Re: [PHP-LANG] Re: [PHP-DEV] Re: [PHP-LANG] Approaching the First Draft [of a language spec]

[..]
> I mean, in my little example, there is additional information in the
> explanation that I don't know how to describe using BNF.  I mean, how
> would you describe this:
>
>    while(bool) expr1; expr2;
>
> vs.
>
>    while(bool): expr1; expr2; endwhile;
>
> In the first case expr2 is not executed within the loop and in the second
> case it is.  There probably is some way to indicate in the BNF that the :
> syntax implies statement grouping, but chances are it would be easy for
> someone to misinterpret that and having a little note that goes along with
> the BNF that clarifies this with an example is not just catering to the
> end user, it is also for the compiler weenie.  We are all end users when
> it comes down to it and something can never be made too clear.

    Well, that is something which can be expressed in a syntactic
    rule. I'm not familiar with writing BNF (only reading), so
    here is the relevant part of the spec in the php-lang module
    (note the difference between statement and statement-list):

iteration-statement:
    'while' '(' expression ')' while-statement

while-statement:
    statement
    ':' statement-list 'endwhile' ';'

statement-list:
    statement
    statement-list statement

    There are examples of what you cannot express in those rules.
    For example, our syntax has to allow constructs like

        $var();

    The validness of such a construct depends on the contents of
    $var, only to be determined at run-time.

    In all cases, semantics definitions have to describe the
    conditions of an action, the action itself and all possible
    results of that action.

    - Sascha