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Glasgow Haskell Compiler
GHC
Commits
77a4675a
Commit
77a4675a
authored
Jun 05, 2009
by
Ian Lynagh
Browse files
Update the docs on how you bind unlifted types in let/where clauses
parent
8bf9fcc6
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docs/users_guide/glasgow_exts.xml
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77a4675a
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@@ -210,22 +210,20 @@ in a <emphasis>top-level</emphasis> binding.
in a
<emphasis>
recursive
</emphasis>
binding.
</para></listitem>
<listitem><para>
You may bind unboxed variables in a (non-recursive,
non-top-level) pattern binding, but any such variable causes the entire
pattern-match
to become strict. For example:
non-top-level) pattern binding, but you must make any such pattern-match
strict. For example, rather than:
<programlisting>
data Foo = Foo Int Int#
f x = let (Foo a b, w) = ..rhs.. in ..body..
</programlisting>
Since
<literal>
b
</literal>
has type
<literal>
Int#
</literal>
, the entire pattern
match
is strict, and the program behaves as if you had written
you must write:
<programlisting>
data Foo = Foo Int Int#
f x =
case ..rhs.. of {
(Foo a b, w)
->
..body..
}
f x =
let !
(Foo a b, w)
= ..rhs.. in
..body..
</programlisting>
since
<literal>
b
</literal>
has type
<literal>
Int#
</literal>
.
</para>
</listitem>
</itemizedlist>
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