Re: 'switch-expression' and the 'type guard' unary operator demo

Hi Kosit, On Sun, 20 Oct 2019 at 16:20, Kosit Supanyo <webdevxp.com@gmail.com> wrote: > You can recognize the difference of those by looking for => > right? But > the parser generator (bison) cannot do that in LR mode (it maybe can in GLR > mode but I'm sure that would be unacceptable due to performance losses/more > memory usage). So workarounds have to be used. I did it by simply return > different tokens from the lexer base on previous token before > switch. >> >> Thanks for clarifying, I thought it might be something like that. > * Different comparisons applied to the same variable/expression, e.g. >> match($user->getScore()) { case <0 => foo(), case >100 => bar(), default >> => baz() } > > > I'd thought about that feature too. But since I also introduced type guard > operator which uses < token it would have parser conflicts > and simple > workarounds cannot apply. > I'm not sure <foo> is the right syntax for type guards, but it's possible we'd want a different syntax for new switch/match functionality anyway. For instance, using a placeholder for the value being tested, like $$ (a common choice in other languages is _, but that's a valid and commonly used function name): match ( $user->getScore() ) { $$ < 0, $$ > 100 => foo(), $$ < 10 => bar(), default => baz() } You could also allow the placeholder in the opening clause to define the same operation for each case: match ( $user->getScore() < $$ ) { 0, default => foo(), 10 => bar(), 100 => baz() } Regards, -- Rowan Tommins [IMSoP]