Conversion functions ​

Conversion functions construct values of specific types. Each function uses the name of the type it produces and starts with a capital letter. For example, Decimal('19.99') creates a Decimal value.

Conversion functions give you explicit control over a value's type where inbound data enters an expression, because inbound data usually arrives as strings. WEL doesn't convert an argument to make a call succeed, except for string interpolation and two configurable Transform data flags. Explicit conversion at the boundary keeps downstream operations type-safe and predictable.

Numbers ​

WEL has three numeric constructors, one for each numeric type.

Integer ​

Converts to an Integer. Accepts an existing Integer or a string of digits.

The conversion is strict. A string that contains anything other than a valid integer raises E102. For example, Integer('3 items') raises an error instead of returning 3.

Integer(value)

Integer('42')

42

Integer(42)

42

Decimal ​

Converts to a Decimal, an exact, arbitrary-precision number.

Use Decimal for money. Pass the value as a string, such as Decimal('19.99'), so the exact digits reach the constructor. Decimal(19.99) converts a Float that's already approximate, which discards the exactness Decimal exists to preserve.

Decimal also preserves scale, so Decimal('12.50') keeps its trailing zero through arithmetic and a total stays a currency amount rather than becoming 12.5.

Decimal(value)

Decimal('19.99')

19.99

Decimal(5)

5

Float ​

Converts to a Float, a binary floating-point number.

Appropriate for measurements, ratios, and scientific values, where approximate precision is acceptable. Not appropriate for money, because a Float can't represent most decimal fractions exactly. Refer to Decimal for exact arithmetic instead.

Float(value)

Float('3.14')

3.14

Text and truth ​

The following constructors convert to String, Bool, and Binary:

String ​

Converts a scalar value to a String, using the data-plane locale.

Rejects Binary and collections. A List or Map is never turned into a string implicitly or by this function. Use to_json or to_wel to serialize a collection deliberately. This restriction exists because a silently stringified collection is one of the hardest transformation bugs to notice downstream.

String(value)

String(42)

42

String(Decimal('19.99'))

19.99

Bool ​

Converts a value to a Boolean. Accepts an existing Boolean, or the strings 'true' and 'false'.

'yes', '1', and 'Y' aren't accepted because their meaning depends on the source system. Map source-specific values to a Boolean explicitly:

if _.flag == 'Y' then true else false

Bool(value)

Bool('true')

true

Binary ​

Converts an ASCII string to Binary bytes.

Use encode_string, which takes an explicit encoding, for text that isn't ASCII. Binary raises E008 on non-ASCII input rather than selecting one.

Binary(value)

Binary('AB')

0x"4142"

Dates and times ​

WEL distinguishes an exact instant from a calendar date or wall-clock time without a time zone. Choosing the correct type helps prevent date shifts across time zones. Refer to Temporal functions for how to work with each type once it's constructed.

DateTime ​

Converts to a DateTime, an exact instant with a time zone.

Use it to record an event happening, such as a creation timestamp, an event time, or an audit record.

DateTime(value)

DateTime('2026-03-15T09:30:00Z')

2026-03-15T09:30:00Z

PlainDate ​

Converts to a PlainDate, a calendar date with no time and no zone.

Use it for a date that is the same everywhere, such as an invoice date, a birth date, or a contract start. A DateTime stored in place of a PlainDate can shift a day when it crosses a zone boundary.

PlainDate(value)

PlainDate('2026-03-15')

2026-03-15

PlainTime ​

Converts to a PlainTime, a time of day with no date and no zone, such as a store opening time.

PlainTime(value)

PlainTime('09:30:00')

09:30:00

PlainDateTime ​

Converts to a PlainDateTime, a date and time with no zone.

PlainDateTime strips the zone from a DateTime argument rather than converting it, so the wall-clock reading is kept as-is.

PlainDateTime(value)

PlainDateTime('2026-03-15T09:30:00')

2026-03-15T09:30:00

Duration ​

Converts to a Duration, a length of time written in ISO 8601 duration form. For example, PT1H30M.

Duration(value)

Duration('PT1H30M')

PT1H30M

Sentinels ​

The following constructors build the two markers WEL uses to represent an absence:

Null ​

Returns null. Takes no arguments.

Null()

Null()

null

Skip ​

Returns the Skip sentinel. It takes no arguments.

Skip omits a field entirely instead of sending null for it. Refer to Null and Skip for the full comparison, including how Skip filters a list inside map_by. Use Skip when a destination distinguishes an explicitly cleared field from an untouched one, which many CRM APIs do.

Skip()

Use case: Convert an inbound payload at the boundary ​

Every field arrives as a string, including ones that logically aren't. Convert them once, at the top, so the rest of the transformation can work in real types:

Input

{
  "id": 1001,
  "qty": "3",
  "total": "149.50",
  "shipped": "true",
  "ship_date": "2026-03-15"
}

Formula

{
  order_id: String(_.id),
  qty: Integer(_.qty),
  total: Decimal(_.total),
  shipped: Bool(_.shipped),
  ship_date: PlainDate(_.ship_date)
}

Output

{
  "order_id": "1001",
  "qty": 3,
  "total": 149.50,
  "shipped": true,
  "ship_date": "2026-03-15"
}

total keeps its trailing zero because Decimal preserves scale. ship_date is a PlainDate, so it can't drift a day when a later step applies a time zone.

Related ​

• Data types: The 16 WEL data types and when to use each one.
• Numeric functions: Round a Decimal.
• Temporal functions: Work with dates after conversion.
• Error codes: Troubleshoot job failures such as E008 and E102.