Path: utzoo!utgpu!water!watmath!clyde!att!rutgers!ucsd!ames!amdcad!sun!pitstop!sundc!seismo!uunet!mcvax!dkuug!freja!stuf From: stuf@freja.dk (Kristoffer H. Holm) Newsgroups: comp.lang.pascal Subject: Re: Re: Comment Pollution Message-ID: <3987@freja.dk> Date: 19 Aug 88 15:30:16 GMT References: <6508@uwmcsd1.UUCP> <840@buengc.BU.EDU> Organization: DIKU, U of Copenhagen, DK Lines: 63 In article <840@buengc.BU.EDU> art@buengc.BU.EDU (A. R. Thompson) writes: >... >we modified an existing compiler. There was a boolean variable spelled >"ttyinuse". Upon reading the code we discovered that when the variable >"ttyinuse" was true the tty was NOT in use! >I'm not arguing in favor of excessive comments. I am however saying that >assigning "meaningful" spellings to identifiers can be very tricky. Why, it should have been named tty_not_in_use (or TtyNotInUse if you prefer that)! In my opinion, properly written Pascal programs only need intensional comments, stating the purpose of chunks of code -- the primary purpose of comments is to allow the reader/maintenance programmer to SKIP code that is irrelevant to him/her! In the example a comment would have done no good (especially not a misleading one)! >... >Er, this is just plain wrong code. From Jensen and Wirth, "Pascal User >Manual and Report" 3rd ed. revised by Mickel and Miner, p. 39: "The >control variable is left undefined upon normal exit from the for >statement." That means that the variable "I" cannot legally be used as it >is in this example as it is undefined when it is used in the test of the >while statement. Not all compilers catch this, though it can be done. Right. While we're at it: variables used as counters in for loops must also be local to the enclosing(program/procedure/function body) of the loop, making "{loop variable in procedure xxxx}" comments dubious. >Try this as a suggested improvement: >const > mincounter=1; > stringsize=whatehaveyou; >type > counterrange=mincounter..stringsize; >var > r:conterrange; >This allows you to change the counter range by changing only the value of >a constant and buys you the advantages of named types. In general I don't agree: you use the wrong principle. Constants and Types shall only be named if they can be misunderstood, or are used in more than one place. And it is OK to have the constants 0 and 1 in ranges. Otherwise you commit a sin similar to over-commenting, and use to many different names. In the above example, type string_index = 1..whatever; var r: stringindex; is more readable---note that "string_index" is a better type name than "counterrange": it shows the intension of the type, not its applications! Of course, "r" should be called something else (not apparent from the example). Regards, Kristoffer. --------------------------------------------------------------------------- Kristoffer H. Holm eunet: stuf@diku.dk Institute of Datalogy (1. sal N), Univ. of Copenhagen, DK-2100 Copenhagen East, DENMARK ---------------------------------------------------------------------------