$term = '((1 + 2) * (2 -1) + 7 / 5) + (2 * 3) + 5';

printf("TERM  : $term\n");

$term =~ s/\s+//g;
$idx  = 1;

#-----------------------------------------------------------------------------#
sub evalSubTerm {
  my($op1, $op, $op2) = @_;

  if    ( $op eq '*' ) { return($op1 * $op2); }
  elsif ( $op eq '/' ) { return($op1 / $op2); }
  elsif ( $op eq '+' ) { return($op1 + $op2); }
  else                 { return($op1 - $op2); }
}

#-----------------------------------------------------------------------------#
sub resolveOps {
  my($op) = @_;

  for $subTerm ( values(%subTerms) ) {
    while ( ($subTerm =~ s!^(.*?[+-].*?)(T?\d+(?:\.\d*)?${op}T?\d+(?:\.\d*)?)(.*?)$!$1T$idx$3!) ||
            ($subTerm =~ s!^(.*?)(T?\d+(?:\.\d*)?${op}T?\d+(?:\.\d*)?)(.*?[+-].*?)$!$1T$idx$3!) ) {
      $subTerms{"T$idx"} = $2; $idx++;
    }
  }
}

#-----------------------------------------------------------------------------#
sub rearrangeTerms {
  my($subTerm, $value) = @_;
  my($tmpSubTerm, $retVal);

  for $tmpSubTerm ( keys(%subTerms) ) {
    $subTerms{$tmpSubTerm} =~ s!$subTerm!$value!g;
  }

  $retVal = $subTerms{$subTerm};

  delete($subTerms{$subTerm});

  return($retVal);
}

#-----------------------------------------------------------------------------#
sub resolveTerms {
  my($subTerm, $retVal);
  my($modified) = 0;

  while ( scalar(%subTerms) >= 1 ) {
    for $subTerm ( keys(%subTerms) ) {
      if ( $subTerms{$subTerm} =~ m(^(\d+(?:\.\d*)?)([+\-\*/])(\d+(?:\.\d*)?)$) ) {
        $subTerms{$subTerm} = evalSubTerm($1, $2, $3);
        $retVal = rearrangeTerms($subTerm, $subTerms{$subTerm});
      }
    }
  }

  return($retVal);
}

#-----------------------------------------------------------------------------#
while ( $term =~ s/^(.*?)\(([^\(\)]+)\)(.*?)$/$1T$idx$3/ ) {
  $subTerms{"T$idx"} = $2; $idx++;
}

$subTerms{"T0"} = $term;

for $op ( ('\*', '/', '\+', '-') ) { resolveOps($op) };

printf("RESULT: %s\n", resolveTerms());