under perl 5.12.2, with deparse, I see constants that are not being optimized. There is also an issue with "if(func)" vs "if(func())".

No parentheses, with module. this works.

BEGIN {
     package mod;
     $VERSION = 1;
     package main;
}

BEGIN {
     if (scalar(%mod::)
         && $mod::VERSION
         ) {eval " sub haveMod () { return 1; }"
            ;}
     else {eval "sub haveMod () { return 0; }"
           ;}
     sub checkMod () {
          if(haveMod)
          {return "goodMod";}
          else {return "badMod";}
     }
}
print checkMod;
[download]

C:\Documents and Settings\Owner\Desktop>perl -MO=Deparse,  consttest.p
+l & perl c
onsttest.pl
BEGIN { $^W = 1; }
sub BEGIN {
    package mod;
    $VERSION = 1;
}
sub BEGIN {
    if (scalar %mod:: and $mod::VERSION) {
        eval ' sub haveMod () { return 1; }';
    }
    else {
        eval 'sub haveMod () { return 0; }';
    }
}
sub checkMod () {
    do {
        return 'goodMod'
    };
}
print checkMod;
consttest.pl syntax OK
goodMod
C:\Documents and Settings\Owner\Desktop>
[download]

No module, no parentheses. This totally doesn't work. I got goodMod instead of badMod.

#!/usr/bin/perl -w
#COMMENTED OUT
#BEGIN {
#     package mod;
#     $VERSION = 1;
#     package main;
#}

BEGIN {
     if (scalar(%mod::)
         && $mod::VERSION
         ) {
          eval " sub haveMod () { return 1; }"
            ;}
     else {
          eval "sub haveMod () { return 0; }"
           ;}
     sub checkMod () {
          if(haveMod)
          {return "goodMod";}
          else {return "badMod";}
     }
}
print checkMod;
[download]

C:\Documents and Settings\Owner\Desktop>perl -MO=Deparse,  consttest.p
+l & perl c
onsttest.pl
BEGIN { $^W = 1; }
sub BEGIN {
    if (scalar %{'mod::'} and $mod::VERSION) {
        eval ' sub haveMod () { return 1; }';
    }
    else {
        eval 'sub haveMod () { return 0; }';
    }
}
sub checkMod () {
    do {
        return 'goodMod'
    };
}
print checkMod;
consttest.pl syntax OK
goodMod
C:\Documents and Settings\Owner\Desktop>
[download]

With parentheses, with module. This works, but didn't optimize.

#!/usr/bin/perl -w
BEGIN {
     package mod;
     $VERSION = 1;
     package main;
}

BEGIN {
     if (scalar(%mod::)
         && $mod::VERSION
         ) {
          eval " sub haveMod () { return 1; }"
            ;}
     else {
          eval "sub haveMod () { return 0; }"
           ;}
     sub checkMod () {
          #NOTE THE PARENTHESES
          if(haveMod())
          {return "goodMod";}
          else {return "badMod";}
     }
}
print checkMod;
[download]

C:\Documents and Settings\Owner\Desktop>perl -MO=Deparse,  consttest.p
+l & perl c
onsttest.pl
BEGIN { $^W = 1; }
sub BEGIN {
    package mod;
    $VERSION = 1;
}
sub BEGIN {
    if (scalar %mod:: and $mod::VERSION) {
        eval ' sub haveMod () { return 1; }';
    }
    else {
        eval 'sub haveMod () { return 0; }';
    }
}
sub checkMod () {
    if (haveMod) {
        return 'goodMod';
    }
    else {
        return 'badMod';
    }
}
print checkMod;
consttest.pl syntax OK
goodMod
C:\Documents and Settings\Owner\Desktop>
[download]

With parenthesis, no module, this works didn't optimize.

C:\Documents and Settings\Owner\Desktop>cat consttest.pl & echo: & ech
+o: & echo:
 & perl -MO=Deparse,  consttest.pl & perl consttest.pl
#!/usr/bin/perl -w
#BEGIN {
#     package mod;
#     $VERSION = 1;
#     package main;
#}

BEGIN {
     if (scalar(%mod::)
         && $mod::VERSION
         ) {
          eval " sub haveMod () { return 1; }"
            ;}
     else {
          eval "sub haveMod () { return 0; }"
           ;}
     sub checkMod () {
          if(haveMod())
          {return "goodMod";}
          else {return "badMod";}
     }
}
print checkMod;


BEGIN { $^W = 1; }
sub BEGIN {
    if (scalar %{'mod::'} and $mod::VERSION) {
        eval ' sub haveMod () { return 1; }';
    }
    else {
        eval 'sub haveMod () { return 0; }';
    }
}
sub checkMod () {
    if (haveMod) {
        return 'goodMod';
    }
    else {
        return 'badMod';
    }
}
print checkMod;
consttest.pl syntax OK
badMod
C:\Documents and Settings\Owner\Desktop>
[download]

A not, no parenthesis, wrong result.

C:\Documents and Settings\Owner\Desktop>cat consttest.pl & echo: & ech
+o: & echo:
 & perl -MO=Deparse,  consttest.pl & perl consttest.pl
#!/usr/bin/perl -w
#BEGIN {
#     package mod;
#     $VERSION = 1;
#     package main;
#}

BEGIN {
     if (scalar(%mod::)
         && $mod::VERSION
         ) {
          eval " sub haveMod () { return 1; }"
            ;}
     else {
          eval "sub haveMod () { return 0; }"
           ;}
     sub checkMod () {
          if(! haveMod)
          {return "badMod";}
          else {return "goodMod";}
     }
}
print checkMod;


BEGIN { $^W = 1; }
sub BEGIN {
    if (scalar %{'mod::'} and $mod::VERSION) {
        eval ' sub haveMod () { return 1; }';
    }
    else {
        eval 'sub haveMod () { return 0; }';
    }
}
sub checkMod () {
    if (not 'haveMod') {
        return 'badMod';
    }
    else {
        return 'goodMod';
    }
}
print checkMod;
consttest.pl syntax OK
goodMod
C:\Documents and Settings\Owner\Desktop>
[download]

So how do you do compile time constant folding with perl? Conditionally eval large complicated subroutines such as checkMod() in my example? And why does "if(func)" seem to check if the function is defined, and optimizes, rather than run it?

---

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