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authorAdrian Kummerlaender2015-03-03 20:12:32 +0100
committerAdrian Kummerlaender2015-03-03 20:12:32 +0100
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Added bindings section to latest article draft
Diffstat (limited to 'articles')
-rw-r--r--articles/2015-02-27_using_scheme_as_a_metaphor_for_template_metaprogramming.md41
1 files changed, 40 insertions, 1 deletions
diff --git a/articles/2015-02-27_using_scheme_as_a_metaphor_for_template_metaprogramming.md b/articles/2015-02-27_using_scheme_as_a_metaphor_for_template_metaprogramming.md
index 4ab74ee..3781645 100644
--- a/articles/2015-02-27_using_scheme_as_a_metaphor_for_template_metaprogramming.md
+++ b/articles/2015-02-27_using_scheme_as_a_metaphor_for_template_metaprogramming.md
@@ -133,7 +133,46 @@ using Fold = Eval<detail::fold_pair<Function, Initial, List>>;
Hiding member type defintions behind template aliases enables most _higher_ functionality and applications built using it's functions to be written in a reasonably minimalistic - _Scheme_ like - fashion as we can see in e.g. the listing of `Every`. This also explains why `tav::Pair` recursively defines it's own type, as we would otherwise have to be quite careful where to resolve `tav::Eval`.
-## Partial function application
+### Bindings
+
+Not all programs are sensibly expressed as a nested chain of function calls if we want to reuse some values, separate functionality into appropriately named functions and hide complexity via private bindings. While in _Scheme_ one would use `let` and the like for this purpose, such functionality is not easily replicated in the context of template metaprogramming. This is why _TypeAsValue_ uses a alternate and more _C++ like_ solution to this problem by simply making use of the standard object oriented aspects of the language.
+
+~~~
+template <
+ template<typename, typename> class Comparator,
+ typename Sequence
+>
+class quick_sort {
+ private:
+ using index = Divide<Length<Sequence>, Size<2>>;
+ using pivot = Nth<index, Sequence>;
+
+ using partitions = Partition<
+ Apply<Comparator, pivot, _0>::template function,
+ DeleteNth<index, Sequence>
+ >;
+
+ using lhs = Car<partitions>;
+ using rhs = Cdr<partitions>;
+
+ public:
+ using type = Concatenate<
+ Eval<quick_sort<Comparator, lhs>>,
+ List<pivot>,
+ Eval<quick_sort<Comparator, rhs>>
+ >;
+};
+
+template <template<typename, typename> class Comparator>
+struct quick_sort<Comparator, void> {
+ typedef void type;
+};
+~~~
+{:.language-cpp}
+
+Above we can see the complete listing of the _Quick Sort_ implementation employed by the `tav::Sort` template alias. At first glance this looks rather different from a _Scheme_ program but if we look closer on could argue that it is a equivalent of a `let` binding where the _private_ section of `tav::detail::quick_sort` contains the bound constants and the _public_ section contains the body.
+
+### Partial function application
## Examples