Unannotated functions were typed by scanning the body, which inferred i32, so falling off
the end emitted `llvm.return 0 : i32` inside a function declared void. The MLIR verifier
rejects that ("expected no operands"), which is what broke Scheduler._yield.
- an unannotated `def` is void in both the forward declare and the body, so the implicit
epilogue emits `ret void`
- translate_return treats a procedure (no annotation, `-> None`, or a void-typed function) as
void: the expression is evaluated for its side effects and `ret void` is emitted. Bare
`return`, `return f()` where f is void, and `return <None value>` are legal and never carry
a value
- body_has_value_return accepts `return f()` and `return <None define>` in a procedure
- `define X = None` is a named None: registered as the string sentinel None, materialized as
a None value at use sites, and exported through the vpi
TermiNexus
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