<literal>left</literal>:</para>
<screen>
+[qsort.hs:2:15-46] *Main> :set -fprint-evld-with-show
[qsort.hs:2:15-46] *Main> :print left
left = (_t1::[a])
</screen>
underscore, in this case
<literal>_t1</literal>.</para>
+ <para>The flag <literal>-fprint-evld-with-show</literal> instructs
+ <literal>:print</literal> to reuse
+ available <literal>Show</literal> instances when possible. This happens
+ only when the contents of the variable being inspected
+ are completely evaluated.</para>
+
+
<para>If we aren't concerned about preserving the evaluatedness of a
variable, we can use <literal>:force</literal> instead of
<literal>:print</literal>. The <literal>:force</literal> command
<para>The execution continued at the point it previously stopped, and has
now stopped at the breakpoint for a second time.</para>
+
<sect3 id="setting-breakpoints">
<title>Setting breakpoints</title>
bug. GHCi offers two variants of stepping. Use
<literal>:step</literal> to enable all the
breakpoints in the program, and execute until the next breakpoint is
- reached. Use <literal>:stepover</literal> to step over function
- applications, which of course are executed all the same.
+ reached. Use <literal>:steplocal</literal> to limit the set
+ of enabled breakpoints to those in the current top level function.
+ Similarly, use <literal>:stepmodule</literal> to single step only on
+ breakpoints contained in the current module.
For example:</para>
<screen>
<literal>:trace</literal> and <literal>:history</literal> to establish
the context. However, <literal>head</literal> is in a library and
we can't set a breakpoint on it directly. For this reason, GHCi
- provides the flag <literal>-fbreak-on-exception</literal> which causes
- the evaluator to stop when an exception is thrown, just as it does when
- a breakpoint is hit. This is only really useful in conjunction with
+ provides the flags <literal>-fbreak-on-exception</literal> which causes
+ the evaluator to stop when an exception is thrown, and <literal>
+ -fbreak-on-error</literal>, which works similarly but stops only on
+ uncaught exceptions. When stopping at an exception, GHCi will act
+ just as it does when a breakpoint is hit, with the deviation that it
+ will not show you any source code location. Due to this, these
+ commands are only really useful in conjunction with
<literal>:trace</literal>, in order to log the steps leading up to the
exception. For example:</para>