samer@4: function [f,Y]=history_nest(fields,dim,H)
samer@4: % history_nest - return state transformer that logs old states
samer@4: %
samer@4: % history :: 
samer@4: %    F:{[N]->string}  ~'list of field names',
samer@4: %    natural          ~'dimension to cat along (defaults to 1)',
samer@4: %    struct F         ~'old history to build on'
samer@4: % -> (history(A,F) ->history(A,F)),
samer@4: %    history(A,F).
samer@4: %
samer@4: % history(A,F) ~ 'structure A with history of fields F' ::= 
samer@4: %    struct { 
samer@4: %       current :: struct A ~'original fields from A'; 
samer@4: %       history :: struct F ~ 'sub-struct containing fields F'
samer@4: %    }.
samer@4: %
samer@4: % This function returns a state transformer function. The state MUST be
samer@4: % a structure but it can have any fields. The history mechanism adds the
samer@4: % field 'history' which contains the histories of certain fields from 
samer@4: % the main structure. The returned function concatenates the current
samer@4: % values of the named fields onto the end of the corresponding fields
samer@4: % in the history, if X is a sequence whose elements contain a field 
samer@4: % called 'cost', then
samer@4: %
samer@4: %   [logcost,H0]=history({'cost'},1);
samer@4: %   Y=scandata(logcost,H0,X);
samer@4: %
samer@4: % Elements of Y will have fields 'current' and 'history' which
samer@4: % contain values from X and a history of 'cost' respectively.
samer@4: 
samer@4: 	g=@logfields_scanner;
samer@4: 	if nargin<2, dim=1; end
samer@4: 	if nargin<3, H=struct; end
samer@4: 
samer@4: 	for i=1:length(fields)
samer@4: 		% initialise history fields if not present already
samer@4: 		if ~isfield(H,fields{i}),
samer@4: 			H.(fields{i}) = [];
samer@4: 		end
samer@4: 	end
samer@4: 	
samer@4: 	f=@logfields;
samer@4: 	Y.current=[];
samer@4: 	Y.history=H;
samer@4: 
samer@4: 	function Y=logfields(Y,X)
samer@4: 		Y.current=X;
samer@4: 		Y.history=logfields_scanner(Y.history,X);
samer@4: 	end
samer@4: 
samer@4: 	function H=logfields_scanner(H,X)
samer@4: 		for i=1:length(fields)
samer@4: 			field=fields{i};
samer@4: 			H.(field) = cat(dim,H.(field),X.(field));
samer@4: 		end
samer@4: 	end
samer@4: end
samer@4: 	
samer@4: 	
samer@4: 
samer@4: