Xref: utzoo comp.lang.misc:1429 comp.lang.pascal:803
Path: utzoo!mnetor!uunet!lll-winken!lll-lcc!pyramid!weitek!rober
From: rober@weitek.UUCP (Don Rober)
Newsgroups: comp.lang.misc,comp.lang.pascal
Subject: Re: Loops
Message-ID: <9158@weitek.UUCP>
Date: 13 Apr 88 05:34:16 GMT
References: <2827@enea.se> <1557@pasteur.Berkeley.Edu> <2773@mmintl.UUCP> <294@tmsoft.UUCP> <11047@shemp.CS.UCLA.EDU>
Reply-To: rober@weitek.UUCP (Don Rober)
Organization: WEITEK Corp. Sunnyvale Ca.
Lines: 20

In article <11047@shemp.CS.UCLA.EDU> gast@lanai.UUCP (David Gast) writes:
>
>While it is commonly believed that it is impossible to change the
>index variable in a for loop, it is possible to do so.  Consider the
>following program.
>
 [illegal program with threatening for loop reference deleted]

While it is a pain, it it not really that difficult to enforce this area of the
Pascal standard. When an assignment to a variable is made, the symbol table is 
marked noting a potentially threatening reference. When the for-loop is seen, 
the variable is checked to see if a threatening reference happened; if so,
an error.  (Appropriate care must be taken for threatening references that 
*follow* the for-loop.)

The Unisys A-series compiler does this checking.

It was interesting to see the number of otherwise "portable" programs that 
would fail with a standard-enforcing compiler.-- 
----------------------------------------------------------------------------
Don Rober				UUCP: {pyramid, cae780}!weitek!rober
Weitek Corporation	1060 East Arques		Sunnyvale, CA 94086