#### 16.4.1.2 Integer Sequence Operator ‘`:`’

The syntax `first`:`last`:`step`

yields a row
vector of consecutive integers from `first` to `last` counting
by `step`. The final `:``step`

is optional and
defaults to 1 when omitted.

Each of `first`, `last`, and `step` must be a scalar and
should be an integer (any fractional part is discarded). Because
‘`:`’ has a high precedence, operands other than numeric literals
must usually be parenthesized.

When `step` is positive (or omitted) and `end` <
`start`, or if `step` is negative and `end` >
`start`, then the result is an empty matrix. If `step` is 0,
then PSPP reports an error.

Here are some examples:

`1:6` | ⇒ | `{1, 2, 3, 4, 5, 6}` |

`1:6:2` | ⇒ | `{1, 3, 5}` |

`-1:-5:-1` | ⇒ | `{-1, -2, -3, -4, -5}` |

`-1:-5` | ⇒ | `{}` |

`2:1:0` | ⇒ | (error) |