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Correct example and documentation.

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This commit is contained in:
Kohei Takahashi
2017-06-28 22:58:18 +09:00
parent 7ed1700ac3
commit 8a2eb9da25
2 changed files with 36 additions and 20 deletions
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doc/examples/transforming.qbk
+23 -12
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@@ -25,21 +25,36 @@ multiplication.
Let's start with defining our default action:
[def __proto_nary_expr__ [@http://www.boost.org/doc/libs/release/doc/html/boost/proto/nary_expr.html `proto::nary_expr`]]
[def __proto_vararg__ [@http://www.boost.org/doc/libs/release/doc/html/boost/proto/vararg.html `proto::vararg`]]
[def __proto_when__ [@http://www.boost.org/doc/libs/release/doc/html/boost/proto/when.html `proto::when`]]
[def __proto_underscore__ [@http://www.boost.org/doc/libs/release/doc/html/boost/proto/_.html `proto::_`]]
[def __proto_make_expr__ [@http://www.boost.org/doc/libs/release/doc/html/boost/proto/functional/make_expr.html `proto::functional::make_expr`]]
struct invert_actions
{
template <typename Rule>
struct when
: proto::_ // the default is proto::_
: __proto_nary_expr__
__proto_underscore__
, __proto_vararg__
__proto_when__<__proto_underscore__, phoenix::evaluator(__proto_underscore__, phoenix::_context)
>
>
{};
};
By default, we don't want to do anything, well, not exactly nothing, but just
return the expression. This is done by
[@http://www.boost.org/doc/libs/release/doc/html/boost/proto/_.html proto::_]
which, used as a transform, just passes the current expression along. Making this
action an identity transform.
Wow, this looks complicated! Granted you need to know a little bit about __proto__
(For a good introduction read through the
[@http://cpp-next.com/archive/2010/08/expressive-c-introduction/ Expressive C++] series).
[def __proto_make_expr__ [@http://www.boost.org/doc/libs/release/doc/html/boost/proto/functional/make_expr.html `proto::functional::make_expr`]]
By default, we don't want to do anything, well, not exactly nothing, but just
continue transformation into its arguments.
So, it is done by the following:
* For each arguments are passed to evaluator (with the current context, that contains our invert_actions)
* Create new expression using current expression tag, what is done by __proto_underscore__, with the result of evaluated arguments
So, after the basics are set up, we can start by writing the transformations we
want to have on our tree:
@@ -55,15 +70,11 @@ want to have on our tree:
>
{};
Wow, this looks complicated! Granted you need to know a little bit about __proto__
(For a good introduction read through the
[@http://cpp-next.com/archive/2010/08/expressive-c-introduction/ Expressive C++] series).
What is done is the following:
* The left expression is passed to evaluator (with the current context, that contains our invert_actions)
* The right expression is passed to evaluator (with the current context, that contains our invert_actions)
* The result of these two __proto_transforms__ is passed to __proto_make_expr__ which returns the freshly created expression
* The result of these two __proto_transforms__ are passed to __proto_make_expr__ which returns the freshly created expression
After you know what is going on, maybe the rest doesn't look so scary anymore:
example/invert.cpp
+13 -8
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@@ -13,14 +13,6 @@
namespace phoenix = boost::phoenix;
namespace proto = boost::proto;
struct invert_actions
{
template <typename Rule>
struct when
: proto::_
{};
};
using phoenix::evaluator;
#ifdef _MSC_VER
@@ -29,6 +21,19 @@ using phoenix::evaluator;
#define evaluator(A0, A1) proto::call<phoenix::evaluator(A0, A1)>
#endif
struct invert_actions
{
template <typename Rule>
struct when
: proto::nary_expr<
proto::_
, proto::vararg<
proto::when<proto::_, evaluator(proto::_, phoenix::_context)>
>
>
{};
};
template <>
struct invert_actions::when<phoenix::rule::plus>
: proto::call<