conditional.h

#ifndef LIBWCCL_OPS_FUNCTIONS_CONDITIONAL_H
#define LIBWCCL_OPS_FUNCTIONS_CONDITIONAL_H

#include <boost/format.hpp>
#include <libwccl/ops/functions/constant.h>

namespace Wccl {

/**
 * Template class for conditional operators, returning value
 * depending on evaluation of some predicate.
 * This class is targeted towards if..then..else expression
 */
template<class T>
class Conditional : public Function<T>
{
public:
	typedef boost::shared_ptr<const Function<T> > ArgFunctionPtr;
	typedef boost::shared_ptr<const Function<Bool> > BoolFunctionPtr;
	
	Conditional(
		const BoolFunctionPtr& cond_expr,
		const ArgFunctionPtr& iftrue_expr,
		const ArgFunctionPtr& iffalse_expr = Default())
		: cond_expr_(cond_expr), iftrue_expr_(iftrue_expr), iffalse_expr_(iffalse_expr)
	{
		BOOST_ASSERT(cond_expr_);
		BOOST_ASSERT(iftrue_expr_);
		BOOST_ASSERT(iffalse_expr_);
	}

	/**
	 * String representation of conditional operator in form of:
	 * "if(cond_expr_string, iftrue_expr_string, iffalse_expr_string)"
	 */
	std::string to_string(const Corpus2::Tagset& tagset) const;

	/**
	 * @returns Name of the function: "if"
	 */
	std::string raw_name() const {
		return "if";
	}

protected:
	const BoolFunctionPtr cond_expr_;
	const ArgFunctionPtr iftrue_expr_;
	const ArgFunctionPtr iffalse_expr_;

	/**
	 * Evaluate the predicate. If it is true, evaluate and return value of
	 * iftrue_expression. If predicate is false, evalute and return value
	 * of iffalse_expression.
	 */
	FunctionBase::BaseRetValPtr apply_internal(const FunExecContext& context) const;

	/**
	 * Writes raw string representation of conditional operator in form of:
	 * "if(cond_expr_raw_s, iftrue_expr_raw_s, iffalse_expr_raw_s)"
	 * This version does not require tagset, but may be inclomplete
	 * and/or contain internal info.
	 * @returns Stream written to.
	 */
	virtual std::ostream& write_to(std::ostream& ostream) const;

private:
	static const ArgFunctionPtr Default() {
		return detail::DefaultFunction<T>();
	}
};