[timfennis]

Making Any explicit (#331) leaves a cast as the only way to get a value out of Any, and there was no way to test a value's type: x as T stops the program when x isn't a T. x as? T is that test: Some(x), as a T, when the value is a T, and None when it isn't. It has type Option<T>.

let v: Any = 3;
if (v as? Int).is_some() { print("an int"); }
print([1, "a"] as? List<Int>);   // None

• Lexer, parser, formatter, highlighter and LSP completion know as?, which has the precedence of as (so (x as? Int).is_some() needs its parentheses) and needs a space after it, as ? can be part of a name.
• The analyser checks it as it checks as: a cast that can never succeed is an error (it would always be None), and one it can prove needs no check. Unlike as, it doesn't settle what isn't known about the value: testing xs as? List<Int> leaves an empty list free to hold Strings. A number written there still takes the type: 1 as? Float is Some(1.0).
• A new TryCast instruction converts the value as as does, functions included (they get their calls checked), and gives None instead of failing. Its body is out of the VM's main loop, so calls run exactly as before (fib(27) executes the same number of instructions).

The manual's casts page has a section on it.

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[chatgpt-codex-connector]

Codex Review Summary: ✅ Completed

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-11-13T21:14:47.774011Z	f6111db	PR opened

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