This week on www.perl.com, there is a program that needs to perform the following task:

 $_ = <INFO> until !defined($_) || /^(\* Menu:|\037)/;
 return %header if !defined($_) || /^\037/;

[download]
It's reading through a file and it wants to exit the read loop on any of three conditions: At end-of-file; at a line that begins with \037, or at a line that begins with * Menu:. In the first two cases the function should return immediately, but if it sees * Menu: it should continue to the next block of code, which reads and processes the following menu.

I don't really like the code above, because it seems redundant. The two pattern matches are similar but not identical, and the test for defined($_) is repeated. Usually in such cases there's a way to rewrite the block without repetition. I messed around with this a while, but wasn't able to come up with anything I was really happy with.

Here's one possibility: 

while (<INFO>) {
    last if /^\* Menu:/;
    return %header if /^\037/;
}
return %header unless defined $_;

[download]
This avoids the repeated regex, but the defined test is still repeated (although implicitly) and the return is also repeated. I kept wishing there was some way to arrange it so that there was only one return.

Simon Cozens suggested this: 

do { 
   $_ = <INFO>; 
   return %header if /^\037/ || ! defined $_ 
} until /^\* Menu:/ ;

[download]
which is better in some ways, but now you have to assign to $_ explicitly, and also it uses do...until which is an unusual construction.

I keep feeling like there is something obvious I am missing. Does anyone have any other thoughts?

In reply to Control Flow Puzzle by Dominus

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