Quote from: aes1 on April 17, 2013, 07:58:34 AM

Exchanges commonly have two options for buying and selling: limit orders (executed only at the specified price or better) and market orders (executed immediately or not at all).

So, a stupid reductionist idea: why do we need the two different types? Why not just use limit orders?

Pros:
- it would make the user interface simpler - the user wouldn't have to think of options
- it would make the trade engine simpler (and therefore easier to optimize, verify, and test)

Cons:
- but that's not what we are used to!
- Huh

The user interface would, by default, calculate the price which is needed for the limit order to be executed completely at a high probability (i.e. the market doesn't suddenly move into the wrong direction), and have that set as a default. And that's a "market order" for you.

A market order is either a sell at $0 or a buy at $inf as far as the trading engine is concerned. You won't be selling at 0 or buying at $inf because it matches bids so you get the best deal. However, there's no extra complexity in a market order.