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<chapter id="answers">
  <title>Answers to Exercises</title>

  <bridgehead>Exercise 3.1</bridgehead>

  <para>This is something of a trick question, for which I apologize.
    The trick comes from the &unix; definition of a suffix, which
    <application>PMake</application> does not necessarily share.
    You will have noticed that all the suffixes used in this tutorial
    (and in &unix; in general) begin with a period
    (<filename>.ms</filename>, <filename>.c</filename>, etc.).
    Now, <application>PMake</application>'s idea of a suffix is more
    like English's: it's the characters at the end of a word.  With
    this in mind, one possible solution to this problem goes as
    follows:</para>

  <programlisting>.SUFFIXES       : ec.exe .exe ec.obj .obj .asm
ec.objec.exe .obj.exe :
	link -o $(.TARGET) $(.IMPSRC)
.asmec.obj      :
	asm -o $(.TARGET) -DDO_ERROR_CHECKING $(.IMPSRC)
.asm.obj        :
	asm -o $(.TARGET) $(.IMPSRC)</programlisting>

  <bridgehead>Excercise 3.2</bridgehead>

  <para>The trick to this one lies in the <literal>:=</literal>
    variable-assignment operator and the <literal>:S</literal>
    variable-expansion modifier.  Basically what you want is to take
    the pointer variable, so to speak, and transform it into an
    invocation of the variable at which it points.  You might try
    something like:</para>

  <programlisting>$(PTR:S/^/\$(/:S/$/))</programlisting>

  <para>which places <literal>$(</literal> at the front of the
    variable name and <literal>)</literal> at the end, thus
    transforming <literal>VAR,</literal> for example, into
    <literal>$(VAR)</literal>, which is just what we want.
    Unfortunately (as you know if you have tried it), since, as it
    says in the hint, <application>PMake</application> does no further
    substitution on the result of a modified expansion, that is all
    you get.  The solution is to make use of <literal>:=</literal> to
    place that string into yet another variable, then invoke the other
    variable directly:</para>

  <programlisting>*PTR            := $(PTR:S/^/\$(/:S/$/)/)</programlisting>

  <para>You can then use <literal>$(*PTR)</literal> to your heart's
    content.</para>
</chapter>

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