When I define a function inside another function, I get a 'bad placement define' error

Here is my code:

 (require 'hash-table)

 (define (hash-table-get htable key)
    ((hash-inquirer equal?) htable key))

 (define (hash-table-add! htable key val)
    ((ha开发者_StackOverflow社区sh-associator equal?) htable key val))

 (define (hash-table-remove! htable key)
    ((hash-remover equal?) htable key))


 (define (find-max-chain)
      (define table (make-hash-table 1000)) ; works
      .
      .
      .          ; proven working code

      (define (get-chain number) (let ((chain (hash-table-get table number))) chain))

      .
      .
      .        ; more code




    max-entry)
   (find-max-chain)

The problem is the (define (get-chain number) [...] )) part. When I define it and table outside of (find-max-chain) in the global context, It suceeds when I run it. But when I define (get-chain) inside of (find-max-chain) where I need it, when I execute (find-max-chain) I get this error from SCM:

;ERROR: "problem14-new.scm": bad placement define
; in expression: (define (get-chain! number) (let ((chain (hash-table-ge ...
; in scope:
;   (update-max! table max-chain max-entry . #@define)
;   ()  procedure find-max-chain
; defined by load: "problem14-new.scm"

;STACK TRACE
1; (#@define ((update-max! (#@lambda (entry chain) (cond ((> chai ...
2; (#@find-max-chain)
3; (#@define ((hss (#@has-suffix? #@file (#@scheme-file-suffix))) ...

Why is this?

---

Inside a function, defines are only allowed at the beginning of a function (or function-like body), where in any case they are equivalent to a letrec. See this section from R5RS.

---

I'm not very familar with SCM and its error messages, but my first guess would be that you're running afoul of the letrec vs letrec* issue. R5RS says (roughly) that it must be possible to evaluate every right-hand side in a letrec form without touching any of the letrec bound variables; and the same restriction holds for internal definitions. (IIRC, R6RS added a letrec* form that allows such references.)

For example, the following is illegal:

(let ()
  (define x 1)
  (define y (+ 1 x))
  y)

because evaluating the y rhs requires the value of x. In contrast, this is okay:

(let ()
  (define x 1)
  (define f (lambda () (+ 1 x)))
  (f))

That is, it's not a question of scoping, it's a question of when a variable is "ready to use."