You need to introduce a do
block after the else
like so:
else do let myTrades = process myData
conn <- connectSqlite3 "trades.db"
insert <- DB.prepare conn "INSERT INTO trades VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?);"
DB.executeMany insert $ map (\xs -> map DB.toSql xs) myTrades
DB.commit conn
DB.disconnect conn