It is fairly easy to create a let-immutable form yourself
(define-for-syntax (immutable-variable-transformer new-id)
(make-set!-transformer
(λ (stx)
(syntax-case stx (set!)
[(set! x rhs)
(raise-syntax-error #f "cannot mutate immutable variable" stx)]
[(e ...)
(with-syntax ([ap (datum->syntax stx '#%app)])
#'(ap e ...))]
[x new-id]))))
(define-syntax (let-immutable stx)
(syntax-case stx ()
[(_ ([x e] ...) body ...)
#'(let ([x e] ...)
(let-syntax ([x (immutable-variable-transformer #'x)] ...)
body ...))]))
On Sunday, November 5, 2017 at 5:15:24 AM UTC-5, Tony Garnock-Jones wrote:
>
> Would it make sense to have a `let-immutable` form that was just like
> `let` but that forbade use of `set!` with introduced variables?
>
> I'm thinking it could be handy for authors of libraries that introduce a
> lot of bindings in DSLs where mutability has to be strictly controlled.
>
> I think it is probably possible to get the effect of `let-immutable`
> with careful use of identifier macros, but would there be advantages
> internal to the compiler/runtime of being able to up-front, primitively
> declare a set of bindings as immutable?
>
> Tony
>
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