Re: status of PL/I as a viable language

["Shmuel (Seymour J.) Metz" <spamtrap@library.lspace.org.invalid>]

In
<819A9E0CA1094B88.6E582670555DCA33.F06C4B2BCD076570@lp.airnews.net>,
on 02/20/2003
   at 05:30 PM, "John R. Strohm" <strohm@airmail.net> said:

>On just about every machine I've ever dealt with, dereferencing a
>null pointer throws a hardware trap. 

If the compiler takes the easy route and represents a null pointer as
0, there won't be a hardware trap on, e.g., a system running MVS[1] or
VM[2].

>Catching a hardware trap and recovering from it is almost always
>MUCH more expensive than checking a pointer for null. 

Why do you care? Explicitly testing is always much more expensive when
the pointer is valid, which is much more common, so in aggregate it is
more expensive than using an invalid address for null and letting the
hardware catch it. Your argument only holds water if the path for
handling an exception is itself time critical.

[1] Of any vintage from OS/VS2 R2 through z/OS.

[2] Of any vintage from VMF/370 through z/VM.

-- 
     Shmuel (Seymour J.) Metz, SysProg and JOAT

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