Learning Exercise
The discriminated union type represents a fixed number of named cases. Each value of a discriminated union corresponds to exactly one of the named cases.
A discriminated union is defined using the type keyword, with cases separated by pipe (|) characters:
type Season =
| Spring
| Summer
| Autumn
| Winter
Each case of a discriminated union can optionally have data associated with it, and different cases can have different types of data. If none of the cases have data associated with them, the discriminated union is similar to what other languages usually refer to as an enumeration (or enum).
type Number =
| Integer of int
| Float of float
| Invalid
Creating a value for a specific case can be done by referring to its name (e.g, Success). As case names are just constructor functions, associated data can be passed as a regular function argument. If another discriminated union has defined a case with the same name, you'll need to use its full name (e.g. Result.Success).
let byName = Integer 2
let byFullName = Number.Invalid
Discriminated unions have structural equality, which means that two values for the same case and with the same (optional) data are equivalent.
While one can use if/elif/else expressions to work with discriminated unions, the recommended way to work with them is through pattern matching using the identifier pattern:
let describe number =
match number with
| Integer i -> sprintf "Integer: %d" i
| Float d -> sprintf "Float: %f" d
| Invalid -> "Invalid"
In this exercise, it's Valentine's day and you and your partner are planning on doing something nice together. Your partner has lots of ideas, and is now asking you to rate the ideas, in order to find the activity to engage in.
The following ideas are proposed by your partner:
You have six tasks to help choose your Valentine's day activity.
For each idea your partner proposes, you respond with one of three options: yes, no or maybe.
Define the Approval discriminated union to represent these options as the following three cases: Yes, No and Maybe.
Your partner has selected two possible restaurants: one based on the Korean cuisine and the other based on the Turkish cuisine.
Define the Cuisine discriminated union to represent these cuisines as the following two cases: Korean and Turkish.
There are tons of movies to choose from, so to narrow things down, your partner also lists their genre.
Define the Genre discriminated union to represent the following genres as cases: Crime, Horror, Romance and Thriller.
As said, your partner has come up with five different activities: playing a board game, chill out, watch a movie, go to a restaurant and taking a walk.
Define the Activity discriminated union to represent these activity types:
BoardGame: no associated data.Chill: no associated data.Movie: has its Genre as associated data.Restaurant: has its Cuisine as associated data.Walk: has an int representing the number of kilometers to walk as associated data.Finally, you're ready to rate your partner's ideas. This is how you feel about your partner's idea:
Implement a function named rateActivity that takes an Activity value and returns the Approval based on the above sentiments:
rateActivity (Restaurant Turkish)
// => Maybe
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