Re^2: last in do vs last in while/for

Ok, but why works the following:

$ perl -le'do { print $i++; last if $i>5 } for (1..10); print "end"'
0
1
2
3
4
5
end
[download]

Comment on Re^2: last in do vs last in while/for Download Code

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Re^3: last in do vs last in while/for by ikegami (Patriarch) on Mar 04, 2009 at 20:01 UTC
Seems that postfix `for` actually creates a loop. I wonder if that has always been the case. `$ perl -MO=Concise,-exec -e'while (foo()) { bar() }' 3 <{> enterloop(next->8 last->d redo->4) v $ perl -MO=Concise,-exec -e'bar() while foo()' $ perl -MO=Concise,-exec -e'do { bar() } while foo()' $ perl -MO=Concise,-exec -e'for (foo()) { bar() }' 8 <{> enteriter(next->d last->g redo->9) lK $ perl -MO=Concise,-exec -e'bar() for foo()' 9 <{> enteriter(next->d last->g redo->a) lK` [download] (Output filtered using `grep 'enterloop\\|enteriter'`) `bar() while foo()` uses a `goto` instead. It is implemented almost identically to: `LOOP_START: ( bar() ), goto LOOP_START if foo();` [download] `do { bar() } while foo()` is not readily representable in Perl, but it doesn't use a loop either. The closest I can get is `LOOP_START: do { bar() }; goto LOOP_START unless foo();` [download] But yes, the answer is "Implementation Details". There's no real reason for it not to work except backwards compatibility.	[reply] [d/l] [select]

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Re^3: last in do vs last in while/for
by ikegami (Patriarch) on Mar 04, 2009 at 20:01 UTC

for

$ perl -MO=Concise,-exec -e'while (foo()) { bar() }'
3  <{> enterloop(next->8 last->d redo->4) v

$ perl -MO=Concise,-exec -e'bar() while foo()'

$ perl -MO=Concise,-exec -e'do { bar() } while foo()'

$ perl -MO=Concise,-exec -e'for (foo()) { bar() }'
8  <{> enteriter(next->d last->g redo->9) lK

$ perl -MO=Concise,-exec -e'bar() for foo()'
9  <{> enteriter(next->d last->g redo->a) lK
[download]

(Output filtered using grep 'enterloop\|enteriter')

bar() while foo() uses a goto instead. It is implemented almost identically to:

LOOP_START:
   ( bar() ), goto LOOP_START if foo();
[download]

do { bar() } while foo() is not readily representable in Perl, but it doesn't use a loop either. The closest I can get is

LOOP_START:
   do { bar() };
   goto LOOP_START unless foo();
[download]

But yes, the answer is "Implementation Details". There's no real reason for it not to work except backwards compatibility.

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