• Russ Lewis (25/25) Mar 19 2002 Would it make it easier to parse if it didn't allow statements that did
• Walter (4/29) Mar 19 2002 That particular ambiguity is resolved by the rule "if it's parseable as ...

Russ Lewis <spamhole-2001-07-16 deming-os.org> writes:

Would it make it easier to parse if it didn't allow statements that did
nothing?  For example, consider this line of code:
    foo * bar;
If foo is a type, then this is a declaration of a variable called bar,
which is a pointer to foo.  However, if foo and bar are both variables,
then it simply multiplies foo times bar but does nothing with the
result.

Thus, the language cannot be context-free; the compiler needs to know
about the list of declared types and variables in order to know how to
interpret things.  However, if we banned such "do-nothing" statements,
then it would be clear.  Since the expression does not include any
assignment, it is illegal.

Now, there are some obvious problems with this:
    * Function calls.  You must be able to call a function, even if you
don't do anything with the return value, so by necessity no function
call can be considered a "do-nothing"
    * Operator overloading (if ever included in the language)

However, if we get past those two problems, would this really help us?
Maybe there are even more ambiguity problems in the structure of C/C++/D
that we can't really get around...

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"Walter" <walter digitalmars.com> writes:

That particular ambiguity is resolved by the rule "if it's parseable as a
declaration, then it is a declaration."

"Russ Lewis" <spamhole-2001-07-16 deming-os.org> wrote in message
news:3C97CB5B.A27B42F5 deming-os.org...
 Would it make it easier to parse if it didn't allow statements that did
 nothing?  For example, consider this line of code:
     foo * bar;
 If foo is a type, then this is a declaration of a variable called bar,
 which is a pointer to foo.  However, if foo and bar are both variables,
 then it simply multiplies foo times bar but does nothing with the
 result.

 Thus, the language cannot be context-free; the compiler needs to know
 about the list of declared types and variables in order to know how to
 interpret things.  However, if we banned such "do-nothing" statements,
 then it would be clear.  Since the expression does not include any
 assignment, it is illegal.

 Now, there are some obvious problems with this:
     * Function calls.  You must be able to call a function, even if you
 don't do anything with the return value, so by necessity no function
 call can be considered a "do-nothing"
     * Operator overloading (if ever included in the language)

 However, if we get past those two problems, would this really help us?
 Maybe there are even more ambiguity problems in the structure of C/C++/D
 that we can't really get around...

 --
 The Villagers are Online! villagersonline.com

 .[ (the fox.(quick,brown)) jumped.over(the dog.lazy) ]
 .[ (a version.of(English).(precise.more)) is(possible) ]
 ?[ you want.to(help(develop(it))) ]