Guarded Methods in OCaml

4 hours ago

Guarded methods attach constraints to the receiver only for specific methods, allowing calls only when the receiver satisfies those constraints.
OCaml does not natively support guarded methods, but they can be encoded using a type equality witness.
The problem arises when a class-level generic constraint is too broad; method-level constraints are more flexible.
Three approaches exist: moving the method outside the class, extension methods, and guarded methods, with the last being most ideological.
The encoding uses a custom eq type with Refl constructor to represent type equalities.
For example, a flatten method on a list of lists requires a witness ('a, 'b list) eq.
A sum method can be constrained to int using ('a, int) eq.
Applying a guarded method with an incompatible type results in a compile-time error, ensuring type safety.
While the encoding is verbose, it demonstrates a practical use of equality witnesses and preserves message-passing semantics.

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Provides a separate import `stableref/react` with stricter hook signatures that fail at the dependency list when stability is not proven, rather than falling back to permissive types.
React guarantees stability for state, setState, and ref objects; these are automatically branded as `Stable`.

The article describes a Haskell technique for creating type-checked non-empty strings using RequiredTypeArguments from GHC 9.10.
It presents a type-level validation mechanism that replaces TemplateHaskell calls, leading to a ~10% build-time improvement in a data-heavy package.
The technique uses a type family or typeclass to enforce non-empty strings at compile time, with custom error messages for invalid inputs.

Lean uses `:=` for definitions and `=` for comparisons, with type inference for `String`, `Nat`, `Int`.
`#eval` runs code and displays results in the InfoView, while `#print` can output to terminal.
Proofs are written with `theorem` and tactics like `unfold`, `decide`, `simp`, and `omega`.

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A hierarchical heap representation is used, where each type (e.g., Array, String) is assigned a range of integers based on pre-order and post-order tree traversal, enabling quick overlap checks.
The alias check uses range overlap: if two objects' types have overlapping ranges, they may alias; otherwise, they do not. Defaulting to 'Any' when type info is absent.

Introduces a phantom brand type `Stable<T>` to encode referential stability into TypeScript types, preventing accidental re-creation of objects, arrays, and functions.
Provides a separate import `stableref/react` with stricter hook signatures that fail at the dependency list when stability is not proven, rather than falling back to permissive types.
React guarantees stability for state, setState, and ref objects; these are automatically branded as `Stable`.

The article describes a Haskell technique for creating type-checked non-empty strings using RequiredTypeArguments from GHC 9.10.
It presents a type-level validation mechanism that replaces TemplateHaskell calls, leading to a ~10% build-time improvement in a data-heavy package.
The technique uses a type family or typeclass to enforce non-empty strings at compile time, with custom error messages for invalid inputs.

Lean uses `:=` for definitions and `=` for comparisons, with type inference for `String`, `Nat`, `Int`.
`#eval` runs code and displays results in the InfoView, while `#print` can output to terminal.
Proofs are written with `theorem` and tactics like `unfold`, `decide`, `simp`, and `omega`.

The article extends the toy optimizer with type-based alias analysis (TBAA) to improve load-store forwarding by distinguishing memory accesses based on object types.
A hierarchical heap representation is used, where each type (e.g., Array, String) is assigned a range of integers based on pre-order and post-order tree traversal, enabling quick overlap checks.
The alias check uses range overlap: if two objects' types have overlapping ranges, they may alias; otherwise, they do not. Defaulting to 'Any' when type info is absent.

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