Option

In financial dealings, an option is (listen very carefully now): the right but not the obligation to buy or sell something at a certain strike price at or by a certain expiry date.

The fundamental things you need to know regarding options are as follows: you need to know what the difference between a call option and a put option is, and the difference between an American style option and a European style option.

There are other types of options but those are not plain vanilla, and fit under the exotic financial derivates category...

They're called lots of things in different games (eg, bits in R-Type, sprites in Super Aleste, etc), but to make life easier for reviewers, there's a convention of calling them 'options', since that's what they were named in Gradius, the game that made them an obligatory feature in shmups.

See also: droid, power-up.

If you are using a font that supports the full Macintosh character set, you can use key combinations with this key to generate accented letters, other non-English letters (such as the German sharp-S, or the oe and ae ligatures), and a small range of other symbols: smart quotes and European quotes, dagger and double dagger signs, and a few mathematical symbols.

Under Mac OS X, the range of typable characters is greatly expanded through the Extended Roman and Unicode input modes.

datatype 'a option = SOME of 'a | NONE

lookup : (int * string) list -> int -> string option

This is particularly important when we're handling a value returned by a partial function. By the very nature of sum types, we can't do anything with the option itself besides case on whether it's a SOME or a NONE. Thus, we are forced to handle the case where the element is not found in the list, or malloc can't give us the memory we asked for.

In C, for example, instead of returning NONE, we just return a special value that indicates that we shouldn't use the value we got and that we need some special error handling. Of course, it is still a value of the type we were expecting, so there's nothing forcing us to handle that special case. This is what gets us into trouble most of the time -- trying to dereference a NULL pointer, for example. If malloc just returned NONE instead of NULL and SOME(p) instead of just the pointer, we would have no choice but to case on NONE or SOME and handle each appropriately, since that's literally all we can do with an option, or any sum type, for that matter.

This distinction (or lack thereof) gets us into trouble in the real world, too. People vie to get the vanity plate that says "NONE", since an officer taking down their plate number would write "NONE", when they really mean SOME("NONE") (of type string option), not NONE, as they're likely to confuse it to mean later.

Op"tion (?), n. [L. optio; akin to optare to choose, wish, optimus best, and perh. to E. apt: cf. F. option.]

1.

The power of choosing; the right of choice or election; an alternative.

There is an option left to the United States of America, whether they will be respectable and prosperous, or contemptible and miserable, as a nation. Washington.

2.

The exercise of the power of choice; choice.

Transplantation must proceed from the option of the people, else it sounds like an exile. Bacon.

3.

A wishing; a wish.

Bp. Hall.

4. Ch. of Eng.

A right formerly belonging to an archbishop to select any one dignity or benefice in the gift of a suffragan bishop consecrated or confirmed by him, for bestowal by himself when next vacant; -- annulled by Parliament in 1845.

5. Stock Exchange

A stipulated privilege, given to a party in a time contract, of demanding its fulfillment on any day within a specified limit.

Buyer's option, an option allowed to one who contracts to buy stocks at a certain future date and at a certain price, to demand the delivery of the stock (giving one day's notice) at any previous time at the market price. -- Seller's option, an option allowed to one who contracts to deliver stock art a certain price on a certain future date, to deliver it (giving one day's notice) at any previous time at the market price. Such options are privileges for which a consideration is paid. -- Local option. See under Local.

Syn. -- Choice; preference; selection. -- Option, Choice. Choice is an act of choosing; option often means liberty to choose, and implies freedom from constraint in the act of choosing.

© Webster 1913.