Ichthyostega
75dd4210f2
...since the Policy class now defines the function signature, we can no longer assume that "input" is size_t. Rather, all invocations must rely on the generic adaptaion scheme. Getting this correct turns out rather tricky again; best to rely on a generic function-composition. Indeed I programmed such a helper several years ago, with the caveat that at that time we used C++03 and could not perfect-forward arguments. Today this problem can be solved much more succinct using generic Lambdas.
852 lines
29 KiB
C++
852 lines
29 KiB
C++
/*
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FUNCTION-CLOSURE.hpp - metaprogramming tools for closing a function over given arguments
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Copyright (C) Lumiera.org
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2009, Hermann Vosseler <Ichthyostega@web.de>
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This program is free software; you can redistribute it and/or
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modify it under the terms of the GNU General Public License as
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published by the Free Software Foundation; either version 2 of
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the License, or (at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program; if not, write to the Free Software
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Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
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*/
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/** @file function-closure.hpp
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** Partial function application and building a complete function closure.
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** This is a addendum to (and thin wrapper for) `<functional>`, supporting
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** the case when a function should be _closed_ over (partially or all) arguments,
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** where especially the parameter values to close on are provided as a tuple.
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** Additionally, we allow for composing (chaining) of two functions.
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**
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** Because we have to deal with arbitrary functions and arbitrary parameter types,
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** we need a lot of repetitive code to "catch" functions from zero to nine arguments.
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** At the bottom of this header, you'll find a function-style interface, which
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** wraps up all these technicalities.
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**
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** @todo the implementation is able to handle partial application with N arguments,
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** but currently we need just one argument, thus only this case was wrapped
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** up into a convenient functions func::applyFirst and func::applyLast
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**
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** @see control::CommandDef usage example
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** @see function.hpp
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**
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*/
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#ifndef LIB_META_FUNCTION_CLOSURE_H
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#define LIB_META_FUNCTION_CLOSURE_H
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#include "lib/meta/function.hpp"
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#include "lib/meta/tuple-helper.hpp"
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#include <functional>
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#include <tuple>
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namespace lib {
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namespace meta{
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namespace func{
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using std::function;
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using std::tuple;
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namespace { // helpers for binding and applying a function to an argument tuple
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using std::get;
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/**
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* this Helper with repetitive specialisations for up to nine arguments
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* is used either to apply a function to arguments given as a tuple, or
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* to create the actual closure (functor) over all function arguments.
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*/
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template<uint n>
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struct Apply;
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template<> //__________________________________
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struct Apply<0> ///< Apply function without Arguments
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{
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template<typename RET, class FUN, class TUP>
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static RET
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invoke (FUN& f, TUP&)
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{
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return f ();
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}
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template<typename RET, class FUN, class TUP>
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static RET
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bind (FUN& f, TUP&)
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{
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return std::bind (f);
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}
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};
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template<> //_________________________________
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struct Apply<1> ///< Apply function with 1 Argument
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{
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template<typename RET, class FUN, class TUP>
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static RET
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invoke (FUN& f, TUP & arg)
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{
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return f (get<0>(arg));
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}
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template<typename RET, class FUN, class TUP>
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static RET
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bind (FUN& f, TUP & arg)
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{
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return std::bind (f, get<0>(arg));
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}
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};
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template<> //_________________________________
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struct Apply<2> ///< Apply function with 2 Arguments
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{
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template<typename RET, class FUN, class TUP>
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static RET
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invoke (FUN& f, TUP & arg)
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{
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return f ( get<0>(arg)
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, get<1>(arg)
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);
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}
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template<typename RET, class FUN, class TUP>
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static RET
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bind (FUN& f, TUP & arg)
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{
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return std::bind (f, get<0>(arg)
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, get<1>(arg)
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);
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}
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};
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template<> //_________________________________
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struct Apply<3> ///< Apply function with 3 Arguments
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{
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template<typename RET, class FUN, class TUP>
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static RET
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invoke (FUN& f, TUP & arg)
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{
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return f ( get<0>(arg)
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, get<1>(arg)
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, get<2>(arg)
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);
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}
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template<typename RET, class FUN, class TUP>
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static RET
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bind (FUN& f, TUP & arg)
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{
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return std::bind (f, get<0>(arg)
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, get<1>(arg)
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, get<2>(arg)
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);
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}
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};
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template<> //_________________________________
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struct Apply<4> ///< Apply function with 4 Arguments
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{
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template<typename RET, class FUN, class TUP>
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static RET
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invoke (FUN& f, TUP & arg)
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{
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return f ( get<0>(arg)
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, get<1>(arg)
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, get<2>(arg)
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, get<3>(arg)
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);
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}
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template<typename RET, class FUN, class TUP>
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static RET
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bind (FUN& f, TUP & arg)
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{
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return std::bind (f, get<0>(arg)
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, get<1>(arg)
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, get<2>(arg)
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, get<3>(arg)
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);
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}
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};
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template<> //_________________________________
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struct Apply<5> ///< Apply function with 5 Arguments
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{
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template<typename RET, class FUN, class TUP>
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static RET
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invoke (FUN& f, TUP & arg)
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{
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return f ( get<0>(arg)
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, get<1>(arg)
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, get<2>(arg)
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, get<3>(arg)
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, get<4>(arg)
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);
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}
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template<typename RET, class FUN, class TUP>
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static RET
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bind (FUN& f, TUP & arg)
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{
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return std::bind (f, get<0>(arg)
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, get<1>(arg)
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, get<2>(arg)
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, get<3>(arg)
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, get<4>(arg)
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);
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}
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};
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template<> //_________________________________
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struct Apply<6> ///< Apply function with 6 Arguments
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{
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template<typename RET, class FUN, class TUP>
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static RET
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invoke (FUN& f, TUP & arg)
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{
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return f ( get<0>(arg)
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, get<1>(arg)
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, get<2>(arg)
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, get<3>(arg)
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, get<4>(arg)
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, get<5>(arg)
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);
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}
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template<typename RET, class FUN, class TUP>
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static RET
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bind (FUN& f, TUP & arg)
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{
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return std::bind (f, get<0>(arg)
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, get<1>(arg)
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, get<2>(arg)
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, get<3>(arg)
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, get<4>(arg)
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, get<5>(arg)
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);
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}
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};
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template<> //_________________________________
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struct Apply<7> ///< Apply function with 7 Arguments
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{
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template<typename RET, class FUN, class TUP>
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static RET
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invoke (FUN& f, TUP & arg)
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{
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return f ( get<0>(arg)
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, get<1>(arg)
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, get<2>(arg)
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, get<3>(arg)
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, get<4>(arg)
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, get<5>(arg)
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, get<6>(arg)
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);
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}
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template<typename RET, class FUN, class TUP>
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static RET
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bind (FUN& f, TUP & arg)
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{
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return std::bind (f, get<0>(arg)
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, get<1>(arg)
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, get<2>(arg)
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, get<3>(arg)
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, get<4>(arg)
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, get<5>(arg)
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, get<6>(arg)
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);
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}
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};
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template<> //_________________________________
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struct Apply<8> ///< Apply function with 8 Arguments
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{
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template<typename RET, class FUN, class TUP>
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static RET
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invoke (FUN& f, TUP & arg)
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{
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return f ( get<0>(arg)
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, get<1>(arg)
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, get<2>(arg)
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, get<3>(arg)
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, get<4>(arg)
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, get<5>(arg)
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, get<6>(arg)
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, get<7>(arg)
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);
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}
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template<typename RET, class FUN, class TUP>
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static RET
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bind (FUN& f, TUP & arg)
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{
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return std::bind (f, get<0>(arg)
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, get<1>(arg)
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, get<2>(arg)
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, get<3>(arg)
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, get<4>(arg)
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, get<5>(arg)
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, get<6>(arg)
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, get<7>(arg)
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);
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}
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};
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template<> //_________________________________
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struct Apply<9> ///< Apply function with 9 Arguments
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{
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template<typename RET, class FUN, class TUP>
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static RET
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invoke (FUN& f, TUP & arg)
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{
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return f ( get<0>(arg)
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, get<1>(arg)
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, get<2>(arg)
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, get<3>(arg)
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, get<4>(arg)
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, get<5>(arg)
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, get<6>(arg)
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, get<7>(arg)
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, get<8>(arg)
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);
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}
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template<typename RET, class FUN, class TUP>
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static RET
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bind (FUN& f, TUP & arg)
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{
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return std::bind (f, get<0>(arg)
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, get<1>(arg)
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, get<2>(arg)
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, get<3>(arg)
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, get<4>(arg)
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, get<5>(arg)
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, get<6>(arg)
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, get<7>(arg)
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, get<8>(arg)
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);
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}
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};
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/* ===== Helpers for partial function application ===== */
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/** @note relying on the implementation type
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* since we need to _build_ placeholders */
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using std::_Placeholder;
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/**
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* Build a list of standard function argument placeholder types.
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* For each of the elements of the provided reference list,
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* a Placeholder is added, numbers counting up starting with 1 (!)
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*/
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template<typename TYPES, size_t i=1>
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struct PlaceholderTuple
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: PlaceholderTuple<typename TYPES::List>
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{ };
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template<typename X, typename TAIL, size_t i>
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struct PlaceholderTuple<Node<X,TAIL>, i>
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{
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using TailPlaceholders = typename PlaceholderTuple<TAIL,i+1>::List;
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using List = Node<_Placeholder<i>, TailPlaceholders>;
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};
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template<size_t i>
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struct PlaceholderTuple<NullType, i>
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{
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using List = NullType;
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};
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using std::tuple_element;
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using std::tuple_size;
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using std::get;
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/**
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* Builder for a tuple instance, where only some ctor parameters are supplied,
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* while the remaining arguments will be default constructed. The use case is
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* creating of a function binder, where some arguments shall be passed through
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* (and thus be stored in the resulting closure), while other arguments are just
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* marked as "Placeholder" with `std::_Placeholder<i>`.
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* These placeholder marker terms just need to be default constructed, and will
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* then be stored into the desired positions. Later on, when actually invoking
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* such a partially closed function, only the arguments marked with placeholders
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* need to be supplied, while the other arguments will use the values hereby
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* "baked" into the closure.
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* @tparam TAR full target tuple type. Some oft the elements within this tuple will
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* be default constructed, some will be initialised from the SRC tuple
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* @tparam SRC argument tuple type, for the values _actually to be initialised_ here.
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* @tparam start position within TYPES, at which the sequence of init-arguments starts;
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* all other positions will just be default initialised
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* @see lib::meta::TupleConstructor
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*/
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template<typename SRC, typename TAR, size_t start>
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struct PartiallyInitTuple
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{
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template<size_t i>
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using DestType = typename std::tuple_element<i, TAR>::type;
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/**
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* define those index positions in the target tuple,
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* where init arguments shall be used on construction.
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* All other arguments will just be default initialised.
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*/
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static constexpr bool
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useArg (size_t idx)
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{
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return (start <= idx)
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and (idx < start + std::tuple_size<SRC>());
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}
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template<size_t idx, bool doPick = PartiallyInitTuple::useArg(idx)>
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struct IndexMapper
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{
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SRC const& initArgs;
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operator DestType<idx>()
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{
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return std::get<idx-start> (initArgs);
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}
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};
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template<size_t idx>
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struct IndexMapper<idx, false>
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{
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SRC const& initArgs;
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operator DestType<idx>()
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{
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return DestType<idx>();
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}
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};
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};
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} // (END) impl-namespace
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/* ======= core operations: closures and partial application ========= */
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/**
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* Closure-creating template.
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* The instance is linked (reference) to a given concrete argument tuple.
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* A functor with a matching signature may then either be _closed_ over
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* this argument values, or even be invoked right away with theses arguments.
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* @warning we take functor objects _and parameters_ by reference
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*/
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template<typename SIG>
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class TupleApplicator
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{
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using Args = typename _Fun<SIG>::Args;
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using Ret = typename _Fun<SIG>::Ret;
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using BoundFunc = function<Ret()>;
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enum { ARG_CNT = count<typename Args::List>::value };
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/** storing a ref to the parameter tuple */
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Tuple<Args>& params_;
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public:
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TupleApplicator (Tuple<Args>& args)
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: params_(args)
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{ }
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BoundFunc bind (SIG& f) { return Apply<ARG_CNT>::template bind<BoundFunc> (f, params_); }
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BoundFunc bind (function<SIG> const& f) { return Apply<ARG_CNT>::template bind<BoundFunc> (f, params_); }
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Ret operator() (SIG& f) { return Apply<ARG_CNT>::template invoke<Ret> (f, params_); }
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Ret operator() (function<SIG>& f) { return Apply<ARG_CNT>::template invoke<Ret> (f, params_); }
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};
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/**
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* Closing a function over its arguments.
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* This is a small usage example or spin-off,
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* having almost the same effect than invoking `std::bind()`.
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* The notable difference is that the function arguments for
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* creating the closure are passed in as one tuple compound.
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*/
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template<typename SIG>
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class FunctionClosure
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{
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typedef typename _Fun<SIG>::Args Args;
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typedef typename _Fun<SIG>::Ret Ret;
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function<Ret(void)> closure_;
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public:
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FunctionClosure (SIG& f, Tuple<Args>& arg)
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: closure_(TupleApplicator<SIG>(arg).bind(f))
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{ }
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FunctionClosure (function<SIG> const& f, Tuple<Args>& arg)
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: closure_(TupleApplicator<SIG>(arg).bind(f))
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{ }
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Ret operator() () { return closure_(); }
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typedef Ret result_type; ///< for STL use
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typedef void argument_type;
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};
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|
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/**
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* Partial function application
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* Takes a function and a value tuple,
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* using the latter to close function arguments
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* either from the front (left) or aligned to the end
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* of the function argument list. Result is a "reduced" function,
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* expecting only the remaining "un-closed" arguments at invocation.
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* @tparam SIG signature of the function to be closed, either as
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* function reference type or `std::function` object
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* @tparam VAL type sequence describing the tuple of values
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* used for closing arguments
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* @note the construction of this helper template does not verify or
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* match types to the signature. In case of mismatch, you'll get
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* a compilation failure from `std::bind` (which can be confusing)
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*/
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template<typename SIG, typename VAL>
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class PApply
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{
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typedef typename _Fun<SIG>::Args Args;
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typedef typename _Fun<SIG>::Ret Ret;
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typedef typename Args::List ArgsList;
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typedef typename VAL::List ValList;
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typedef typename Types<ValList>::Seq ValTypes;
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enum { ARG_CNT = count<ArgsList>::value
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, VAL_CNT = count<ValList> ::value
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, ROFFSET = (VAL_CNT < ARG_CNT)? ARG_CNT-VAL_CNT : 0
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};
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// create list of the *remaining* arguments, after applying the ValList
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typedef typename Splice<ArgsList, ValList>::Back LeftReduced;
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typedef typename Splice<ArgsList, ValList, ROFFSET>::Front RightReduced;
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typedef typename Types<LeftReduced>::Seq ArgsL;
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typedef typename Types<RightReduced>::Seq ArgsR;
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// build a list, where each of the *remaining* arguments is replaced by a placeholder marker
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typedef typename func::PlaceholderTuple<LeftReduced>::List TrailingPlaceholders;
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typedef typename func::PlaceholderTuple<RightReduced>::List LeadingPlaceholders;
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// ... and splice these placeholders on top of the original argument type list,
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// thus retaining the types to be closed, but setting a placeholder for each remaining argument
|
||
typedef typename Splice<ArgsList, TrailingPlaceholders, VAL_CNT>::List LeftReplaced;
|
||
typedef typename Splice<ArgsList, LeadingPlaceholders, 0 >::List RightReplaced;
|
||
|
||
typedef typename Types<LeftReplaced>::Seq LeftReplacedTypes;
|
||
typedef typename Types<RightReplaced>::Seq RightReplacedTypes;
|
||
|
||
// create a "builder" helper, which accepts exactly the value tuple elements
|
||
// and puts them at the right location, while default-constructing the remaining
|
||
// (=placeholder)-arguments. Using this builder helper, we can finally set up
|
||
// the argument tuples (Left/RightReplacedArgs) used for the std::bind call
|
||
template<class SRC, class TAR, size_t i>
|
||
using IdxSelectorL = typename PartiallyInitTuple<SRC, TAR, 0>::template IndexMapper<i>;
|
||
|
||
template<class SRC, class TAR, size_t i>
|
||
using IdxSelectorR = typename PartiallyInitTuple<SRC, TAR, ROFFSET>::template IndexMapper<i>;
|
||
|
||
using BuildL = TupleConstructor<LeftReplacedTypes, IdxSelectorL>;
|
||
using BuildR = TupleConstructor<RightReplacedTypes, IdxSelectorR>;
|
||
|
||
|
||
/** Tuple to hold all argument values, starting from left.
|
||
* Any remaining positions behind the substitute values are occupied by binding placeholders */
|
||
using LeftReplacedArgs = Tuple<LeftReplacedTypes>;
|
||
|
||
/** Tuple to hold all argument values, aligned to the end of the function argument list.
|
||
* Any remaining positions before the substitute values are occupied by binding placeholders */
|
||
using RightReplacedArgs = Tuple<RightReplacedTypes>;
|
||
|
||
|
||
public:
|
||
typedef function<typename FunctionTypedef<Ret,ArgsL>::Sig> LeftReducedFunc;
|
||
typedef function<typename FunctionTypedef<Ret,ArgsR>::Sig> RightReducedFunc;
|
||
|
||
|
||
/** do a partial function application, closing the first arguments<br/>
|
||
* `f(a,b,c)->res + (a,b)` yields `f(c)->res`
|
||
*
|
||
* @param f function, function pointer or functor
|
||
* @param arg value tuple, used to close function arguments starting from left
|
||
* @return new function object, holding copies of the values and using them at the
|
||
* closed arguments; on invocation, only the remaining arguments need to be supplied.
|
||
*/
|
||
static LeftReducedFunc
|
||
bindFront (SIG const& f, Tuple<ValTypes> const& arg)
|
||
{
|
||
LeftReplacedArgs params {BuildL(arg)};
|
||
return func::Apply<ARG_CNT>::template bind<LeftReducedFunc> (f, params);
|
||
}
|
||
|
||
/** do a partial function application, closing the last arguments<br/>
|
||
* `f(a,b,c)->res + (b,c)` yields `f(a)->res`
|
||
*
|
||
* @param f function, function pointer or functor
|
||
* @param arg value tuple, used to close function arguments starting from right
|
||
* @return new function object, holding copies of the values and using them at the
|
||
* closed arguments; on invocation, only the remaining arguments need to be supplied.
|
||
*/
|
||
static RightReducedFunc
|
||
bindBack (SIG const& f, Tuple<ValTypes> const& arg)
|
||
{
|
||
RightReplacedArgs params {BuildR(arg)};
|
||
return func::Apply<ARG_CNT>::template bind<RightReducedFunc> (f, params);
|
||
}
|
||
};
|
||
|
||
|
||
|
||
/**
|
||
* Bind a specific argument to an arbitrary value.
|
||
* Especially, this "value" might be another binder.
|
||
*/
|
||
template<typename SIG, typename X, uint pos>
|
||
class BindToArgument
|
||
{
|
||
typedef typename _Fun<SIG>::Args Args;
|
||
typedef typename _Fun<SIG>::Ret Ret;
|
||
typedef typename Args::List ArgsList;
|
||
typedef typename Types<X>::List ValList;
|
||
|
||
enum { ARG_CNT = count<ArgsList>::value };
|
||
|
||
typedef typename Splice<ArgsList, ValList, pos>::Front RemainingFront;
|
||
typedef typename Splice<ArgsList, ValList, pos>::Back RemainingBack;
|
||
typedef typename func::PlaceholderTuple<RemainingFront>::List PlaceholdersBefore;
|
||
typedef typename func::PlaceholderTuple<RemainingBack,pos+1>::List PlaceholdersBehind;
|
||
typedef typename Append< typename Append< PlaceholdersBefore
|
||
, ValList >::List
|
||
, PlaceholdersBehind >::List PreparedArgs;
|
||
typedef typename Append<RemainingFront, RemainingBack>::List ReducedArgs;
|
||
|
||
using PreparedArgTypes = typename Types<PreparedArgs>::Seq;
|
||
using RemainingArgs = typename Types<ReducedArgs>::Seq;
|
||
|
||
using ReducedSig = typename FunctionTypedef<Ret,RemainingArgs>::Sig;
|
||
|
||
template<class SRC, class TAR, size_t i>
|
||
using IdxSelector = typename PartiallyInitTuple<SRC, TAR, pos>::template IndexMapper<i>;
|
||
|
||
using BuildPreparedArgs = TupleConstructor<PreparedArgTypes, IdxSelector>;
|
||
|
||
|
||
|
||
public:
|
||
typedef function<ReducedSig> ReducedFunc;
|
||
|
||
static ReducedFunc
|
||
reduced (SIG& f, Tuple<Types<X>> const& val)
|
||
{
|
||
Tuple<PreparedArgTypes> params {BuildPreparedArgs(val)};
|
||
return func::Apply<ARG_CNT>::template bind<ReducedFunc> (f, params);
|
||
}
|
||
};
|
||
|
||
|
||
|
||
namespace { // ...helpers for specifying types in function declarations....
|
||
|
||
template<typename RET, typename ARG>
|
||
struct _Sig
|
||
{
|
||
typedef typename FunctionTypedef<RET, ARG>::Sig Type;
|
||
typedef TupleApplicator<Type> Applicator;
|
||
};
|
||
|
||
template<typename SIG, typename ARG>
|
||
struct _Clo
|
||
{
|
||
typedef typename _Fun<SIG>::Ret Ret;
|
||
typedef typename _Sig<Ret,ARG>::Type Signature;
|
||
typedef FunctionClosure<Signature> Type;
|
||
};
|
||
|
||
template<typename FUN1, typename FUN2>
|
||
struct _Chain
|
||
{
|
||
typedef typename _Fun<FUN1>::Args Args;
|
||
typedef typename _Fun<FUN2>::Ret Ret;
|
||
typedef typename FunctionTypedef<Ret, Args>::Sig ChainedSig;
|
||
typedef function<ChainedSig> Functor;
|
||
};
|
||
|
||
template<typename SIG>
|
||
struct _PapS
|
||
{
|
||
typedef typename _Fun<SIG>::Ret Ret;
|
||
typedef typename _Fun<SIG>::Args Args;
|
||
typedef typename Split<Args>::Head Arg;
|
||
typedef typename Split<Args>::Tail Rest;
|
||
typedef typename _Sig<Ret,Rest>::Type Signature;
|
||
typedef function<Signature> Function;
|
||
};
|
||
|
||
template<typename SIG>
|
||
struct _PapE
|
||
{
|
||
typedef typename _Fun<SIG>::Ret Ret;
|
||
typedef typename _Fun<SIG>::Args Args;
|
||
typedef typename Split<Args>::End Arg;
|
||
typedef typename Split<Args>::Prefix Rest;
|
||
typedef typename _Sig<Ret,Rest>::Type Signature;
|
||
typedef function<Signature> Function;
|
||
};
|
||
|
||
} // (End) argument type shortcuts
|
||
|
||
|
||
|
||
|
||
/* ========== function-style interface ============= */
|
||
|
||
/** build a TupleApplicator, which embodies the given
|
||
* argument tuple and can be used to apply them
|
||
* to various functions repeatedly.
|
||
*/
|
||
template<typename...ARG>
|
||
inline
|
||
typename _Sig<void, Types<ARG...>>::Applicator
|
||
tupleApplicator (std::tuple<ARG...>& args)
|
||
{
|
||
typedef typename _Sig<void,Types<ARG...>>::Type Signature;
|
||
return TupleApplicator<Signature> (args);
|
||
}
|
||
|
||
|
||
/** apply the given function to the argument tuple */
|
||
template<typename SIG, typename...ARG>
|
||
inline
|
||
typename _Fun<SIG>::Ret
|
||
apply (SIG& f, std::tuple<ARG...>& args)
|
||
{
|
||
typedef typename _Fun<SIG>::Ret Ret; //
|
||
typedef typename _Sig<Ret,Types<ARG...>>::Type Signature; // Note: deliberately re-building the Signature Type
|
||
return TupleApplicator<Signature> (args) (f); // in order to get better error messages here
|
||
}
|
||
|
||
/** close the given function over all arguments,
|
||
* using the values from the argument tuple.
|
||
* @return a closure object, which can be
|
||
* invoked later to yield the
|
||
* function result. */
|
||
template<typename SIG, typename...ARG>
|
||
inline
|
||
typename _Clo<SIG,Types<ARG...>>::Type
|
||
closure (SIG& f, std::tuple<ARG...>& args)
|
||
{
|
||
typedef typename _Clo<SIG,Types<ARG...>>::Type Closure;
|
||
return Closure (f,args);
|
||
}
|
||
|
||
|
||
/** close the given function over the first argument */
|
||
template<typename SIG, typename ARG>
|
||
inline
|
||
typename _PapS<SIG>::Function
|
||
applyFirst (SIG& f, ARG arg)
|
||
{
|
||
typedef typename _PapS<SIG>::Arg ArgType;
|
||
typedef Types<ArgType> ArgTypeSeq;
|
||
typedef Tuple<ArgTypeSeq> ArgTuple;
|
||
ArgTuple val(arg);
|
||
return PApply<SIG,ArgTypeSeq>::bindFront (f, val);
|
||
}
|
||
|
||
/** close the given function over the last argument */
|
||
template<typename SIG, typename ARG>
|
||
inline
|
||
typename _PapE<SIG>::Function
|
||
applyLast (SIG& f, ARG arg)
|
||
{
|
||
typedef typename _PapE<SIG>::Arg ArgType;
|
||
typedef Types<ArgType> ArgTypeSeq;
|
||
typedef Tuple<ArgTypeSeq> ArgTuple;
|
||
ArgTuple val(arg);
|
||
return PApply<SIG,ArgTypeSeq>::bindBack (f, val);
|
||
}
|
||
|
||
|
||
/** bind the last function argument to an arbitrary term,
|
||
* which especially might be a (nested) binder... */
|
||
template<typename SIG, typename TERM>
|
||
inline
|
||
typename _PapE<SIG>::Function
|
||
bindLast (SIG& f, TERM const& arg)
|
||
{
|
||
typedef Types<TERM> ArgTypeSeq;
|
||
typedef Tuple<ArgTypeSeq> ArgTuple;
|
||
ArgTuple argT(arg);
|
||
enum { LAST_POS = -1 + count<typename _Fun<SIG>::Args::List>::value };
|
||
return BindToArgument<SIG,TERM,LAST_POS>::reduced (f, argT);
|
||
}
|
||
|
||
|
||
/** build a functor chaining the given functions: feed the result of f1 into f2.
|
||
* @note the mathematical notation would be `chained ≔ f2 ∘f1`
|
||
*/
|
||
template<typename FUN1, typename FUN2>
|
||
inline auto
|
||
chained (FUN1&& f1, FUN2&& f2)
|
||
{
|
||
using Ret = typename _Chain<FUN1,FUN2>::Ret;
|
||
|
||
return [functor1 = std::forward<FUN1> (f1)
|
||
,functor2 = std::forward<FUN2> (f2)]
|
||
(auto&& ...args) -> Ret
|
||
{
|
||
return functor2 (functor1 (std::forward<decltype(args)> (args)...));
|
||
};
|
||
}
|
||
|
||
|
||
|
||
}}} // namespace lib::meta::func
|
||
#endif
|