########################################################################
# $Header: /var/local/cvsroot/4Suite/Ft/Xml/XPath/ParsedExpr.py,v 1.47 2006/08/16 21:20:44 jkloth Exp $
"""
The implementation of parsed XPath expression tokens.

Copyright 2005 Fourthought, Inc. (USA).
Detailed license and copyright information: http://4suite.org/COPYRIGHT
Project home, documentation, distributions: http://4suite.org/
"""

import types, inspect
from xml.dom import Node

from Ft.Lib import boolean, number
from Ft.Lib.Set import Union, Unique
from Ft.Xml import EMPTY_NAMESPACE
from Ft.Xml.Lib.XmlString import SplitQName, XmlStrStrip
from Ft.Xml.XPath import RuntimeException
from Ft.Xml.XPath import ParsedStep, ParsedAxisSpecifier, ParsedNodeTest
from Ft.Xml.XPath import Conversions, _comparisons
from Ft.Xml.XPath import XPathTypes as Types


class ParsedLiteralExpr:
    """
    An object representing a string literal expression
    (XPath 1.0 grammar production 29: Literal)
    """
    def __init__(self, literal):
        if len(literal) >= 2 and (literal[0] in ['\'', '"'] and
                                  literal[0] == literal[-1]):
            literal = literal[1:-1]
        self._literal = literal

    def evaluate(self, context):
        return self._literal

    def pprint(self, indent=''):
        print indent + str(self)

    def __str__(self):
        return '<Literal at %x: %s>' % (id(self), repr(self))

    def __repr__(self):
        return '"' + self._literal.encode('unicode_escape') + '"'


class ParsedNLiteralExpr(ParsedLiteralExpr):
    """
    An object representing a numeric literal expression
    (XPath 1.0 grammar production 30: Number)
    """
    def __init__(self, nliteral):
        self._nliteral = nliteral
        self._literal = float(nliteral)

    def pprint(self, indent=''):
        print indent + str(self)

    def __str__(self):
        return '<Number at %x: %s>' % (id(self), repr(self))

    def __repr__(self):
        if number.isnan(self._literal):
            return 'NaN'
        elif number.isinf(self._literal):
            if self._literal < 0:
                return '-Infinity'
            else:
                return 'Infinity'
        else:
            return str(self._nliteral)

class ParsedVariableReferenceExpr:
    """
    An object representing a variable reference expression
    (XPath 1.0 grammar production 36: VariableReference)
    """
    def __init__(self,name):
        self._name = name
        self._key = SplitQName(name[1:])
        return

    def evaluate(self, context):
        """Returns a string"""
        (prefix, local) = self._key
        if prefix:
            try:
                expanded = (context.processorNss[prefix], local)
            except KeyError:
                raise RuntimeException(RuntimeException.UNDEFINED_PREFIX,
                                       prefix)
        else:
            expanded = self._key
        try:
            return context.varBindings[expanded]
        except KeyError:
            raise RuntimeException(RuntimeException.UNDEFINED_VARIABLE,
                                   expanded[0], expanded[1])

    def pprint(self, indent=''):
        print indent + str(self)

    def __str__(self):
        return '<Variable at %x: %s>' % (id(self), repr(self))

    def __repr__(self):
        return self._name


def ParsedFunctionCallExpr(name, args):
    """
    Returns an object representing a function call expression
    (XPath 1.0 grammar production 16: FunctionCall)
    """
    name = XmlStrStrip(name)
    key = SplitQName(name)
    if not args:
        return FunctionCall(name, key, args)
    count = len(args)
    if count == 1:
        return FunctionCall1(name, key, args)
    elif count == 2:
        return FunctionCall2(name, key, args)
    elif count == 3:
        return FunctionCall3(name, key, args)
    else:
        return FunctionCallN(name, key, args)


class FunctionCall:
    """
    An object representing a function call expression
    (XPath 1.0 grammar production 16: FunctionCall)
    """
    def __init__(self, name, key, args):
        self._name = name
        self._key = key
        self._args = args
        self._func = None

    def pprint(self, indent=''):
        print indent + str(self)
        for arg in self._args:
            arg.pprint(indent + '  ')

    def error(self, *args):
        raise RuntimeException(RuntimeException.UNDEFINED_FUNCTION, self._name)

    def getArgumentError(self):
        if not inspect.isfunction(self._func):
            # We can only check for argument errors with Python functions
            return None

        argcount = len(self._args)

        args, vararg, kwarg = inspect.getargs(self._func.func_code)
        defaults = self._func.func_defaults or ()

        # Don't count the context parameter in argument count
        maxargs = len(args) - 1
        minargs = maxargs - len(defaults)

        if argcount > maxargs and not vararg:
            if maxargs == 0:
                return RuntimeException(RuntimeException.ARGCOUNT_NONE,
                                        self._name, argcount)
            elif defaults:
                return RuntimeException(RuntimeException.ARGCOUNT_ATMOST,
                                        self._name, maxargs, argcount)
            else:
                return RuntimeException(RuntimeException.ARGCOUNT_EXACT,
                                        self._name, maxargs, argcount)
        elif argcount < minargs:
            if defaults or vararg:
                return RuntimeException(RuntimeException.ARGCOUNT_ATLEAST,
                                        self._name, minargs, argcount)
            else:
                return RuntimeException(RuntimeException.ARGCOUNT_EXACT,
                                        self._name, minargs, argcount)

        # Not an error with arg counts for this function, use current error
        return None

    def evaluate(self, context):
        """Returns the result of calling the function"""
        func = self._func
        if func is None:
            (prefix, local) = self._key
            if prefix:
                try:
                    expanded = (context.processorNss[prefix], local)
                except:
                    raise RuntimeException(RuntimeException.UNDEFINED_PREFIX, prefix)
            else:
                expanded = self._key
            func = context.functions.get(expanded, self.error)
            if not ('nocache' in func.__dict__ and func.nocache):
                self._func = func
        try:
            result = func(context)
        except TypeError:
            exception = self.getArgumentError()
            if not exception:
                # use existing exception (empty raise keeps existing backtrace)
                raise
            raise exception

        #Expensive assert contributed by Adam Souzis.
        #No effect on Python running in optimized mode,
        #But would mean significant slowdown for developers, so disabled by default
        #assert not isinstance(result, list) or len(result) == len(Set.Unique(result))
        return result

    def __getinitargs__(self):
        return (self._name, self._key, self._args)

    def __getstate__(self):
        state = vars(self).copy()
        del state['_func']
        return state

    def __str__(self):
        return '<%s at %x: %s>' % (self.__class__.__name__, id(self), repr(self))

    def __repr__(self):
        result = self._name + '('
        if len(self._args):
            result = result + repr(self._args[0])
            for arg in self._args[1:]:
                result = result + ', ' + repr(arg)
        return result + ')'


class FunctionCall1(FunctionCall):
    # a function call with 1 argument
    def __init__(self, name, key, args):
        FunctionCall.__init__(self, name, key, args)
        self._arg0 = args[0]

    def evaluate(self, context):
        arg0 = self._arg0.evaluate(context)
        func = self._func
        if func is None:
            (prefix, local) = self._key
            if prefix:
                try:
                    expanded = (context.processorNss[prefix], local)
                except:
                    raise RuntimeException(RuntimeException.UNDEFINED_PREFIX, prefix)
            else:
                expanded = self._key
            func = context.functions.get(expanded, self.error)
            if not ('nocache' in func.__dict__ and func.nocache):
                self._func = func
        try:
            result = func(context, arg0)
        except TypeError:
            exception = self.getArgumentError()
            if not exception:
                # use existing exception (empty raise keeps existing backtrace)
                raise
            raise exception

        #Expensive assert contributed by Adam Souzis.
        #No effect on Python running in optimized mode,
        #But would mean significant slowdown for developers, so disabled by default
        #assert not isinstance(result, list) or len(result) == len(Set.Unique(result))
        return result


class FunctionCall2(FunctionCall):
    # a function call with 2 arguments
    def __init__(self, name, key, args):
        FunctionCall.__init__(self, name, key, args)
        self._arg0 = args[0]
        self._arg1 = args[1]

    def evaluate(self, context):
        arg0 = self._arg0.evaluate(context)
        arg1 = self._arg1.evaluate(context)
        func = self._func
        if func is None:
            (prefix, local) = self._key
            if prefix:
                try:
                    expanded = (context.processorNss[prefix], local)
                except:
                    raise RuntimeException(RuntimeException.UNDEFINED_PREFIX, prefix)
            else:
                expanded = self._key
            func = context.functions.get(expanded, self.error)
            if not ('nocache' in func.__dict__ and func.nocache):
                self._func = func
        try:
            result = func(context, arg0, arg1)
        except TypeError:
            exception = self.getArgumentError()
            if not exception:
                # use existing exception (empty raise keeps existing backtrace)
                raise
            raise exception

        #Expensive assert contributed by Adam Souzis.
        #No effect on Python running in optimized mode,
        #But would mean significant slowdown for developers, so disabled by default
        #assert not isinstance(result, list) or len(result) == len(Set.Unique(result))
        return result


class FunctionCall3(FunctionCall):
    # a function call with 3 arguments
    def __init__(self, name, key, args):
        FunctionCall.__init__(self, name, key, args)
        self._arg0 = args[0]
        self._arg1 = args[1]
        self._arg2 = args[2]

    def evaluate(self, context):
        arg0 = self._arg0.evaluate(context)
        arg1 = self._arg1.evaluate(context)
        arg2 = self._arg2.evaluate(context)
        func = self._func
        if func is None:
            (prefix, local) = self._key
            if prefix:
                try:
                    expanded = (context.processorNss[prefix], local)
                except:
                    raise RuntimeException(RuntimeException.UNDEFINED_PREFIX, prefix)
            else:
                expanded = self._key
            func = context.functions.get(expanded, self.error)
            if not ('nocache' in func.__dict__ and func.nocache):
                self._func = func
        try:
            result = func(context, arg0, arg1, arg2)
        except TypeError:
            exception = self.getArgumentError()
            if not exception:
                # use existing exception (empty raise keeps existing backtrace)
                raise
            raise exception

        #Expensive assert contributed by Adam Souzis.
        #No effect on Python running in optimized mode,
        #But would mean significant slowdown for developers, so disabled by default
        #assert not isinstance(result, list) or len(result) == len(Set.Unique(result))
        return result


class FunctionCallN(FunctionCall):
    # a function call with more than 3 arguments
    def __init__(self, name, key, args):
        FunctionCall.__init__(self, name, key, args)

    def evaluate(self, context):
        args = map(lambda arg, c=context: arg.evaluate(c), self._args)
        func = self._func
        if func is None:
            (prefix, local) = self._key
            if prefix:
                try:
                    expanded = (context.processorNss[prefix], local)
                except:
                    raise RuntimeException(RuntimeException.UNDEFINED_PREFIX, prefix)
            else:
                expanded = self._key
            func = context.functions.get(expanded, self.error)
            if not ('nocache' in func.__dict__ and func.nocache):
                self._func = func
        try:
            result = func(context, *args)
        except TypeError:
            exception = self.getArgumentError()
            if not exception:
                # use existing exception (empty raise keeps existing backtrace)
                raise
            raise exception

        #Expensive assert contributed by Adam Souzis.
        #No effect on Python running in optimized mode,
        #But would mean significant slowdown for developers, so disabled by default
        #assert not isinstance(result, list) or len(result) == len(Set.Unique(result))
        return result


########################################################################
# Nodeset Expressions
# Expressions that only return nodesets

class ParsedUnionExpr:
    """
    An object representing a union expression
    (XPath 1.0 grammar production 18: UnionExpr)
    """
    def __init__(self,left,right):
        self._left = left
        self._right = right

    def pprint(self, indent=''):
        print indent + str(self)
        self._left.pprint(indent + '  ')
        self._right.pprint(indent + '  ')

    def evaluate(self, context):
        """Returns a node-set"""
        left = self._left.evaluate(context)
        if not isinstance(left, Types.NodesetType):
            raise TypeError("%s must be a node-set, not a %s" % (repr(self._left),
                            Types.g_xpathPrimitiveTypes.get(type(left),
                            type(left).__name__)))

        right = self._right.evaluate(context)
        if not isinstance(right, Types.NodesetType):
            raise TypeError("%s must be a node-set, not a %s" % (repr(self._right),
                            Types.g_xpathPrimitiveTypes.get(type(right),
                            type(right).__name__)))

        set = Union(left, right)
        return set

    def __str__(self):
        return '<UnionExpr at %x: %s>' % (id(self), repr(self))

    def __repr__(self):
        return repr(self._left) + ' | ' + repr(self._right)


class ParsedPathExpr:
    """
    An object representing a path expression
    (XPath 1.0 grammar production 19: PathExpr)
    """
    def __init__(self, descendant, left, right):
        self._descendant = descendant
        self._left = left
        self._right = right
        return

    def pprint(self, indent=''):
        print indent + str(self)
        self._left.pprint(indent + '  ')
        self._right.pprint(indent + '  ')

    def _descendants(self, context, nodeset):
        for child in context.node.childNodes:
            context.node = child
            results = self._right.select(context)
            if not isinstance(results, Types.NodesetType):
                raise TypeError("%r must be a node-set, not a %s" % (
                    self._right,
                    Types.g_xpathPrimitiveTypes.get(type(results),
                                                    type(results).__name__)))
            if results:
                nodeset.extend(results)
            if child.nodeType == Node.ELEMENT_NODE:
                nodeset = self._descendants(context, nodeset)
        return nodeset

    def evaluate(self, context):
        """Returns a node-set"""
        #Evaluate the left, then, if op =//, the parsedStep.
        #Then evaluate the right, pushing the context each time.
        left = self._left.evaluate(context)
        if not isinstance(left, Types.NodesetType):
            raise TypeError("%r must be a node-set, not a %s" % (
                self._left,
                Types.g_xpathPrimitiveTypes.get(type(left),
                                                type(left).__name__)))

        state = context.copy()

        results = []
        for node in left:
            context.node = node
            nodeset = self._right.select(context)
            if not isinstance(nodeset, Types.NodesetType):
                raise TypeError("%r must be a node-set, not a %s" % (
                    self._right,
                    Types.g_xpathPrimitiveTypes.get(type(nodeset),
                                                    type(nodeset).__name__)))
            elif self._descendant:
                nodeset = self._descendants(context, nodeset)
            results.extend(nodeset)

        results = Unique(results)

        context.set(state)
        return results

    def __str__(self):
        return '<PathExpr at %x: %s>' % (id(self), repr(self))

    def __repr__(self):
        op = self._descendant and '//' or '/'
        return repr(self._left) + op + repr(self._right)


class ParsedFilterExpr:
    """
    An object representing a filter expression
    (XPath 1.0 grammar production 20: FilterExpr)
    """
    def __init__(self, filter_, predicates):
        self._filter = filter_
        self._predicates = predicates
        return

    def evaluate(self, context):
        """Returns a node-set"""
        #Evaluate our filter into a node set, filter that through the predicates.
        nodeset = self._filter.evaluate(context)
        if not isinstance(nodeset, Types.NodesetType):
            raise TypeError("%s must be a node-set, not a %s" % (repr(self._filter),
                            Types.g_xpathPrimitiveTypes.get(type(nodeset),
                            type(nodeset).__name__)))

        if nodeset:
            #In filter expressions, predicates are evaluated
            #with respect to the child axis, (XPath 2.4) therefore we must
            #sort into doc order before applying
            nodeset.sort()
            nodeset = self._predicates.filter(nodeset, context, reverse=0)
        return nodeset

    def pprint(self, indent=''):
        print indent + str(self)
        self._filter.pprint(indent + '  ')
        self._predicates.pprint(indent + '  ')

    def shiftContext(self,context,index,set,len,func):
        return func(context)

    def __str__(self):
        return '<FilterExpr at %x: %s>' % (id(self), repr(self))

    def __repr__(self):
        return repr(self._filter) + repr(self._predicates)


########################################################################
# Boolean Expressions
# Expressions that only return booleans

class ParsedOrExpr:
    """
    An object representing an or expression
    (XPath 1.0 grammar production 21: OrExpr)
    """
    def __init__(self, left, right):
        self._left = left
        self._right = right

    def pprint(self, indent=''):
        print indent + str(self)
        self._left.pprint(indent + '  ')
        self._right.pprint(indent + '  ')

    def evaluate(self, context):
        """Returns a boolean"""
        rt = Conversions.BooleanValue(self._left.evaluate(context))
        if not rt:
            rt = Conversions.BooleanValue(self._right.evaluate(context))
        return rt

    def __str__(self):
        return '<OrExpr at %x: %s>' % (id(self), repr(self))

    def __repr__(self):
        return repr(self._left) +' or ' + repr(self._right)


class ParsedAndExpr:
    """
    An object representing an and expression
    (XPath 1.0 grammar production 22: AndExpr)
    """
    def __init__(self,left,right):
        self._left = left
        self._right = right

    def pprint(self, indent=''):
        print indent + str(self)
        self._left.pprint(indent + '  ')
        self._right.pprint(indent + '  ')

    def evaluate(self, context):
        """Returns a boolean"""

        rt = Conversions.BooleanValue(self._left.evaluate(context))
        if rt:
            rt = Conversions.BooleanValue(self._right.evaluate(context))
        return rt

    def __str__(self):
        return '<AndExpr at %x: %s>' % (id(self), repr(self))

    def __repr__(self):
        return repr(self._left) + ' and ' + repr(self._right)


def _nodeset_compare(compare, a, b, relational=False):
    """
    Applies a comparison function to node-sets a and b
    in order to evaluate equality (=, !=) and relational (<, <=, >=, >)
    expressions in which both objects to be compared are node-sets.

    Returns an XPath boolean indicating the result of the comparison.
    """
    if isinstance(a, Types.NodesetType) and isinstance(b, Types.NodesetType):
        # From XPath 1.0 Section 3.4:
        # If both objects to be compared are node-sets, then the comparison
        # will be true if and only if there is a node in the first node-set
        # and a node in the second node-set such that the result of
        # performing the comparison on the string-values of the two nodes
        # is true.
        #
        # (Note, however, that relational comparisons convert their operands
        # to numbers.)
        if not(a and b):
            # One of the two node-sets is empty.  In this case, according to
            # section 3.4 of the XPath rec, no node exists in one of the two
            # sets to compare, so *any* comparison must be false.
            return boolean.false
        elif relational:
            # relational, and both node-sets are nonempty
            coerce = Conversions.NumberValue
        else:
            # not relational, and both node-sets are nonempty
            coerce = Conversions.StringValue

        # convert the larger set to strings or numbers one time,
        # then iterate over the smaller set, comparing to each item in
        # the converted larger set.
        if len(a) > len(b):
            coerced = [coerce(node) for node in a]
            nodes = b
        else:
            coerced = [coerce(node) for node in b]
            nodes = a
        for node in nodes:
            current = coerce(node)
            for value in coerced:
                if compare(value, current):
                    return boolean.true
        return boolean.false

    # From XPath 1.0 Section 3.4:
    # If one object to be compared is a node-set and the other is a number,
    # then the comparison will be true if and only if there is a node in the
    # node-set such that the result of performing the comparison on the
    # number to be compared and on the result of converting the string-value
    # of that node to a number using the number function is true. If one
    # object to be compared is a node-set and the other is a string, then the
    # comparison will be true if and only if there is a node in the node-set
    # such that the result of performing the comparison on the string-value
    # of the node and the other string is true. If one object to be compared
    # is a node-set and the other is a boolean, then the comparison will be
    # true if and only if the result of performing the comparison on the
    # boolean and on the result of converting the node-set to a boolean using
    # the boolean function is true.
    #
    # (In other words, coerce each node to the same type as the other operand,
    # then compare them. Note, however, that relational comparisons convert
    # their operands to numbers.)
    if isinstance(a, Types.NodesetType):
        # a is nodeset
        if isinstance(b, Types.BooleanType):
            coerce = Conversions.BooleanValue
        elif relational:
            b = Conversions.NumberValue(b)
            coerce = Conversions.NumberValue
        elif isinstance(b, Types.NumberType):
            coerce = Conversions.NumberValue
        else:
            b = Conversions.StringValue(b)
            coerce = Conversions.StringValue
        for node in a:
            if compare(coerce(node), b):
                return boolean.true
    else:
        # b is nodeset
        if isinstance(a, Types.BooleanType):
            coerce = Conversions.BooleanValue
        elif relational:
            a = Conversions.NumberValue(a)
            coerce = Conversions.NumberValue
        elif isinstance(a, Types.NumberType):
            coerce = Conversions.NumberValue
        else:
            a = Conversions.StringValue(a)
            coerce = Conversions.StringValue
        for node in b:
            if compare(a, coerce(node)):
                return boolean.true

    return boolean.false


class ParsedEqualityExpr:
    """
    An object representing an equality expression
    (XPath 1.0 grammar production 23: EqualityExpr)
    """
    def __init__(self, op, left, right):
        self._op = op
        self._left = left
        self._right = right
        if op == '=':
            self._cmp = _comparisons.eq
        else:
            self._cmp = _comparisons.ne

    def __getstate__(self):
        return (self._op, self._left, self._right)

    def __setstate__(self, state):
        self.__init__(*state)

    def evaluate(self, context):
        """Returns a boolean"""
        left = self._left.evaluate(context)
        right = self._right.evaluate(context)

        if isinstance(left, Types.NodesetType) or \
           isinstance(right, Types.NodesetType):
            return _nodeset_compare(self._cmp, left, right)

        # From XPath 1.0 Section 3.4:
        # order for equality expressions when neither is a node-set
        # 1. either is boolean, both are converted as if by boolean()
        # 2. either is number, both are converted as if by number()
        # otherwise, both are converted as if by string()
        if isinstance(left, Types.BooleanType) or \
           isinstance(right, Types.BooleanType):
            coerce = Conversions.BooleanValue
        elif isinstance(left, Types.NumberType) or \
             isinstance(right, Types.NumberType):
            coerce = Conversions.NumberValue
        else:
            coerce = Conversions.StringValue

        result = self._cmp(coerce(left), coerce(right))
        return result and boolean.true or boolean.false

    def pprint(self, indent=''):
        print indent + str(self)
        self._left.pprint(indent + '  ')
        self._right.pprint(indent + '  ')

    def __str__(self):
        return '<EqualityExpr at %x: %s>' % (id(self), repr(self))

    def __repr__(self):
        if self._op == '=':
            op = ' = '
        else:
            op = ' != '
        return repr(self._left) + op + repr(self._right)



class ParsedRelationalExpr:
    """
    An object representing a relational expression
    (XPath 1.0 grammar production 24: RelationalExpr)
    """
    def __init__(self, opcode, left, right):
        self._op = opcode
        self._left = left
        self._right = right

        if opcode == 0:
            self._cmp = _comparisons.lt
        elif opcode == 1:
            self._cmp = _comparisons.le
        elif opcode == 2:
            self._cmp = _comparisons.gt
        elif opcode == 3:
            self._cmp = _comparisons.ge
        return

    def __getstate__(self):
        return (self._op, self._left, self._right)

    def __setstate__(self, state):
        self.__init__(*state)

    def evaluate(self, context):
        """Returns a boolean"""
        left = self._left.evaluate(context)
        right = self._right.evaluate(context)

        if isinstance(left, Types.NodesetType) or \
           isinstance(right, Types.NodesetType):
            return _nodeset_compare(self._cmp, left, right, relational=True)

        a = Conversions.NumberValue(left)
        b = Conversions.NumberValue(right)
        return self._cmp(a, b) and boolean.true or boolean.false

    def pprint(self, indent=''):
        print indent + str(self)
        if type(self._left) == types.InstanceType:
            self._left.pprint(indent + '  ')
        else:
            print indent + '  ' + '<Primitive: %s>' % str(self._left)
        if type(self._right) == types.InstanceType:
            self._right.pprint(indent + '  ')
        else:
            print indent + '  ' + '<Primitive: %s>' % str(self._right)

    def __str__(self):
        return '<RelationalExpr at %x: %s>' % (id(self), repr(self))

    def __repr__(self):
        if self._op == 0:
            op = ' < '
        elif self._op == 1:
            op = ' <= '
        elif self._op == 2:
            op = ' > '
        elif self._op == 3:
            op = ' >= '
        return repr(self._left) + op + repr(self._right)

########################################################################
# Number Expressions
# Expressions that only return numbers (float)

class ParsedAdditiveExpr:
    """
    An object representing an additive expression
    (XPath 1.0 grammar production 25: AdditiveExpr)
    """
    def __init__(self, sign, left, right):
        self._sign = sign
        self._leftLit = 0
        self._rightLit = 0
        if isinstance(left, ParsedLiteralExpr):
            self._leftLit = 1
            self._left = Conversions.NumberValue(left.evaluate(None))
        else:
            self._left = left
        if isinstance(right, ParsedLiteralExpr):
            self._rightLit = 1
            self._right = Conversions.NumberValue(right.evaluate(None))
        else:
            self._right = right
        return

    def evaluate(self, context):
        '''Returns a number'''
        if self._leftLit:
            lrt = self._left
        else:
            lrt = self._left.evaluate(context)
            lrt = Conversions.NumberValue(lrt)
        if self._rightLit:
            rrt = self._right
        else:
            rrt = self._right.evaluate(context)
            rrt = Conversions.NumberValue(rrt)
        return lrt + (rrt * self._sign)

    def pprint(self, indent=''):
        print indent + str(self)
        if type(self._left) == types.InstanceType:
            self._left.pprint(indent + '  ')
        else:
            print indent + '  ' + '<Primitive: %s>' % str(self._left)
        if type(self._right) == types.InstanceType:
            self._right.pprint(indent + '  ')
        else:
            print indent + '  ' + '<Primitive: %s>' % str(self._right)

    def __str__(self):
        return '<AdditiveExpr at %x: %s>' % (id(self), repr(self))

    def __repr__(self):
        if self._sign > 0:
            op = ' + '
        else:
            op = ' - '
        return repr(self._left) + op + repr(self._right)


class ParsedMultiplicativeExpr:
    """
    An object representing an multiplicative expression
    (XPath 1.0 grammar production 26: MultiplicativeExpr)
    """
    def __init__(self, opcode, left, right):
        self._op = opcode
        self._left = left
        self._right = right

    def evaluate(self, context):
        '''Returns a number'''
        lrt = self._left.evaluate(context)
        lrt = Conversions.NumberValue(lrt)
        rrt = self._right.evaluate(context)
        rrt = Conversions.NumberValue(rrt)
        res = 0
        # multiply
        if self._op == 0:
            res = lrt * rrt
        # divide
        elif self._op == 1:
            try:
                res = lrt / rrt
            except ZeroDivisionError:
                if lrt < 0:
                    res = -number.inf
                elif lrt == 0:
                    res = number.nan
                else:
                    res = number.inf
        # modulo
        elif self._op == 2:
            try:
                res = lrt % rrt
            except ZeroDivisionError:
                res = number.nan
        return res

    def pprint(self, indent=''):
        print indent + str(self)
        if type(self._left) == types.InstanceType:
            self._left.pprint(indent + '  ')
        else:
            print indent + '  ' + '<Primitive: %s>' % str(self._left)
        if type(self._right) == types.InstanceType:
            self._right.pprint(indent + '  ')
        else:
            print indent + '  ' + '<Primitive: %s>' % str(self._right)

    def __str__(self):
        return '<MultiplicativeExpr at %x: %s>' % (id(self), repr(self))

    def __repr__(self):
        if self._op == 0:
            op = ' * '
        elif self._op == 1:
            op = ' div '
        elif self._op == 2:
            op = ' mod '
        try:
            return repr(self._left) + op + repr(self._right)
        except:
            print type(self._left)
            print type(op), op
            print type(repr(self._right))
            raise



class ParsedUnaryExpr:
    """
    An object representing a unary expression
    (XPath 1.0 grammar production 27: UnaryExpr)
    """
    def __init__(self, exp):
        self._exp = exp

    def evaluate(self, context):
        '''Returns a number'''
        exp = self._exp.evaluate(context)
        exp = Conversions.NumberValue(exp)
        return exp * -1.0

    def pprint(self, indent=''):
        print indent + str(self)

    def __str__(self):
        return '<UnaryExpr at %x: %s>' % (id(self), repr(self))

    def __repr__(self):
        return '-' + repr(self._exp)
