Optional Static Typing (Gradual Types)

Goals

• Preserve SUP’s readability while enabling tooling (errors, IDE, optimization).
• Opt‑in at file/function/variable level; type erasure at runtime unless --typecheck is enabled.

Surface syntax (proposed)

• Type annotations via comment directives on headers:

sup
note types: add(a: number, b: number) -> number
define function called add with a and b
  return add a and b
end function
bye

• Variables (optional): note type: x: number
• Containers: list<number>, map<string, number> (for docs/tooling; enforced by linter/typechecker).

Type system

• Primitives: number, string, bool, null
• Structural containers: list, map
• Functions: (T1, T2, ...) -> R
• Union and optional: A | B, optional<T>

Checker

• Separate tool suptype (future) validates annotations; LSP uses it for diagnostics if configured.
• Gradual: missing annotations default to any and don’t block execution.