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From: tchrist@convex.COM (Tom Christiansen)
Newsgroups: comp.lang.perl
Subject: Re: Patterns vs Strings
Message-ID: <1991Feb07.210023.8308@convex.com>
Date: 7 Feb 91 21:00:23 GMT
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Reply-To: tchrist@convex.COM (Tom Christiansen)
Organization: CONVEX Software Development, Richardson, TX
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From the keyboard of rbj@uunet.UU.NET (Root Boy Jim):
:Are patterns a semi data type in their own right?
:Are they replacable with strings?
:The manual/book never addresses this explicitly.
:
:My experiments lead me to belive that
:whenever a "pattern" is expected, slashes
:are "promoted" to double quotes, as if "qq"
:had been stuck in front.

A semi-data type?  I'm not sure what a real data type is.  I think by the
most stringent criteria (you can have anonymous temporaries), only atoms,
oops I mean scalars :-), and lists are real data types, and everything
else is just some magic operation you perform on them, like regexp
matching, hashed array lookups, code evals, and indirect function calls
and i/o.  But I don't really tell people that (often).  Usually I consider
anything that you can pass around and has its own name space is a real
data type.

I believe your observations to be correct.  I think Larry once explained that
    if ($a =~ $b)
is legal, and counts as 
    if ($a =~ /$b/)
but it may be somehow less efficient.  Certainly it's fair to use
variables in pattern patching operations.  Various tricks (like //,
/$foo//o, eval, ...) can be used to speed up the operation.

Note that if you use alternate delims on the match, like m#bar#, it still
gets qq// interpolated, unless you should use m'bar', in which case you
get q// action.  I'm not sure I've ever seen this written down in the man
page or the book.  I don't think you can use m`bar` for qx// action, but
neither can I think of why you'd ever want it to.

--tom
--
 "All things are possible, but not all expedient."  (in life, UNIX, and perl)