Re: bin/48843: sh(1): break/continue/return broken inside dot commands

[Richard Hansen <rhansen%bbn.com@localhost>]

On 2014-06-02 13:54, Richard Hansen wrote:
> Note that unlike variable binding, the behavior of dynamic scoping of
> break/continue is a superset of static/lexical scoping (assuming no
> closures):  If the shell does dynamic scoping of break/continue but
> scripts are always written assuming lexical scoping then those scripts
> will still work as expected in all cases.  If POSIX were to specify
> static/lexical scoping then a shell that performs dynamic scoping would
> be conformant but with an extension to the standard.

Oops -- as pointed out in [1] this is incorrect when the argument to
break/continue is greater than the number of lexically enclosing loops.
 An author could write 'break 1000' to make it obvious to other readers
that all loops should be broken.  A script like this might behave
differently on a shell that does dynamic scoping vs. a shell that does
lexical scoping.

So it looks like POSIX will probably have to choose either lexical
(static) or dynamic for the next major version of the standard (Issue 8).

David voiced his preference for lexical [2]; does anyone else have an
opinion?

I think my preference is for dynamic, although I would question the
design decisions of a script author that takes advantage of dynamic
scoping.  Why dynamic over lexical?  Because functionality is lost by
making it lexical:  If a script author wants dynamic but the shell does
lexical, the author is out of luck.  If the shell does dynamic but the
author wants lexical, the author can easily count the number of
lexically enclosing loops and limit the argument of break/continue to
that value.  Dynamic might also be easier to implement.

Thanks,
Richard

[1] http://article.gmane.org/gmane.comp.standards.posix.austin.general/9467
[2] http://article.gmane.org/gmane.os.netbsd.devel.userlevel/17452