Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!swrinde!zaphod.mps.ohio-state.edu!usc!elroy.jpl.nasa.gov!jpl-devvax!lwall
From: lwall@jpl-devvax.JPL.NASA.GOV (Larry Wall)
Newsgroups: comp.lang.perl
Subject: Re: subroutine inspecting its calling environment
Message-ID: <7283@jpl-devvax.JPL.NASA.GOV>
Date: 6 Mar 90 01:57:15 GMT
References: <JBW.90Mar5185907@bucsf.bu.edu>
Reply-To: lwall@jpl-devvax.JPL.NASA.GOV (Larry Wall)
Organization: Jet Propulsion Laboratory, Pasadena, CA
Lines: 31

In article <JBW.90Mar5185907@bucsf.bu.edu> jbw@bucsf.bu.edu (Joe Wells) writes:
: Some questions for the great perl gods:
: 
: 1.  Can a subroutine tell whether it was invoked without arguments?
: 
:     example:  &subroutine_name;

Not that I know of.

: 2.  Can a subroutine tell whether it was invoked in an array or scalar
: context?

Yes, that's what the wantarray operator tells you.

: A boolean scalar context?

No such animal in Perl.

: 3.  Can a subroutine tell whether its invocation was part of an expression
: or was the entire expression?
: 
:     example:  &sub($x);
: 	      $x = (&sub ($x) + &sub2 ($y));

No.  And you can't even tell that the value of &sub($x) above is
unwanted without more context, since the last expression in a block might
return it's value to the outside of the block.

So, no, you can't cheat much...   :-)

Larry