# Set expression¤

The set store unique items, without any particular order. Items in the set must be of the same type. The set is one of basic data structures provided by SP-Lang.

A set is best suited for a testing value for membership rather than retrieving a specific element from a set.

`!SET`

: Set of items¤

Type: *Implicit sequence*, *Mapping*.

Synopsis:

```
!SET
- ...
- ...
```

Hint

Use `!COUNT`

to determine number of items in the set.

There are several ways, how a set can be specified in SP-Lang:

Example

```
!SET
- "One"
- "Two"
- "Three"
- "Four"
- "Five"
```

Example

The mapping form:

```
!SET
with:
- "One"
- "Two"
- "Three"
- "Four"
- "Five"
```

`!IN`

: Membership test¤

Type: *Mapping*.

Synopsis:

```
!IN
what: <item>
where: <set>
```

Check if `item`

is present in the `set`

.

The expression `!IN`

is described in the Comparisons chapter.

Example

```
!IN
what: 3
where:
!SET
with:
- 1
- 2
- 5
- 8
```