[erlang-questions] Simple (dumb :) pattern matching question

[Pat e]

How can i put a pattern match from a yaws form:

{"formsend","process data"} where i want to extract "process data" from list:

out(A) ->
	
	R = yaws_api:parse_post(A),
	P(H) = ({I,H} = {R}),
	L = mnesia:dirty_read(test,R),
	{html, f("~p", [P])}.

P(H) line gives a statement: "illegal pattern" in yaws and nothing else?? (:(

I looked at the doc's but unfortunately i can't understand the right
way to go... for simple pattern matching there is only REPL sample:

5> {X, Y} = {2, 3}.
{2,3}
6> Y.
3

.... how do i have to form it in editor?