String searching in Rebol or Red

I'm interested in searching on a lot of long strings, to try and hack out a sed-like utility in rebol as a learning exercise. As a baby step I decided to search for a character:

>> STR: "abcdefghijklmopqrz"

>> pos: index? find STR "z"
== 18

>> pos
== 18

Great! Let's search for something else...

>> pos: index? find STR "n"
** Script Error: index? expected series argument of type: series port
** Where: halt-view
** Near: pos: index? find STR "n"

>> pos
== 18

What? :-(

Yeah, there was no "n" in the string I was searching. But what is the benefit of an interpreter blowing up instead of doing something sensible, such as returning a testable "null" char in pos?

I was told I should have done this:

>> if found? find STR "z" [pos: index? find STR "z"]
== 18

>> if found? find STR "n" [pos: index? find STR "n"]
== none

>> pos
== 18

Really? I have to search the string TWICE; the first time just to be sure it is "safe" to search AGAIN?

So I have a three-part question:

1. 
   

   How would a wizard implement my search function? I presume there is a wizardly better way better than this....

   
   


2. 
   

   Is Red going to change this? Ideally I'd think find should return a valid string position or a NULL if it hits end of string (NULL delimited, may I presume?). The NULL is FALSE so that would set up for a really easy if test.

   
   


3. 
   

   What is the most CPU effective way to do a replace once I have a valid index? There appear to so many choices in Rebol (a good thing) that it is possible to get stuck in choosing or stuck in a suboptimal choice.