# `Feel.Builtin.Conversion`
[🔗](https://github.com/FeeJai/BDM/blob/feel-v0.1.0/apps/feel/lib/feel/builtin/conversion.ex#L1)

The conversion functions of FEEL (DMN 1.6, section 10.3.4.1, Table 73).

They build values of the temporal types, numbers, strings, and ranges from other
values, mostly from text: `date("2020-01-01")`, `number("1.000,5", ".", ",")`,
`string(x)`, `range("[1..5]")`. The temporal constructors read the lexical forms
of XML Schema.

## What is written

All eight: `date`, `time`, `date and time`, `duration`, `years and months duration` and `string` (D-56),
and `number` and `range` (D-73).

| Call | Result |
| ---- | ------ |
| `date(from)` | `from` is a string (`Feel.Value.Date.parse/1`), or the date of a date and time as it is written, whatever its zone; a date is a date and time at UTC midnight (D-56), so its date is itself |
| `date(year, month, day)` | the numbers, with a fraction cut off |
| `time(from)` | a string (`Feel.Value.Time.parse/1`), a time, or the time of a date and time with its zone; a date is a date and time at UTC midnight (D-56, the TCK, 1116 #053) |
| `time(hour, minute, second, offset)` | the offset is a days and time duration in seconds, or `null` for a time with no zone; it can be left out |
| `date and time(from)` | a string (`Feel.Value.DateTime.parse/1`); a date alone is local midnight, and a date and a zone is midnight in the zone (`"2012-03-07Z"`, D-68) |
| `date and time(date, time)` | the date of a date or a date and time, and the time with its zone |
| `date and time(date, time, timezone)` | the same for a time with no zone, which gets the zone `timezone`: `"Z"`, `"+01:00"` or the id of a zone |
| `duration(from)` | a string, of either kind |
| `years and months duration(from, to)` | the whole months between two dates, or dates and times, taken by their dates (see below) |
| `string(from)` | the text of a value (`Feel.Value.Format`); `null` for `null` |
| `number(from)` | a number is itself; a string is a number as a literal is (`-1.5`, `.5`, `1e3`), and nothing else is |
| `number(from, grouping separator, decimal separator)` | the string, with every grouping separator taken out and a decimal comma made a period (see below) |
| `range(from)` | the text of an interval, `[18..21)`, with literal endpoints (`Feel.Runtime.RangeText`) |

A null argument is out of the domain of every function here, and the call is `null` with an
`:argument_out_of_domain` error, but for the offset of `time` (`null` is a time with no zone) and for
`string(null)`, which is `null` and no error (the TCK, 1115 to 1121 and 0079). So is an argument of
the wrong kind, a string that is not a date, time, date and time or duration, and a number out of range.

`number(from, grouping separator, decimal separator)` is the procedure of the footnote of Table 73. The
grouping separator is a space, a comma, a period or `null`, the decimal separator is a period, a comma or
`null`, and they differ unless both are `null`; any other separator, and a `from` that is not a string, is
`null` with an error. Every grouping separator is taken out of `from`, a decimal comma is made a period, and
what is left has to be a number as a literal is. A decimal separator that is `null` leaves the period as it
is, so `number("1,000,000.00", ",", null)` is `1000000.00`. Where the grouping separators stand is not
looked at (`"1,0,0,0"` is 1000), and the scale of the text is kept. The two-argument form does not exist.

The months between two dates are `to - from` in years and months, less one if `to` is before `from` in
the month (`2013-08-24` to `2017-12-15` is 51). The time of day and the zone of a date and time are not
looked at (`2014-12-31T23:59:59` to `2016-12-31T00:00:01` is 24, as the TCK has it), and a date can be
given for either: the date of a date and time is its fields, as written.

# `functions`

```elixir
@spec functions() :: [Feel.Builtin.Function.t()]
```

The functions of this module that are written, as `Feel.Builtin.Function`s.

# `names`

```elixir
@spec names() :: [Feel.Name.t()]
```

Returns the canonical names of the functions of this module, sorted.

    iex> "date and time" in Feel.Builtin.Conversion.names()
    true

---

*Consult [api-reference.md](api-reference.md) for complete listing*