Add null safety

[synapticvoid]

Design

T? is a built-in first-class optional type — same relationship as E!T to Result[E, T]. It is not sugar over a generic Option[T].

fn find(id: Int) User?
    
let user: User? = find(42)
let name = user orelse "unknown"

Unwrapping

• orelse — provide a default: x orelse fallback
• when — pattern match: when x { value(v) => ..., null => ... }

Rules

• null literal is only valid where a T? type is expected — no untyped null
• T widens to T? automatically (non-null is always a valid optional)
• Assigning T? where T is expected is a type error — must unwrap explicitly

Implementation notes

Mirrors the E!T system:

• PipeTypeAnnotation: add optional: *PipeTypeAnnotation
• PipeType: add optional: *PipeType
• Parser: postfix ? on type annotations; orelse infix expression
• Type checker: enforce null only in optional positions; track unwrap
• Interpreter: Value.null already exists, just needs type gating

Timing

Add after generics are settled — T? being built-in avoids the T? vs Option[T] design knot entirely, same as E!T vs Result[E, T]. Safe to defer as long as no null literal is exposed in the syntax before this lands.