Path: utzoo!attcan!uunet!lll-winken!lll-tis!helios.ee.lbl.gov!pasteur!ucbvax!VENUS.YCC.YALE.EDU!LEICHTER
From: LEICHTER@VENUS.YCC.YALE.EDU ("Jerry Leichter ", LEICHTER-JERRY@CS.YALE.EDU)
Newsgroups: comp.os.vms
Subject: Re: DCL qualifier parsing
Message-ID: <8805260746.AA19083@ucbvax.Berkeley.EDU>
Date: 24 May 88 15:42:00 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 44


	Harvey Rarback (rarback@bnlux0.UUCP) writes:
	>$ library /extract="2"+"2"       fortune.tlb
	>%DCL-W-PARMDEL, invalid parameter delimiter - check use of special
		characters

	Do:
	$ LIBRARY/EXTRACT="''2+2'"

When did you start running VMS V6.0?  :-)

This doesn't work in any version of VMS I've ever seen, it's actually equiva-
lent to the (rather unlikely) command:

	$ LIBRARY/EXTRACT="+2'"

DCL does not have any syntax for specifying expression evaluation at arbitrary
places in the input.  What it you CAN specify is SUBSTITUTION OF SYMBOLS, a
much more limited thing.  Expression evaluation occurs in certain well-defined
contexts, such as after an "=", ONLY.  The original author's problem can be
solved easily in two statements:

	$ value = "2" + "2"
	$ LIBRARY/EXTRACT="''value'"
(or	$ LIBRARY/EXTRACT=&value)

This is a bizzare example, actually, since I THINK the original author is
expecting to extract module 4 - but he will actually get module 22.  The "+"
is polymorphic; it adds integers, but concatenates strings.  In most cases in
DCL, the two are freely interchangeable, but here the difference is noticable:

	$ value = "2" + "2"	!Two strings, result "22"
	$ value = 2 + 2		!Two integers, result 4
	$ value = "2" + 2	!String coerced to integer, result 4

If it was indeed "22" that the original author wanted, there is a one-line
solution (the point of which is only visible if you use variables):

	$ X1 = "2"
	$ X2 = "2"
	$ LIBRARY/EXTRACT="''X1'''X2'"

Concatenation is an implicit side-effect of substitution, so no evaluation is
needed.
							-- Jerry