Ranges

Ranges in Kiwi can be used to define a range of integers. Use the to keyword or .. to denote a range.

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As a List

When used inside [ ], a range is immediately evaluated as a List.

Syntax

[ start to end ] [ start .. end ]

Example

println [1 to 5]
# Prints: [1, 2, 3, 4, 5]

# Build a list of numbers from 1 to 10 inclusive, then reverse it.
println [1 to 10][::-1]
# Prints: [10, 9, 8, 7, 6, 5, 4, 3, 2, 1]

r = [20 to 18]
println r
# Prints: [20, 19, 18]

Pitfall — loop bounds that can invert: [a to b] is never empty and never errors when b < a — it just counts down. This is easy to hit by accident in a shrinking loop bound like for i in [0 to n-2] do ... end: as soon as n reaches 1, n-2 is -1, and [0 to -1] silently becomes the 2-element descending list [0, -1] rather than an empty range — the loop body then runs with i = -1, which typically blows up as an out-of-bounds index rather than failing fast at the boundary. If a loop bound is computed and could reach 0 or go negative, guard the loop's entry condition explicitly (e.g. while cond and n > 1 do ...) rather than trusting [0 to n-2] to become empty on its own.

In case when

Ranges can appear directly in when clauses without brackets. The match is O(1) — no list is constructed.

fn describe(n)
  return case n
    when 1..9:   "single digit"
    when 10..99: "double digit"
    else:        "other"
  end
end

println describe(7)    # single digit
println describe(42)   # double digit
println describe(100)  # other

Both .. and to are accepted, bounds are inclusive, and ranges mix freely with literal values in the same case:

fn day_type(d)
  return case d
    when 1..5:  "weekday"
    when 6, 7:  "weekend"
    else:       "invalid"
  end
end

See Control Structures for full details.