Lingua::EN::Numbers - turn "407" into "four hundred and seven", etc.

  use Lingua::EN::Numbers qw(num2en num2en_ordinal);

  my $x = 234;
  my $y = 54;
  print "You have ", num2en($x), " things to do today!\n";
  print "You will stop caring after the ", num2en_ordinal($y), ".\n";

  You have two hundred and thirty-four things to do today!
  You will stop caring after the fifty-fourth.

require 5.004;  # Time-stamp: "2005-01-05 17:12:51 AST"
package Lingua::EN::Numbers;

require Exporter;
@ISA = qw(Exporter);

use strict;
BEGIN { *DEBUG = sub () {0} unless defined &DEBUG } # setup a DEBUG constant
use vars qw(
 @EXPORT @EXPORT_OK $VERSION
 $MODE $TRUE $FALSE
 %D %Card2ord %Mult
);
$VERSION = '1.01';
@EXPORT    = ();
@EXPORT_OK = qw( num2en num2en_ordinal );

#--------------------------------------------------------------------------
# Here begins the old junk, including mock-object stuff:

$TRUE = 1; $FALSE = 0; $MODE = "American";
sub import { 
  @_ = grep { $_ ne 'American' and $_ ne 'British' } @_;
  goto &Exporter::import;
}

sub new {
  my $class = shift;
  my $obj = bless [undef],  ref($class) || $class;
  $obj->parse($_[0]);
  return $obj;
}

sub parse { $_[0][0] = $_[1]; return 1; }
sub get_string { num2en( $_[0][0] ); }

# End of legacy stuff.
#--------------------------------------------------------------------------

@D{0 .. 20, 30,40,50,60,70,80,90} = qw|
 zero
 one two three four five six seven eight nine ten
 eleven twelve thirteen fourteen fifteen
 sixteen seventeen eighteen nineteen
 twenty thirty forty fifty sixty seventy eighty ninety
|;


@Card2ord{  qw| one   two    three five  eight  nine  twelve  |}
 =          qw| first second third fifth eighth ninth twelfth |;


{
  my $c = 0;
  for ( '', qw<
    thousand million billion trillion quadrillion quintillion sextillion
    septillion octillion nonillion
  > ) {
    $Mult{$c} = $_;
    $c++;
  }
}

#==========================================================================

sub num2en_ordinal {
   #  Cardinals are [one two three...]
   #  Ordinals  are [first second third...]
  
  return undef unless defined $_[0] and length $_[0];
  my($x) = $_[0];
  
  $x = num2en($x);
  return $x unless $x;
  $x =~ s/(\w+)$//s   or return $x . "th";
  my $last = $1;

  $last =
   $Card2ord{$last} || ( $last =~ s/y$/ieth/ && $last ) || ( $last . "th" );

  return "$x$last";
}

#==========================================================================

sub num2en {
  my $x = $_[0];
  return undef unless defined $x and length $x;

  return 'not-a-number'      if $x eq 'NaN';
  return 'positive infinity' if $x =~ m/^\+inf(?:inity)?$/si;
  return 'negative infinity' if $x =~ m/^\-inf(?:inity)?$/si;
  return          'infinity' if $x =~  m/^inf(?:inity)?$/si;

  return $D{$x} if exists $D{$x};  # the most common cases

  # Make sure it's not in scientific notation:
  {  my $e = _e2en($x);  return $e if defined $e; }
  
  my $orig = $x;

  $x =~ s/,//g; # nix any commas

  my $sign;
  $sign = $1 if $x =~ s/^([-+])//s;
  
  my($int, $fract);
  if(    $x =~ m<^\d+$>          ) { $int = $x }
  elsif( $x =~ m<^(\d+)\.(\d+)$> ) { $int = $1; $fract = $2 }
  elsif( $x =~ m<^\.(\d+)$>      ) { $fract = $1 }
  else {
    DEBUG and print "Not a number: \"orig\"\n";
    return undef;
  }
  
  DEBUG and printf " Working on Sign[%s]  Int2en[%s]  Fract[%s]  < \"%s\"\n",
   map defined($_) ? $_ : "nil", $sign, $int, $fract, $orig;
  
  return join ' ', grep defined($_) && length($_),
    _sign2en($sign),
    _int2en($int),
    _fract2en($fract),
  ;
}

# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

sub _sign2en {
  return undef unless defined $_[0] and length $_[0];  
  return 'negative' if $_[0] eq '-';
  return 'positive' if $_[0] eq '+';
  return "WHAT_IS_$_[0]";
}

sub _fract2en {    # "1234" => "point one two three four"
  return undef unless defined $_[0] and length $_[0];  
  my $x = $_[0];
  return join ' ', 'point', map $D{$_}, split '', $x;
}

# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
# The real work:

sub _int2en {
  return undef unless defined $_[0] and length $_[0]
   and $_[0] =~ m/^\d+$/s;

  my($x) = $_[0];

  return $D{$x} if defined $D{$x};  # most common/irreg cases
  
  if( $x =~ m/^(.)(.)$/ ) {
    return  $D{$1 . '0'} . '-' . $D{$2};
     # like    forty        -     two
      # note that neither bit can be zero at this point
     
  } elsif( $x =~ m/^(.)(..)$/ ) {
    my($h, $rest) = ("$D{$1} hundred", $2);
    return $h if $rest eq '00';
    return "$h and " . _int2en(0 + $rest);
  } else {
    return _bigint2en($x);
  }
}

# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

sub _bigint2en {
  return undef unless defined $_[0] and length $_[0]
   and $_[0] =~ m/^\d+$/s;

  my($x) = $_[0];

  my @chunks;  # each:  [ string, exponent ]
  
  {
    my $groupnum = 0;
    my $num;
    while( $x =~ s<(\d{1,3})$><>s ) { # pull at most three digits from the end
      $num = $1 + 0;
      unshift @chunks, [ $num, $groupnum ] if $num;
      ++$groupnum;
    }
    return $D{'0'} unless @chunks;  # rare but possible
  }
  
  my $and;
  
  $and = 'and' if  $chunks[-1][1] == 0  and  $chunks[-1][0] < 100;
   # The special 'and' that shows up in like "one thousand and eight"
   # and "two billion and fifteen", but not "one thousand [*and] five hundred"
   # or "one million, [*and] nine"

  _chunks2en( \@chunks );

  $chunks[-2] .= " and" if $and and @chunks > 1;
  return "$chunks[0] $chunks[1]" if @chunks == 2;
   # Avoid having a comma if just two units
  return join ", ", @chunks;
}


sub _chunks2en {
  my $chunks = $_[0];
  return unless @$chunks;
  my @out;
  foreach my $c (@$chunks) {
    push @out,   $c = _groupify( _int2en( $c->[0] ),  $c->[1] )  if $c->[0];
  }
  @$chunks = @out;
  return;
}

sub _groupify {
  # turn ("seventeen", 3) => "seventeen billion"
  my($basic, $multnum) = @_;
  return  $basic unless $multnum;  # the first group is unitless
  DEBUG > 2 and print "  Groupifying $basic x $multnum mults\n";
  return "$basic $Mult{$multnum}"  if  $Mult{$multnum};
   # Otherwise it must be huuuuuge, so fake it with scientific notation
  return "$basic " . "times ten to the " . num2en_ordinal($basic * 3);
}

# - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
#
# Because I can never remember this:
#
#  3.1E8
#  ^^^   is called the "mantissa"
#      ^ is called the "exponent"
#         (the implicit "10" is the "base" a/k/a "radix")

sub _e2en {
  my $x = $_[0];

  my($m, $e);
  if( $x =~
    m<
            ^(
                [-+]?  # leading sign
                (?:
                    [\d,]+  |  [\d,]*\.\d+  # number
                )
              )
            [eE]
            (-?\d+)   # mantissa, has to be an integer
            $
        >x
  ) {
    ($m, $e) = ($1, $2);
    DEBUG and print "  Scientific notation: [$x] => $m E $e\n";
    $e += 0;
    return num2en($m) . ' times ten to the ' . num2en_ordinal($e);
  } else {
    DEBUG and print "  Okay, $x isn't in exponential notation\n";
    return undef;
  }
}

#==========================================================================
1;

__END__