Patterns

Patterns take apart sum types and records.

Where	Form
match arm	Variant(x) => e, Variant => e, _ => e
if-let	if (Some(x) = e) { ... } else { ... }
while-let	while (Some(x) = e) { ... }
destructuring binding	Point { x, y } = p;, Some(v) = opt;

• A variant pattern binds the payload to a new name; payload-less variants are written by name.
• Patterns are one level deep: match on the outer variant, then match or read the payload.
• A destructuring binding must be irrefutable: a pattern that could fail to match is a compile-time error.
• Every name a pattern binds is new; it cannot shadow a name in scope.