Unbound variable from mutual reference

[WeixiMa]

Hi Alexis,

I've been playing with this wonderful tool you've made (thank you!) and run into something that is unexpected. I was following the docs to parse "prefix" function calls, like f(x, y). And the code below worked like a charm.

(define num/p (syntax/p (token/p 'NUM)))
(define id/p (syntax/p (token/p 'ID)))
(define prefix/p
  (syntax/p
   (do [f <- id/p]
       (token/p 'LPAREN)
       [xs <- (many/p expr/p #:sep (token/p 'COMMA))]
       (token/p 'RPAREN)
       (pure (prefix f xs)))))

(define expr/p
  (or/p (try/p prefix/p)
        num/p
        id/p))

Then, when I tried to parse infix function calls, like "x + y", however, things became confusing. Here's my code.

(define infix/p
  (syntax/p
   (do [l <- expr/p]
       [f <- id/p]
       [r <- expr/p]
       (pure (infix f l r)))))

(define expr/p
  (or/p (try/p prefix/p)
        (try/p infix/p)
        num/p
        id/p))

It didn't compile and Racket yelled at me:

expr/p: undefined;
 cannot reference an identifier before its definition
  in module: "my-directory/parser.rkt"
Context (plain):
 my-diretory.emacs.d/elpa/racket-mode-20240130.2013/racket/repl.rkt:322:0 configure/require/enter

The infix/p doesn't look very different from the prefix/p, which refers to expr/p as well. I wonder if it's by design or it might be a bug. Thanks a lot!