After filtering by Switch, my program becomes what is listed below and the subroutine Switch::case is called with my regexp as parameter. So, my bad, this seems to be a case for unscoped sub instead of unscoped eval. BTW: I am peeking at parrot and is positively impressed.

use Carp;

sub enum {
  my  @enum = split /,/,  $_[0];
  my  $i = 0;
  for ( @enum ) {
    S_W_I_T_C_H: while (1)  { local $::_S_W_I_T_C_H; Switch::switch  (
+$_);
      if (Switch::case  qr/([A-Z]+\d*)(?:\s*=\s*(\d)+)?/i){ while (1) 
+{  
        m/([A-Z]+\d*)(?:\s*=\s*(\d)+)?/i;       
        no strict;
        $i = $2 if defined $2;
        eval "sub $1() { $i }";
        $i++;
    ;last S_W_I_T_C_H } continue { goto C_A_S_E_1 } last S_W_I_T_C_H; 
+C_A_S_E_1: }
      else    { croak qq(bad enum member syntax: "$_") }
    }continue {last}
  } 
}


enum "INFIX, PREFIX=4, SUFFIX" ;

print INFIX(), ":", PREFIX(), ":",  SUFFIX(), "\n";
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