"Meta"-Trader 4 (MQ4)

This is a popular platform for private traders and provided by most brokers. The MQ4 script language of its "Expert Advisors" (EAs) is based on C, which would theoretically allow easy conversion to Zorro's lite-C. Unfortunately, MQ4 has many issues that make "Expert Advisors" a lot more complex and difficult to handle than scripts of other platforms.

The MQ4 main script runs at every tick. This means that the last price candle is normally incomplete, so indicators in EAs return a different value than the same indicators in other platforms. For fixing this, the EA must check if the candle is complete, or the indicator must be shifted so that its last value is from the previous candle. Trades are not managed by the platform, but must be managed by code in the script. Series are not natively supported, but emulated with loops and functions. Indicators often produce different results in MQ4 than in other platforms because the MQ4 standard indicators do not use their standard algorithms, but special MQ4 variants. Time zones and account parameters are not normalized, so EAs must be individually adapted to the broker. To complicate matters further, MQ4 does not use common trade units such as lots and pips, but calculates with "standard lots" and "points" that need to be multiplied with account-dependent conversion factors. Most code in an EA is therefore not used for the trade algorithm, but for working around all those problems. This results in the long and complex 'spaghetti code' that is typical for EAs.