Or Patterns, Ranges and Guards

Days of the week, number parity and booleans with or-pattern.

// Feature: Or-patterns — multiple alternatives in one arm
// Syntax: `pat1 | pat2 | pat3 => body`
// When to use: group several inputs that trigger the same action,
// without repeating the body.

let day = "Saturday"
let kind = match day {
  "Monday" | "Tuesday" | "Wednesday" | "Thursday" | "Friday" => "weekday",
  "Saturday" | "Sunday" => "weekend",
  _ => "unknown",
}
print(kind)  // weekend

// Numeric.
let n = 5
let parity_or_special = match n {
  0 => "zero",
  1 | 3 | 5 | 7 | 9 => "small odd",
  2 | 4 | 6 | 8 => "small even",
  _ => "large",
}
print(parity_or_special)  // small odd

// Or-patterns with bool.
let flag = false
let label = match flag {
  true | false => "any",
}
// exhaustive in a single line
print(label)  // any
// expected:
// weekend
// small odd
// any

Ranges to classify ages, grades and temperatures.

// Feature: Range patterns — numeric intervals
// Syntax: `start..=end` (inclusive)
// When to use: classify numeric values into ranges instead of
// listing each literal.

let age = 25
let group = match age {
  0..=12 => "child",
  13..=19 => "teenager",
  20..=64 => "adult",
  _ => "senior",
}
print(group)  // adult

// Scores -> letter grades.
let score = 87
let grade = match score {
  90..=100 => "A",
  80..=89 => "B",
  70..=79 => "C",
  60..=69 => "D",
  _ => "F",
}
print(grade)  // B

// Float ranges.
let temp = 22.5
let weather = match temp {
  -100.0..=0.0 => "freezing",
  0.0..=15.0 => "cold",
  15.0..=25.0 => "pleasant",
  25.0..=40.0 => "hot",
  _ => "extreme",
}
print(weather)  // pleasant
// expected:
// adult
// B
// pleasant

Parity, grades with score in the label and a guard combined with or-pattern.

// Feature: Guards — extra `if expr` condition on the arm
// Syntax: `pat if cond => body`
// When to use: refine a pattern with logic that ranges/literals
// can't cover (parity, comparing fields, custom predicates).

let n = 12
let kind = match n {
  x if x < 0 => "negative",
  0 => "zero",
  x if x % 2 == 0 => "positive even",
  _ => "positive odd",
}
print(kind)  // positive even

// Guards with binding.
let score = 75
let grade = match score {
  s if s >= 90 => "A ({s})",
  s if s >= 80 => "B ({s})",
  s if s >= 70 => "C ({s})",
  s => "F ({s})",
}
print(grade)  // C (75)

// Guards combined with or-pattern — guard applies to the whole arm.
let day = "Sunday"
let busy = true
let plan = match day {
  "Saturday" | "Sunday" if busy => "weekend work",
  "Saturday" | "Sunday" => "rest",
  _ => "weekday",
}
print(plan)  // weekend work
// expected:
// positive even
// C (75)
// weekend work