[gambit-list] invisible garbage characters from DrScheme Help Desk

Bill Richter richter at math.northwestern.edu
Mon Jan 10 19:36:03 EST 2005

Marc, I figured out what caused my DrScheme/Emacs problem: pasting in
from a DrScheme help window.  So I have 2 suggestions:

1) Get gambit.el to alert folks to invisible garbage characters.

2) Port the DrScheme utilities in list.ss & etc.ss.  Very useful
functions, and I'm sure you could code up very fast versions.

How to replicate my DrScheme/Emacs fiasco:

drscheme &	 ;; version 208

Click "Help Desk" from Help menu

Find docs for: memf


PLT MzLib: Libraries Manual
(memf f l) in "list.ss: List Utilities"

PLT MzLib: Libraries Manual
(memf f l) in "list.ss: List Utilities"

Paste this text into an Emacs window:

 (memf f l)      PROCEDURE 

 Applies f to each element of l (from left to right) until f returns a
 true value for some element, in which case the tail of l starting
 with that element is returned. If f does not return a true value for
 any element of l, #f is returned. 

Now I have invisible garbage characters to puzzle gsi with.  I'm in
trouble if I turn this garbage into a define: (define (memf f l) ...)
The memf line looks like

(memf\hat{A} f l) \hat{A}\hat{A}\hat{A}\hat{A}\hat{A} PROCEDURE 

when I view it with M-x find-file-literally in Emacs.  

Query-replacing and C-x Esc-Esc (repeat-complex-command) tells me that
\hat{A} is \302.  

But it's worse than that, because there's bogus SPC's on the line that
are invisible even with M-x find-file-literally.   I only noticed they
were there because I had a "1" in the far left mode line, which is the
tipoff for coding systems.  
Query-replacing these \302s away leaves the top line looking like

(memf f l)      PROCEDURE 

But there are only 2 honest SPC's on this line.  M-x
find-file-literally, Query-replace and  C-x Esc-Esc tell me the bogus
space is \240:
(query-replace "\240" " " nil nil nil)

Now I'm fine!  Apologies to Neil vD: it wasn't quack.el's fault :) I
suppose I shouldn't expect sympathy when I was too lazy to type
(define (memf f l) ...) & pasted it in.  A tipoff of the invisible
garbage characters is that the words memf, f & l have different colors
in the Help Desk window.  Sorry for double-posting my earlier post.

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