Find the earlier of two delivery dates, even if one is unknown.

← Operators and Expressions · Ref: Q1208

The <? coalescing minimum operator returns the lesser of two values, handling unset gracefully. Wrap it in a pure function.

  earlierOf() as pure
    -> left as Date, right as Date
    <- rtn as Date: left <? right

If both dates are set, <? returns the earlier one. If one is unset, it returns the set one. If both are unset, the result is unset. This is a COMPARISON operator — it does NOT assign anything.

Do not confuse <? with :=? (guarded assignment). The :=? operator assigns a value only if the target variable is unset — it is not a comparison. See Q1226 for a side-by-side contrast.

See Q1092 for min/max coalescing overview.

Example

defines module qa.operators.coalescemin.dates

  defines function

    earlierOf() as pure
      ->
        left as Date
        right as Date
      <- rtn as Date: left <? right

  defines program

    CoalesceMinDatesDemo()
      stdout <- Stdout()

      // === BOTH DATES SET — returns the earlier ===

      deliveryA <- 2024-11-15
      deliveryB <- 2024-11-08
      earliest <- earlierOf(deliveryA, deliveryB)
      stdout.println(`Earliest delivery: ${earliest}`)

      // === ONE DATE UNSET — returns the set one ===

      confirmedDate <- 2024-12-01
      pendingDate <- Date()
      available <- earlierOf(confirmedDate, pendingDate)
      stdout.println(`Available date: ${available}`)

      // === BOTH DATES UNSET — result is unset ===

      unknownA <- Date()
      unknownB <- Date()
      noDate <- earlierOf(unknownA, unknownB)
      if noDate?
        stdout.println(`Date: ${noDate}`)
      else
        stdout.println("No delivery date available")

      // === INLINE USAGE ===

      shippingDate <- 2024-10-20
      warehouseDate <- 2024-10-25
      pickupDate <- shippingDate <? warehouseDate
      stdout.println(`Pickup by: ${pickupDate}`)

Common mistakes

E50001 — EK9 has no Math.min(); use the '<?' coalescing minimum operator, which also handles unset values. See ek9 -h E50001 for details.

Incorrect:

Math.min(left, right)

Correct:

left <? right

Other ways to ask this

How do I pick the minimum of two optional dates using <? coalescing?
A supplier sends two possible delivery dates but one might be missing — pick the earlier one.
In Java I'd need null checks and compareTo to find the earlier date. What does EK9 offer?
Migrating from Python where I use min(d1, d2) with None checks — what is the EK9 equivalent?

Coming from another language?

Java: d1 == null ? d2 : d2 == null ? d1 : d1.isBefore(d2) ? d1 : d2. Python: min(d for d in [d1, d2] if d is not None). Rust: [d1, d2].iter().flatten().min(). EK9: left <? right — one operator handles all cases.

Keywords: <?, delivery, coalescing, comparison, unset, date, minimum, earlier