Re: Structured exception handling should be a core module.

[Tom Christiansen]

>Now, every error is guaranteed to be an object.  You can call some method 
>or check some attribute of it to find out if it was an exception.  If 
>you're checking a system() or `` failure, you use it in numerical 
>context.  If you're checking a builtin failure, you use it in string 
>context (unless you have some fetish about errno).

It's not a fetish.  It's for portability and reliability.  There is
no guarantee of the precise text that strerror() would produce
when passed EAGAIN or ENOENT, yet it is these errnos by symbolic 
name that the syscalls are defined to return.

Here's a demo:

    bsd%    perl -MErrno=:POSIX -e 'printf "Got: %s\n", $!=ENODEV'
    Got: Operation not supported by device

    redhat% perl -MErrno=:POSIX -e 'printf "Got: %s\n", $!=ENODEV'
    Got: No such device

See the problem?  You *can't* just say 

    if (!syscall(...) && $! =~ /not supported/)

You *must* say

    if (!syscall(...) && $! == ENODEV)

--tom