Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ncar!ames!oliveb!Ozona!chase
From: chase@Ozona.orc.olivetti.com (David Chase)
Newsgroups: comp.lang.misc
Subject: Re: language commenting constructs
Message-ID: <39273@oliveb.olivetti.com>
Date: 15 Mar 89 01:32:07 GMT
References: <1543@zen.UUCP> <10460@lanl.gov>
Sender: news@oliveb.olivetti.com
Reply-To: chase@Ozona.UUCP (David Chase)
Organization: Olivetti Research Center, Menlo Park, CA
Lines: 78

In article <10460@lanl.gov> jlg@lanl.gov (Jim Giles) writes:
>// Or better yet, I use a language like C++ which
>// always terminates comments beginning with '//'
>// at the end of a line - automatically.
 ...
>It is doubtful that anyone designing a new language would
>consider the old-fashioned C-like syntax to be desireable.

Sigh.  At the risk of sounding like a broken record (not that that
stops anybody else on the net), there were languages before C (hence
older) and they used the     
        // this is a comment to EOL style of comments.  
Specifically, there was BCPL, C's grandparent.  I have often wondered
why some features present in BCPL were removed in C; I construct my
own explanations, but they tend to be unflattering to the designers of
C.  BCPL had its warts, of course, but I often think that they threw
out the baby and kept the bathwater.  Examples of "nice" things
discarded include:

*  // comments

*  VALOF <block> expressions
     For example, here's how to use a "case" statement within
     an expression:

        VALOF SWITCHON x INTO $(
              CASE 'a':
	      CASE 'e':
              CASE 'i':
              CASE 'o':
              CASE 'u':
                   RESULTIS vowel
              CASE 'y':
                   RESULTIS sometimes
              DEFAULT:
                   RESULTIS consonant
              $)
     (This has reappeared within GCC, I believe)

*  extended relational tests (e.g. '0' <= ch <= '9')

*  many fewer parentheses (at the expense of added keywords, but it
   was a lot nicer to read)

*  good generic types (actually, only one type, but it
     includes pointers, integers, procedures, you name it)

*  :=/= instead of =/== 
     This is a matter of taste, but the character-counting
     justifications never made much sense to me, especially since
     BCPL also used = for initialization, allowed elision of
     redundant semicolons, and permitted multiple assignments.
     Thus, 
        int a = 1;
        int b = 2;
        int c = 3;
     would be rendered as
        LET a,b,c = 1,2,3
     If a variable's value were subsequently changed, then := would
     be used. For example,
        a := b + c

*  cleaner syntax for function definitions (VALOF helps here)
     For example,
        LET min2(a,b) = a < b -> a,b
        AND min3(a,b,c) = a < b -> min2(a,c), min2(b,c)
        AND abs(a) = a < 0 -> -a,a
     I just defined three functions; you can all construct their
     C versions and compare.

I have always wondered what caused the designers of C to leave all
this fine stuff out; it's not like the BCPL compiler was a pig, and
few of these features had any real effects on portability or
efficiency (the generic single type is apparently the biggest
headache).  Enquiring minds want to know what the reasoning was behind
the choices made for C.

David