It automatically balances parentheses for you.
You really have to read the cheat-sheet to appreciate where it helps.
Well, who cares about software to balance brackets when, as the initial post shows, there is no openening bracket to match and close?
I do agree with the fact that paredit is great (as are similar modes for other editors) and that its usage should be strictly enforced, but this is not the issue here.
What is important, though, is that the error message was correct and wasn't cryptic :
(atom? 'h)
*** ERROR IN atom?, "atom.scm"@3.10 -- Wrong number of arguments passed to procedure (not '#<procedure #2 pair?> 'h)
It says "you gave two arguments to procedure NOT, one being the procedure PAIR? and the other being the symbol H"
I believe that what this user now needs help regarding the (human) interpretation of error messages of his implementation. On the other hand (and in other situations) I think it's important to mention that noone would/should consider doing Scheme/Lisp without paredit or anything similar. The fact that it isn't common sense explains why "the others" still think that writing lisp code is a pain because "one has to check every parens one per one."
I would actually even like a paredit-like mode to be by default in the readers of REPLs, when run interactively, so that people who just give a try at a lisp think "Hey, I didn't know it was so cool!"
Cheers.
P!