CREATE OR REPLACE FUNCTION check_phone_number(text)
RETURNS boolean AS $$
BEGIN
  IF NOT $1 ~  e'^\\+45\\ \\d{4}\\ \\d{4}$' THEN
    RAISE EXCEPTION 'Wrong formated string "%". Expected format is +45 XXXX XXXX', $1;
  END IF;
  RETURN true; 
END;
$$ LANGUAGE plpgsql;

CREATE OR REPLACE FUNCTION generate_string(integer) RETURNS SETOF varchar AS $$
BEGIN
  FOR _i IN 1 .. $1 LOOP 
    RETURN NEXT '<a href="slides'||_i||'.pdf">Slides for Lecture #'||_i||'</a>';
  END LOOP;
  RETURN;
END; $$ LANGUAGE plpgsql;

CREATE OR REPLACE FUNCTION html_li_aggr (state text,p text) RETURNS text AS $$
  BEGIN
    IF p IS NULL THEN
      RETURN state;
    ELSE
      RETURN state || '<li>' || p || E'</li>\n';
    END IF;
  END;
$$ LANGUAGE plpgsql IMMUTABLE;

CREATE OR REPLACE FUNCTION html_ul_final (state text) RETURNS text AS $$
  BEGIN
    IF $1 <> '' THEN
      RETURN E'<ul>\n' || state || '</ul>';
    ELSE
      RETURN '';
    END IF;
  END;
$$ LANGUAGE plpgsql IMMUTABLE;

DROP AGGREGATE html_ul (text);

CREATE AGGREGATE html_ul (
  basetype = text,
  sfunc = html_li_aggr,
  stype = text,
  initcond = '',
  finalfunc = html_ul_final
);

CREATE OR REPLACE FUNCTION tabsin(x float)
RETURNS float AS $$
DECLARE sinx float;
BEGIN
  IF NOT EXISTS(SELECT relname FROM pg_class WHERE relname = 'tabsin' AND relkind = 'r' AND pg_table_is_visible(oid)) THEN
    RAISE NOTICE 'Create table tabsin';
    CREATE TEMP TABLE tabsin (val NUMERIC PRIMARY KEY, sine NUMERIC);
  END IF;
  SELECT INTO sinx sine FROM tabsin WHERE val = x;
  IF sinx IS NULL THEN
    sinx := SIN(x);
    INSERT INTO tabsin VALUES (x, sinx);
  END IF;
  RETURN sinx; 
END;
$$ LANGUAGE plpgsql;

CREATE OR REPLACE FUNCTION fib(n int)
RETURNS int AS $$
BEGIN
  IF n < 2 THEN
    RETURN N;
  END IF;
  RETURN tabfib(n-1) + tabfib(n-2);
END;
$$ LANGUAGE plpgsql;

CREATE OR REPLACE FUNCTION tabfib(n int)
RETURNS int AS $$
DECLARE fibn int;
BEGIN
  IF NOT EXISTS(SELECT relname FROM pg_class WHERE relname = 'tabfib' AND relkind = 'r' AND pg_table_is_visible(oid)) THEN
    RAISE NOTICE 'Create table tabfib';
    CREATE TEMP TABLE tabfib (val NUMERIC PRIMARY KEY, fib NUMERIC);
  END IF;
  SELECT INTO fibn fib FROM tabfib WHERE val = n;
  IF fibn IS NULL THEN
    fibn := fib(n);
    INSERT INTO tabfib VALUES (n, fibn);
  END IF;
  RETURN fibn; 
END;
$$ LANGUAGE plpgsql;