Create function problem

Hello

I cannot write new function with local variables:

CREATE FUNCTION "get_new_id1" () RETURNS bigint AS'
declare
id bigint;
begin
id:=nextval(\'id_sequence\'::text);
return id;
end;
'LANGUAGE 'sql' VOLATILE ;

Error message see when compiling:

ERROR: parser: parse error at or near "bigint" at character 16

That I do wrong?

Best regards,
Yaroslav Ulyanov
yulyanov(at)mera(dot)ru