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Checked functions, not checked arguments

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ajeffrey@roblox.com 2023-09-14 16:14:18 -05:00
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rfcs/new-nonstrict.md
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@ -248,26 +248,26 @@ type of `math.abs`:
This might be better presented as an annotation on the argument type, something like: This might be better presented as an annotation on the argument type, something like:
``` ```
(@checked number) -> number @checked (number) -> number
``` ```
The type The type
``` ```
(S1,...,SM, @checked T, U1...UN) -> V @checked (S1,...,SN) -> T
``` ```
is shorthand for is equivalent to
``` ```
(S1,...,SM, T, U1...UN) -> V (S1,...,SN) -> T
& (unknown^M, ~T, unknown^N) -> error & (~S1, unknown^N-1) -> error
& (unknown, ~S2, unknown^N-2) -> error
...
& (unknown^N-1, SN) -> error
``` ```
Here, `T` is a testable type, that is a scalar type, singleton type,
`table` or `function` (or a union or intersection of testable types).
As a further extension, we might allow users to explicitly provide `@checked` type annotations. As a further extension, we might allow users to explicitly provide `@checked` type annotations.
Checked functions are known as strong functions in Elixir. Checked functions are known as strong functions in Elixir.
@ -288,6 +288,9 @@ solution. It is similar to this design, except that it only works in
`(S)->T` is the equivalent of our `(S)->T` is the equivalent of our
`(~S)->error & (unknown)->(T|error)`. `(~S)->error & (unknown)->(T|error)`.
We could put the `@checked` annotation on individual function argments
rather than the function type.
We could use this design to infer checked functions. In function We could use this design to infer checked functions. In function
`f(x1, ..., xN) B end`, we could generate the context `f(x1, ..., xN) B end`, we could generate the context
`(x1 : T1, ..., xN : TN)` for `B`, and add an overload `(x1 : T1, ..., xN : TN)` for `B`, and add an overload
@ -312,7 +315,7 @@ We would infer type
which is the same as which is the same as
``` ```
(@checked number, @checked string) -> () @checked (number, string) -> ()
``` ```
The problem with doing this is what to do about recursive functions. The problem with doing this is what to do about recursive functions.