Subqueries must be enclosed in parentheses. The parentheses that are part of the function call do not count.
Ah! Thank you David, this has worked now -
CREATE OR REPLACE FUNCTION words_solve_puzzle(
in_mid bigint,
in_uid int,
in_guess text,
OUT out_json jsonb
) RETURNS jsonb AS
$func$
DECLARE
_tile jsonb;
_letter char;
_value integer;
BEGIN
in_guess := UPPER(in_guess);
FOR _tile IN SELECT * FROM JSONB_ARRAY_ELEMENTS((SELECT tiles FROM words_moves WHERE mid = in_mid))
LOOP
_letter := _tile->>'letter';
_value := (_tile->>'value')::int;
-- verify that all played tiles except wildcard are found in the suggested answer
IF _value > 0 AND POSITION(_letter IN in_guess) = 0 THEN
out_json := json_build_object(
'label', '👎 Keep guessing!'
);
RETURN;
END IF;
END LOOP;
-- check if the in_guess is one of the played words in that move
IF NOT EXISTS(SELECT 1 FROM words_scores WHERE mid = in_mid AND word = in_guess) THEN
out_json := json_build_object(
'label', '👎 Wrong!'
);
RETURN;
END IF;
-- the solution already submitted, just ack, but do not award coins
IF EXISTS (SELECT 1 FROM words_puzzles WHERE mid = in_mid AND uid = in_uid) THEN
out_json := json_build_object(
'label', '👍 Correct!',
'url', '/ws/puzzle2?mid=' || in_mid || '&secret=' || MD5(in_mid || 'my secret')
);
RETURN;
END IF;
-- save the puzzle solution and award coins to the user
INSERT INTO words_puzzles (mid, uid, solved)
VALUES (in_mid, in_uid, CURRENT_TIMESTAMP);
UPDATE words_users
SET coins = coins + 1
WHERE uid = in_uid;
out_json := json_build_object(
'label', '👍 Correct, +1 coin!',
'url', '/ws/puzzle2?mid=' || in_mid || '&secret=' || MD5(in_mid || 'my secret')
);
END
$func$ LANGUAGE plpgsql;
P.S. 'my secret' is not my real secret passphrase :-)