requirePostParam :: Text -> Text -> Handler Text
requirePostParam pam errstr = lookupPostParam pam >>= \mv -> case mv of
    Nothing -> invalidArgsI [errstr]
    Just v  -> return v
requirePostParam :: Text -> Text -> Handler Text
requirePostParam pam errstr = lookupPostParam pam >>= \mv -> case mv of
    Nothing -> invalidArgsI [errstr]
    Just v  -> return v
requirePostParam pam errstr = lookupPostParam pam >>= \mv -> case mv of
    Nothing -> invalidArgsI [errstr]
    Just v  -> return v