[plt-scheme] Small problem with regex-replace*

> I was happy this was a very small program to write, however I wasn't able to 
> create a regexp that only match words,
> so I ended using *dummy* variable to hold the second match that is passed to 
> the scramble procedure. How can I fix this?


Hi Jaime,

The issue is that the regular expression has a group, which we define by 
putting parens in the regexp pattern:

     (let ([word (regexp "([a-zA-Z])+")]) ...)

Here, any matches on our regexp will return two results: one for the whole 
match, and the others for each group in the pattern.

What you probably want is:

     [a-zA-Z]+

which doesn't define a group, so it'll give us a single reported match.


Alternatively, we can look at the documentation on regex patterns:

http://pre.plt-scheme.org/docs/html/mzscheme/mzscheme-Z-H-10.html#node_chap_10

and see the following snippet:

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
Atom     ::= (Regexp)                 Match sub-expression Regexp and
                                       report match
           |  (?:Regexp)               Match sub-expression Regexp 
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;


So there's a way of defining a sub-expression regex without causing match 
to report it.


Let's play with regexp-match just to make this concrete:

;;;;;;
> (regexp-match "[a-zA-Z]+" "hello world")
("hello")
> (regexp-match "([a-zA-Z]+)" "hello world")
("hello" "hello")
> (regexp-match "([a-zA-Z])+" "hello world")
("hello" "o")
> (regexp-match "(?:[a-zA-Z]+)" "hello world")
("hello")
;;;;;;

(The result for "([a-zA-Z])+" surprises me!)


Finaly, the scrambling code might need some clarification.  What happens 
on words with only one letter in them?


Best of wishes to you!