Improve some printouts.

Specifically the one from ,rr.  Also make ,switch syntax error more
friendly.  Also, test for the recent xrepl fix, including its printout.

collects/tests/xrepl/xrepl.rkt

@@ -188,5 +188,18 @@
   json/main> «,sh echo $F»
   @|collects|/json/main.rkt
   json/main> «,top»
+  -> «(display-to-file "#lang racket\n(provide x)\n(define x 1)\n"
+                       "xrepl-test.rkt" #:exists 'truncate)»
+  -> «,rr "xrepl-test.rkt"»             ⇒ first load
+  ; requiring "xrepl-test.rkt"
+  -> «x»
+  1
+  -> «(display-to-file "#lang racket\n(provide x)\n(define x 2)\n"
+                       "xrepl-test.rkt" #:exists 'truncate)»
+  -> «,rr xrepl-test.rkt»
+  ; reloading "xrepl-test.rkt"
+  -> «,rm xrepl-test.rkt»
+  -> «x»
+  2
   -> «,ex»
   @||})

collects/xrepl/xrepl.rkt

@@ -110,15 +110,18 @@
              [best (if (< (string-length best) (string-length x)) best x)])
         best)))
   (define (get-prefix* path)
-    (define x (path->string path))
+    (define x (if (string? path) path (path->string path)))
     (define y (->relname path))
     (if (equal? x y)
       (format "~s" (choose-path x))
       (regexp-replace #rx"[.]rkt$" y "")))
-  (match mod
-    [(? symbol?) (symbol->string mod)]
-    [(list 'quote (? symbol? s)) (format "'~a" s)]
-    [_ (get-prefix* mod)]))
+  (let loop ([mod mod])
+    (match mod
+      [(? symbol?)                 (symbol->string mod)]
+      [(list 'quote (? symbol? s)) (format "'~a" (loop s))]
+      [(list 'file (? string? s))  (loop (string->path s))]
+      [(or (? path?) (? string?))  (get-prefix* mod)]
+      [_ (error 'xrepl "internal error; ~v" mod)])))
 
 (define (here-source) ; returns a path, a symbol, or #f (= not in a module)
   (variable-reference->module-source
@@ -749,14 +752,15 @@
     (for ([mod (in-list last-rr-modules)])
       (define resolved ((current-module-name-resolver) mod #f #f #f))
       (define path     (resolved-module-path-name resolved))
+      (define disp     (module-displayable-name mod))
       (if (hash-ref rr-modules resolved #f)
         ;; reload
-        (begin (printf "; reloading ~a\n" path)
+        (begin (printf "; reloading ~a\n" disp)
                (parameterize ([current-module-declare-name resolved])
                  (load/use-compiled path)))
         ;; require
         (begin (hash-set! rr-modules resolved #t)
-               (printf "; requiring ~a\n" path)
+               (printf "; requiring ~a\n" disp)
                ;; (namespace-require mod)
                (eval #`(require #,mod)))))))
 
@@ -1063,7 +1067,7 @@
       (current-namespace-name name)
       (current-namespace (car (hash-ref namespaces name)))))
   (define (syntax-error)
-    (cmderror "syntax error, see ,help switch-namespace"))
+    (cmderror "syntax error, see \",help ~s\"" (current-command)))
   (match (getarg 'sexpr 'list)
     [(list) (cmderror "what do you want to do?")]
     [(list '?)           (list-namespaces)]