[define_tag( 'list',
			-namespace	= 'field',
			-optional	= 'params',-copy,
			-optional	= 'mode',
			-description= '[field_list] - Compare action_params with the datasource'
			);

			//	returns: set
			//	-params: An array of pairs (typically action_params)
			//	-mode == 'missing'		=	returns set - missing fields 
			//	-mode == 'unused'		=	returns set - unused fields (not updated/searched on etc)
			//	-mode == 'difference'	=	returns set - difference between source and target field sets
			//	-mode else				=	returns set - target's fields
			
	fail_if: (local:'params')->type != 'array',-2, #_ref': Requires an array of pairs (action_params)';
	
	!(local_defined:'mode')	? local:'mode'='default';
	
	local:'_copyParams'	= '-Database,-Table,-Layout'->split(',');
	local:'_actionFields'	= set;
	local:'_inline'			= array;
	local:'_ref'			= 'field_'+tag_name;
	
	//	Seperate fields from "-params"
	iterate:#params,(local:'pair');
		local:'_param'	= string(#pair->get(1));
		local:'_value'	= string(#pair->get(2));
		
		#_param->beginsWith('-')=='false'?
			#_actionFields->insert(#_param)
				| (#_copyParams >> #_param ? #_inline->insert(#_param = #_value));				
	/iterate;
	
	fail_if: #_inline->size == 0		, -2, #_ref': Missing schema params';
	fail_if: #_inline !>> '-Database'	, -2, #_ref': database param';
	fail_if: #_inline !>> '-Layout' && #_inline !>> '-Table' , -2, #_ref': Missing -table or -layout param';
	
	//	Pull true field names
	inline:#_inline,-show;
		local:'_tableFields' = set;
		#_tableFields->insertFrom(field_names->iterator);
	/inline;
	
	if:#mode == 'missing';
		local:'_missing'=set;
		iterate:#_actionFields,(local:'_param');
			#_tablefields !>> #_param ? #_missing->insert(#_param);
		/iterate;				
		return:#_missing;
		
	else:#mode == 'unused';
		local:'_unused'=set;
		iterate:#_tablefields,(local:'_param');
			#_actionFields !>> #_param ? #_unused->insert(#_param);
		/iterate;
		return:#_unused;	
				
	else:#mode == 'difference';			
		return:#_tableFields->difference(#_actionFields);

	else;
		fail:-2,Namespace_Current #_ref': Unknown mode: '#mode;
	/if;
	
/define_tag]