Re: Generators in PHP

On Wed, Aug 8, 2012 at 10:27 PM, Andrew Faulds <ajf@ajf.me> wrote: > Hi Nikita, > > I notice you require brackets round yield $k => $v and yield $v. Is this the > formal syntax, i.e. '(' T_YIELD var => var ')'? If so it makes sense in > a > way, but it feels a little hackish. Does yield $v cause some sort of parsing > issue that putting it in brackets solves? I realise that it's less > ambiguous, but I don't like the idea of it. PHP's syntax has enough special > cases already IMO. Without parenthesis their behavior in array definitions and nested yields is ambigous: array(yield $key => $value) // can be either array((yield $key) => $value) // or array((yield $key => $value)) yield yield $key => $value; // can be either yield (yield $key) => $value; // or yield (yield $key => $value); Apart from that particular case there is the general operator precedence inclarity, e.g. yield $foo . $bar; // could be (yield $foo) . $bar; // or yield ($foo . $bar); This obviously is not a problem per-se, but with yield-style unary operators the precedence rules are often hard to figure out. E.g. most people would probably think that if (include('foo.php') == true) { ... } would be check the return value of include, but it's actually not. Rather it includes the file ('foo.php') == true, which is ''. Another issue was a purely implementational: In order to support by-ref yielding I have to distinguish between variable and non-variable expressions, which breaks the usual precedence rules. I was not able to fix the shift/reduce conflicts that are created by this without requiring the parenthesis. Also I'd like to mention that Python also has the paren-requirement for yield-expressions. It even requires parens for a simple yield, i.e. you'd have to write "data = (yield)". This is not necessary in PHP, because PHP has semicolons. Nikita