Hi all, I'm a mathematician delving into type theory and proof assistants and with special interests in Racket.
I'm now trying to understand and implement P. Ragde's Proust <https://arxiv.org/abs/1611.09473> "nano proof assistant" and work through the examples in his article. However, I'm pretty much a beginner in Racket and I'm getting some errors. Particularly in the type-infer function, that's also used in the type-check function. Here is the code in the article: (define (type-check ctx expr type) (match expr [(Lam x t) ; lambda expression (match type [(Arrow tt tw) (type-check (cons `(,x ,tt) ctx) t tw)] ; arrow type [else (cannot-check ctx expr type)])] [else (if (equal? (type-infer ctx expr) type) true (cannot-check ctx expr type))])) (define (type-infer ctx expr) (match expr [(Lam _ _) (cannot-infer ctx expr)] [(Ann e t) (type-check ctx e t) t] [(App f a) ; function application (define tf (type-infer ctx f)) (match tf [(Arrow tt tw) #:when (type-check ctx a tt) tw] [else (cannot-infer ctx expr)])] [(? symbol? x) (cond [(assoc x ctx) => second] [else (cannot-infer ctx expr)])])) The first question I have is: what's the (Ann e t) supposed to mean, because I'm getting a syntax error? Is it a type annotation? If so, shouldn't everything be inside the #lang typed/racket module and type annotations everywhere? Secondly, the functions don't seem to work like this, as I'm getting failed matches for everything that's not a lambda expression. Can you please help me clarify the code there or maybe it's already available somewhere? Because just typing in the examples in the article simply doesn't work. I can understand what they are supposed to do, but I lack the skills to fix things myself. Thank you! -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/racket-users/6bdfed6a-13c7-4e86-8dcf-5d61b18e15d7%40googlegroups.com.