an improved error message for the kind of problem discussed in PR 12093

collects/htdp/convert.rkt

@@ -1,13 +1,24 @@
-#lang scheme/gui
+#lang racket/gui
 
-(require mzlib/etc
-         lang/prim
-         htdp/error)
+;; ---------------------------------------------------------------------------------------------------
+;; functions that demonstrate how one and the same function can be used in three different contexts
+
+(require mzlib/etc lang/prim htdp/error)
 
 (provide-higher-order-primitive convert-gui (f2c))
 (provide-higher-order-primitive convert-repl (f2c))
 (provide-higher-order-primitive convert-file (_ f2c _))
 
+;; ---------------------------------------------------------------------------------------------------
+
+(define OUT-ERROR
+  "The conversion function must produce a number; but it produced ~e")
+
+(define CONVERT-FILE-MESSAGE
+  "It appears as if you created the input file with DrRacket. Please use a different text editor")
+
+;; ---------------------------------------------------------------------------------------------------
+
 (define black-pen  (send the-pen-list find-or-create-pen "BLACK" 2 'solid))
 (define red-brush  (send the-brush-list find-or-create-brush "RED" 'solid))
 (define white-brush  (send the-brush-list find-or-create-brush "WHITE" 'solid))
@@ -89,10 +100,6 @@
       (min-width (+ 4 (inexact->exact w)))
       (min-height (+ 4 (inexact->exact (* 2 h)))))))
 
-;; ------------------------------------------------------------------------
-(define OUT-ERROR
-  "The conversion function must produce a number; but it produced ~e")
-
 ;; ============================================================================
 ;; MODEL
 ;; 2int : num -> int
@@ -222,7 +229,7 @@
              (repl))]
           [else (error 'convert "can't happen")])))))
 
-;; ============================================================================
+;; ---------------------------------------------------------------------------------------------------
 
 ;; make-reader-for-f : (number -> number) -> ( -> void)
 ;; make-reader-for-f creates a function that reads numbers from a file
@@ -231,11 +238,14 @@
 ;;         if any of f's results aren't numbers,
 ;;         the function signals an error
 (define (make-reader-for f)
+  (displayln 'convertfile)
   (local ((define (read-until-eof)
             (let ([in (read)])
               (cond
                 [(eof-object? in) (void)]
-                [(number? in) (begin (check-and-print (f in)) (read-until-eof))]
+                [(number? in) 
+                 (check-and-print (f in))
+                 (read-until-eof)]
                 [else (error 'convert "The input must be a number. Given: ~e\n" in)])))
           (define (check-and-print out)
             (cond
@@ -254,6 +264,11 @@
   (check-arg 'convert-file (string? out) "string" "third" out)
   (when (file-exists? out)
     (delete-file out))
-  (with-output-to-file out
-    (lambda () (with-input-from-file in (make-reader-for f)))))
-;  )
+  (with-handlers ((exn:fail:read?
+                   (lambda (x) 
+                     (define message (exn-message x))
+                     (define reader-exception? (regexp-match "#reader" message))
+                     (if reader-exception?
+                         (error 'convert-file CONVERT-FILE-MESSAGE)
+                         (raise x)))))
+    (with-output-to-file out (lambda () (with-input-from-file in (make-reader-for f))))))

collects/htdp/tests/convert-drracket-error.rkt

@@ -0,0 +1,11 @@
+#lang racket
+
+(require htdp/convert)
+
+(define (Fahrenheit->Celsius x) (* (/ 100 180) (- x 32)))
+
+(with-handlers ((exn? (lambda (x)
+                        (unless (cons? (regexp-match "DrRacket" (exn-message x)))
+                          (error 'test "something went wrong with the test (1)")))))
+  (convert-file "convert-drracket-error.txt" Fahrenheit->Celsius "out.dat")
+  (error 'test "something went wrong with the test (2)"))

collects/htdp/tests/convert-drracket-error.txt

@@ -0,0 +1,5 @@
+;; The first three lines of this file were inserted by DrRacket. They record metadata
+;; about the language level of this file in a form that our tools can easily process.
+#reader(lib "htdp-beginner-reader.ss" "lang")((modname convert-drracket-error) (read-case-sensitive #t) (teachpacks ()) (htdp-settings #(#t constructor repeating-decimal #f #t none #f ())))
+
+214