3 ms·

No, in perl eval explicitly has access to the local scope. This is used for capturing otherwise fatal errors in perl (it can be used similarly to try/catch).

kazinator 10y ago
Wouldn't the handlers for exception handling by dynamically scoped, not lexically? If we have a try block, and call a function, and if that function throws, we want the try block to be able to catch that. The function is not understood as having magic access to an environment; it's a pervasive dynamic environment that is visible to the current execution context at all times, in which exit points for non-local transfers are established. That's almost the entire point since an error situation that is entirely confined to a lexical scope can be dealt with using some local control flow (some form of goto, or structured derivative thereof).
- simcop2387 10y ago
  So with perl 5 there isn't a real exception handler like you'd expect from other languages (I'm unsure of perl 6). It works like the following (program output available at [1]): use v5.24.0; my $x = 1; my $y = "bar"; sub foo { # this sub fails fatally die "what is going on here"; } say "x is $x, y is $y"; # 1 and bar eval { # similar to try my $y = "baz"; # we have a new lexical scope in here too. $x = 2; # but this will change the outside scope since it's also available to us say "x is $x, y is $y"; # 2 and baz foo(); $x = 3; # this never happens }; if ($@) { # check for an error, similar to catch say "CAUGHT ERROR: ", $@; # just parrot the error out for now. } say "x is $x, y is $y"; # 2 and bar Inside the eval the lexical scope outside is still available and a new one is also available. The error that happens gets stuffed into a special variable and you can choose to handle it or not later. This works the same way if you give eval a string to run also. [1] https://perlbot.pl/pastebin/pl5u9w https://perlbot.pl/pastebin/pl5u9w

kazinator 10y ago

Wouldn't the handlers for exception handling by dynamically scoped, not lexically? If we have a try block, and call a function, and if that function throws, we want the try block to be able to catch that. The function is not understood as having magic access to an environment; it's a pervasive dynamic environment that is visible to the current execution context at all times, in which exit points for non-local transfers are established. That's almost the entire point since an error situation that is entirely confined to a lexical scope can be dealt with using some local control flow (some form of goto, or structured derivative thereof).

simcop2387 10y ago
So with perl 5 there isn't a real exception handler like you'd expect from other languages (I'm unsure of perl 6). It works like the following (program output available at [1]): use v5.24.0; my $x = 1; my $y = "bar"; sub foo { # this sub fails fatally die "what is going on here"; } say "x is $x, y is $y"; # 1 and bar eval { # similar to try my $y = "baz"; # we have a new lexical scope in here too. $x = 2; # but this will change the outside scope since it's also available to us say "x is $x, y is $y"; # 2 and baz foo(); $x = 3; # this never happens }; if ($@) { # check for an error, similar to catch say "CAUGHT ERROR: ", $@; # just parrot the error out for now. } say "x is $x, y is $y"; # 2 and bar Inside the eval the lexical scope outside is still available and a new one is also available. The error that happens gets stuffed into a special variable and you can choose to handle it or not later. This works the same way if you give eval a string to run also. [1] https://perlbot.pl/pastebin/pl5u9w https://perlbot.pl/pastebin/pl5u9w