amb-fail not provided

[kisp]

Description

Currently, the sicp module exports amb but not amb-fail, which seems inconsistent. Since amb-fail is an essential part of handling failures in the amb evaluator, it makes sense for it to be exported as well.

Steps to Reproduce

16:13 $ racket
Welcome to Racket v8.15 [cs].
> (require sicp)
> (amb 1 2 3)
1
> amb-fail
amb-fail: undefined;
 cannot reference an identifier before its definition
  in module: top-level
 [,bt for context]
>

This results in an error because amb-fail is not available in the module's public interface.

Proposed Fix

Export amb-fail alongside amb by updating sicp/main.rkt:

16:15 $ git diff
diff --git a/sicp/main.rkt b/sicp/main.rkt
index 5548679..0453050 100644
--- a/sicp/main.rkt
+++ b/sicp/main.rkt
@@ -41,7 +41,7 @@

 (provide amb)

-(define (amb-fail) (error "amb tree exhausted"))
+(define+provide (amb-fail) (error "amb tree exhausted"))
 (define (set-amb-fail! x) (set! amb-fail x))

 (define-syntax-rule (explore +prev-amb-fail +sk alt)

Would love to hear any thoughts on this!