in reply to return value of "if" (documentation?)

AFAIK are if and and opcode-wise identical

lanx@nc10-ubuntu:~$ perl -MO=Deparse -e  ' print if $a '
print $_ if $a;
-e syntax OK
lanx@nc10-ubuntu:~$ perl -MO=Deparse,-p -e  ' print if $a '
($a and print($_));
-e syntax OK

[download]

This and short-circuiting should explain the returned values.

Cheers Rolf

( addicted to the Perl Programming Language)

Replies are listed 'Best First'.
Re^2: return value of "if" (documentation?)
by ikegami (Patriarch) on Jan 08, 2014 at 15:17 UTC

    Deparse tries to reproduce code, while Concise shows what's actually there.

    A more accurate demonstration: 

    $ perl -MO=Concise,-exec -e'print if $a'
1  <0> enter
2  <;> nextstate(main 1 -e:1) v:{
3  <#> gvsv[*a] s
4  <|> and(other->5) vK/1
5      <0> pushmark s
6      <#> gvsv[*_] s
7      <@> print vK
8  <@> leave[1 ref] vKP/REFC
-e syntax OK

$ perl -MO=Concise,-exec -e'$a and print'
1  <0> enter
2  <;> nextstate(main 1 -e:1) v:{
3  <#> gvsv[*a] s
4  <|> and(other->5) vK/1
5      <0> pushmark s
6      <#> gvsv[*_] s
7      <@> print vK
8  <@> leave[1 ref] vKP/REFC
-e syntax OK

    [download]

    But the question is about the if statement. 

    $ perl -MO=Concise,-exec -e'if ($a) { print }'
1  <0> enter
2  <;> nextstate(main 3 -e:1) v:{
3  <#> gvsv[*a] s
4  <|> and(other->5) vK/1
5      <0> pushmark s
6      <#> gvsv[*_] s
7      <@> print vK
8  <@> leave[1 ref] vKP/REFC
-e syntax OK

    [download]
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[d/l]
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      > Deparse tries to reproduce code,

      True but B::Deparse has documented options to switch of the reconstruction of if from and-op. I chose one of the ways¹...

      I also checked it with B::Terse before posting, just wanted to keep the post short.

      Thanks for supporting my point. :)

      > But the question is about the if statement.

      Do you imply that a post-fix if is not a "statement" like pre-fix if ?

      Cheers Rolf

      ( addicted to the Perl Programming Language)

      ¹) 

      -xLEVEL

Expand conventional syntax constructions into equivalent ones that exp
+ose their internal operation. 

...

If LEVEL is at least 7, "if" statements will be translated into
equivalent expressions using "&&", "?:" and "do {}"; for instance

      [download]
      lanx@nc10-ubuntu:~$ perl -MO=Deparse,-x7 -e 'if($a){print $b}'
$a and do {
    print $b
};
-e syntax OK

      [download]

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[d/l]
[select]

        B::Deparse has documented options to switch of the reconstruction of if from and-op. I chose one of the ways¹...

        Maybe I wasn't clear enough: B::Deparse can show they're similar as long as you assume the output is correct. B::Concise can show they're the same, and the output will be correct.

        Do you imply that a post-fix if is not a "statement" like pre-fix if ?

        No. The statement with the post-fix if is not an if statement, but I was not implying it's not a statement. I was implying it's not an if statement.

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