<term><option>-fth</option></term>
<listitem>
<para>Enables Template Haskell (see <xref
- linkend="template-haskell"/>). Currently also implied by
+ linkend="template-haskell"/>). This flag must
+ be given explicitly; it is no longer implied by
<option>-fglasgow-exts</option>.</para>
<para>Syntax stolen: <literal>[|</literal>,
declaration (after expansion of any type synonyms)
<programlisting>
- newtype T v1...vn = T' (S t1...tk vk+1...vn) deriving (c1...cm)
+ newtype T v1...vn = T' (t vk+1...vn) deriving (c1...cm)
</programlisting>
where
<itemizedlist>
<listitem><para>
- <literal>S</literal> is a type constructor,
+ The type <literal>t</literal> is an arbitrary type
</para></listitem>
<listitem><para>
- The <literal>t1...tk</literal> are types,
-</para></listitem>
-<listitem><para>
- The <literal>vk+1...vn</literal> are type variables which do not occur in any of
- the <literal>ti</literal>, and
+ The <literal>vk+1...vn</literal> are type variables which do not occur in
+ <literal>t</literal>, and
</para></listitem>
<listitem><para>
The <literal>ci</literal> are partial applications of
Then, for each <literal>ci</literal>, the derived instance
declaration is:
<programlisting>
- instance ci (S t1...tk vk+1...v) => ci (T v1...vp)
+ instance ci (t vk+1...v) => ci (T v1...vp)
</programlisting>
where <literal>p</literal> is chosen so that <literal>T v1...vp</literal> is of the
right <emphasis>kind</emphasis> for the last parameter of class <literal>Ci</literal>.
constructions. You need to use the flag
<option>-fth</option><indexterm><primary><option>-fth</option></primary>
</indexterm>to switch these syntactic extensions on
- (<option>-fth</option> is currently implied by
- <option>-fglasgow-exts</option>, but you are encouraged to
- specify it explicitly).</para>
+ (<option>-fth</option> is no longer implied by
+ <option>-fglasgow-exts</option>).</para>
<itemizedlist>
<listitem><para>
If you use <option>-dverbose-core2core</option> you'll see the
sequence of phase numbers for successive runs of the
simplifier. In an INLINE pragma you can optionally specify a
- phase number, thus:</para>
-
+ phase number, thus:
<itemizedlist>
<listitem>
- <para>You can say "inline <literal>f</literal> in Phase 2
- and all subsequent phases":
-<programlisting>
- {-# INLINE [2] f #-}
-</programlisting>
- </para>
- </listitem>
-
+ <para>"<literal>INLINE[k] f</literal>" means: do not inline
+ <literal>f</literal>
+ until phase <literal>k</literal>, but from phase
+ <literal>k</literal> onwards be very keen to inline it.
+ </para></listitem>
<listitem>
- <para>You can say "inline <literal>g</literal> in all
- phases up to, but not including, Phase 3":
-<programlisting>
- {-# INLINE [~3] g #-}
-</programlisting>
- </para>
- </listitem>
-
+ <para>"<literal>INLINE[~k] f</literal>" means: be very keen to inline
+ <literal>f</literal>
+ until phase <literal>k</literal>, but from phase
+ <literal>k</literal> onwards do not inline it.
+ </para></listitem>
<listitem>
- <para>If you omit the phase indicator, you mean "inline in
- all phases".</para>
- </listitem>
+ <para>"<literal>NOINLINE[k] f</literal>" means: do not inline
+ <literal>f</literal>
+ until phase <literal>k</literal>, but from phase
+ <literal>k</literal> onwards be willing to inline it (as if
+ there was no pragma).
+ </para></listitem>
+ <listitem>
+ <para>"<literal>INLINE[~k] f</literal>" means: be willing to inline
+ <literal>f</literal>
+ until phase <literal>k</literal>, but from phase
+ <literal>k</literal> onwards do not inline it.
+ </para></listitem>
</itemizedlist>
-
- <para>You can use a phase number on a NOINLINE pragma too:</para>
-
- <itemizedlist>
- <listitem>
- <para>You can say "do not inline <literal>f</literal>
- until Phase 2; in Phase 2 and subsequently behave as if
- there was no pragma at all":
+The same information is summarised here:
<programlisting>
- {-# NOINLINE [2] f #-}
-</programlisting>
- </para>
- </listitem>
+ -- Before phase 2 Phase 2 and later
+ {-# INLINE [2] f #-} -- No Yes
+ {-# INLINE [~2] f #-} -- Yes No
+ {-# NOINLINE [2] f #-} -- No Maybe
+ {-# NOINLINE [~2] f #-} -- Maybe No
- <listitem>
- <para>You can say "do not inline <literal>g</literal> in
- Phase 3 or any subsequent phase; before that, behave as if
- there was no pragma":
-<programlisting>
- {-# NOINLINE [~3] g #-}
+ {-# INLINE f #-} -- Yes Yes
+ {-# NOINLINE f #-} -- No No
</programlisting>
- </para>
- </listitem>
-
- <listitem>
- <para>If you omit the phase indicator, you mean "never
- inline this function".</para>
- </listitem>
- </itemizedlist>
-
- <para>The same phase-numbering control is available for RULES
+By "Maybe" we mean that the usual heuristic inlining rules apply (if the
+function body is small, or it is applied to interesting-looking arguments etc).
+Another way to understand the semantics is this:
+<itemizedlist>
+<listitem><para>For both INLINE and NOINLINE, the phase number says
+when inlining is allowed at all.</para></listitem>
+<listitem><para>The INLINE pragma has the additional effect of making the
+function body look small, so that when inlining is allowed it is very likely to
+happen.
+</para></listitem>
+</itemizedlist>
+</para>
+<para>The same phase-numbering control is available for RULES
(<xref linkend="rewrite-rules"/>).</para>
</sect3>
</sect2>
projects / ghc-hetmet.git / blobdiff