text: # LICENSE --------------------------------------------------------------------
  # Copyright 2017 Jesse A. Hostetler
  #
  # Redistribution and use in source and binary forms, with or without
  # modification, are permitted provided that the following conditions are met:
  #
  # 1. Redistributions of source code must retain the above copyright notice, this
  # list of conditions and the following disclaimer.
  #
  # 2. Redistributions in binary form must reproduce the above copyright notice,
  # this list of conditions and the following disclaimer in the documentation
  # and/or other materials provided with the distribution.
  #
  # THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
  # AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  # IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
  # DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
  # FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  # DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
  # SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
  # CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
  # OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  # ----------------------------------------------------------------------------
  
  from csvq.relation import Attribute, Relation, Row
  
  # ----------------------------------------------------------------------------
  
  class Map(Relation):
  	def __init__( self, in_relation, fd ):
  		super().__init__( attributes = tuple(fd) )
  		self._in_relation = in_relation
  		self._itr = iter(in_relation)
  		self._fs = tuple( fd.values() )
  		
  	def __next__( self ):
  		t = next(self._itr)
  		return tuple( f( Row( self._in_relation, t ) ) for f in self._fs )
  		
  	def __iter__( self ):
  		return self
  		
  # ----------------------------------------------------------------------------
  
  class Update(Relation):
  	def __init__( self, in_relation, fd ):
  		# for k in fd:
  			# if in_relation.attribute( k.name() ) != k:
  				# raise TypeError( "Incompatible attribute definitions" )
  		super().__init__( attributes = in_relation._attributes, index = in_relation._index )
  		self._itr = iter(in_relation)
  		self._idx = tuple( self.index( k ) for k in fd )
  		self._fs = tuple( fd.values() )
  		
  	def __next__( self ):
  		t = next(self._itr)
  		tprime = list( t )
  		for (i, f) in enumerate(self._fs):
  			tprime[self._idx[i]] = f( Row( self, t ) )
  		return tuple( tprime )
  		
  	def __iter__( self ):
  		return self
  		
  # ----------------------------------------------------------------------------
  
  class Fold(Relation):
  	def __init__( self, in_relation, fd ):
  		super().__init__( attributes = tuple(fd) )
  		self._in_relation = in_relation
  		self._fs = tuple( f for (f, v) in fd.values() )
  		self._v  = list( v for (f, v) in fd.values() )
  		
  	def __iter__( self ):
  		for t in self._in_relation:
  			for i in range(0, len(self._v)):
  				self._v[i] = self._fs[i]( self._v[i], Row( self._in_relation, t ) )
  		yield tuple( self._v )
  