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/* LIBGIMP - The GIMP Library
* Copyright (C) 1995-1997 Peter Mattis and Spencer Kimball
*
* Original file from libgimpwidgets: gimpeevl.h
* Copyright (C) 2008-2009 Fredrik Alstromer <roe@excu.se>
* Copyright (C) 2008-2009 Martin Nordholts <martinn@svn.gnome.org>
* Modified for Inkscape by Johan Engelen
* Copyright (C) 2011 Johan Engelen
*
* This library is free software: you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 3 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library. If not, see
* <http://www.gnu.org/licenses/>.
*/
#ifndef SEEN_GIMP_EEVL_H
#define SEEN_GIMP_EEVL_H
#include "util/units.h"
#include <exception>
#include <sstream>
#include <string>
/**
* @file
* Introducing eevl eva, the evaluator. A straightforward recursive
* descent parser, no fuss, no new dependencies. The lexer is hand
* coded, tedious, not extremely fast but works. It evaluates the
* expression as it goes along, and does not create a parse tree or
* anything, and will not optimize anything. It uses doubles for
* precision, with the given use case, that's enough to combat any
* rounding errors (as opposed to optimizing the evalutation).
*
* It relies on external unit resolving through a callback and does
* elementary dimensionality constraint check (e.g. "2 mm + 3 px * 4
* in" is an error, as L + L^2 is a missmatch). It uses g_strtod() for numeric
* conversions and it's non-destructive in terms of the paramters, and
* it's reentrant.
*
* EBNF:
*
* expression ::= term { ('+' | '-') term }* |
* <empty string> ;
*
* term ::= signed factor { ( '*' | '/' ) signed factor }* ;
*
* signed factor ::= ( '+' | '-' )? factor ;
*
* unit factor ::= factor unit? ;
*
* factor ::= number | '(' expression ')' ;
*
* number ::= ? what g_strtod() consumes ? ;
*
* unit ::= ? what not g_strtod() consumes and not whitespace ? ;
*
* The code should match the EBNF rather closely (except for the
* non-terminal unit factor, which is inlined into factor) for
* maintainability reasons.
*
* It will allow 1++1 and 1+-1 (resulting in 2 and 0, respectively),
* but I figured one might want that, and I don't think it's going to
* throw anyone off.
*/
namespace Inkscape {
namespace Util {
class Unit;
/**
* GimpEevlQuantity:
* @value: In reference units.
* @dimension: in has a dimension of 1, in^2 has a dimension of 2 etc
*/
typedef struct
{
double value;
gint dimension;
} GimpEevlQuantity;
typedef bool (* GimpEevlUnitResolverProc) (const gchar *identifier,
GimpEevlQuantity *result,
Unit* unit);
GimpEevlQuantity gimp_eevl_evaluate (const gchar* string, Unit* unit = NULL);
/**
* Special exception class for the expression evaluator.
*/
class EvaluatorException : public std::exception {
public:
EvaluatorException(const char * message, const char *at_position) {
std::ostringstream os;
const char* token = at_position ? at_position : "<End of input>";
os << "Expression evaluator error: " << message << " at '" << token << "'";
msgstr = os.str();
}
virtual ~EvaluatorException() throw() {} // necessary to destroy the string object!!!
virtual const char* what() const throw () {
return msgstr.c_str();
}
protected:
std::string msgstr;
};
}
}
#endif // SEEN_GIMP_EEVL_H
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