Detecting mismatched parens better

[Alan Bawden <ALAN at MIT-MC>]

I don't like your proposed paren hack:

1)  First off, I find "( eval-when" un-aesthetic.

2)  It makes certain formerly legal printed representations of lisp
objects now generate errors.  I don't like adding the collumn position
of a parenthesis to the syntax of the language as understood by READ.

3)  It doesn't really work reliably.  Consider:

( eval-when (eval compile)
(defun foo ()
  (let ((base 10.)		;missing close paren here
    (print *foobar*))))

(defun bar ()
  ...)

The missing close paren simply causes the rest of the forms in the
file to be treated as if they were inside the eval-when, there is no
way to tell what the user intended in this case.  I would rather have
the compiler read through to the end of the file and get an error,
than have some hack go off when the next

( eval-when ...

is encountered that decides (incorrectly) to supply the close paren
right then and there and procedes with the compilation.

I cannot imagine that I would ever simply allow something like this to
supply close parens for me.  I would certainly be so suspicious of
whatever it had done that I would fix up the paren error in my file
and then recompile the wrole file beyond that error.  Since that is
almost exactly what I would do today in that case, and since today
that syntax error would be found immediately and no additional
compilation would happen, I see no benefit to the mechanism.