> is of type Int and prints
its value accordingly.</para>
</callout>
<callout arearefs="seq5">
- <literal>:print</literal> also updates the type of <code>x</code> with
- the most concrete type information available.
+ <para><literal>:print</literal> also updates the type of <literal>x</literal> with
+ the most concrete type information available.</para>
</callout>
</calloutlist>
The example shows the standard way to proceeed with polymorphic values in a breakpoint.
<para>
<itemizedlist>
<listitem><para>
- <xref linkend="implicit-parameters" xrefstyle="select: title"/> are only available
+ Implicit parameters (see <xref linkend="implicit-parameters"/>) are only available
at the scope of a breakpoint if there is a explicit type signature.
</para></listitem>
</itemizedlist>
<programlisting>{-# OPTIONS_GHC -fdebugging #-}</programlisting>
</listitem>
</varlistentry>
- <varlistentry> <term>* Repeated use of <code>seq</code> and
+ <varlistentry> <term>* Repeated use of <literal>seq</literal> and
<literal>:print</literal> may be necessary to observe unevaluated
untyped bindings</term>
<listitem><para>see <xref linkend="debuggingEx"/>
</para></listitem>
</varlistentry>
- <varlistentry> <term> * <code>GHC.Exts.unsafeCoerce</code> can help if you are positive about the type of a binding</term>
+ <varlistentry> <term> * <literal>GHC.Exts.unsafeCoerce</literal> can help if you are positive about the type of a binding</term>
<listitem><para><programlisting>
type MyLongType a = [Maybe [Maybe a]]
<varlistentry> <term> * The undocumented (and unsupported) :force command </term>
<listitem><para>
equivalent to <literal> :print</literal> with automatic
- <code>seq</code> forcing,
- may prove useful to replace sequences of <code>seq</code> and
+ <literal>seq</literal> forcing,
+ may prove useful to replace sequences of <literal>seq</literal> and
<literal>:print</literal> in some situations.
</para></listitem>
</varlistentry>
<term>I can't use Control-C to interrupt computations in
GHCi on Windows.</term>
<listitem>
- <para>See <xref linkend="ghci-windows">.</xref></para>
+ <para>See <xref linkend="ghci-windows"/></para>
</listitem>
</varlistentry>
</variablelist>
projects / ghc-hetmet.git / blobdiff