Complex Validation Example in Erlang

validation.erl

%
% store all necessary data to pass between validators in
% #validator_state struct
%
run_checks(FunList, Data) ->
	run_checks(FunList, Data, #validator_state{}).

%
% evaluate validation chain
%
run_checks([], Data, State) ->
	{valid, Data, State};
run_checks([F | FunList], Data, State) ->
	case ?MODULE:F(Data, State) of
	{valid, NewData, NewState} ->
		run_checks(FunList, NewData, NewState);
	Error = {error, _ErrorMsg, _NewState} ->
		% you can add to error reporting in WHICH
		% validator it failed
		% like
		% {error, F, _ErrorMsg, _NewState}
		Error
	% for ease of programming validators I would add also
	% shortcut return codes like
	% valid -> run_checks(FunList, Data, State);
	% and
         % {error, Error} -> {error, Error, State};
	end.

And I will end up with functions like

% check functions
check_email(PropList, State) ->
	do something and return values ....
check_name(PropList, State) ->
	do something and return values ....