my @table = (
    #### temperature
    [ c => f =>
        sub { ($_[0] * 9/5) + 32 },
        sub { ($_[0] - 32) * 5/9 },
    ],
    [ c => k =>
        sub { $_[0] + 273.16 },
        sub { $_[0] - 273.16 },
    ],

    #### mass/weight
    [ kg   =>  g =>   1000 ],
    [ floz =>  g =>     30 ],
    [ lbs  => kg => 0.4536 ],

    #### distance
    [ ft   => m  =>   0.3048 ],
    [ ft   => in =>       12 ],
    [ in   => cm =>     2.54 ],
    [ m    => cm =>      100 ],
    [ yd   => m  =>   0.9144 ],
    [ km   => m  =>     1000 ],
    [ mile => km => 1.609347 ],
);

my %table;
for my $conv (  @table  ) {
    my( $from, $to, $conv, $rev )= @$conv;
    if(  exists $table{$from}{$to}  ) {
        warn "Duplicate conversions to $to from $from.\n";
    }
    $table{$from}{$to}= $conv;
    if(  $rev  ) {
        if(  exists $table{$from}{$to}  ) {
            warn "Duplicate conversions to $from from $to.\n";
        }
        $table{$to}{$from}= $rev;
    }
}
# Handle reverse conversions when a better one isn't provided:
for my $conv (  @table  ) {
    my( $from, $to, $conv )= @$conv;
    if(  ! ref($conv)  &&  ! exists $table{$to}{$from}  ) {
        $table{$to}{$from}=
            sub { $_[0] / $conv };
    }
}

sub FindConversionPathTo {
    my( $dest, $source )= @_;
    my( @sol );
    $source= { $source => "$source " };
    while(  ! @sol  ) {
        for my $src (  keys %sources  ) {
            if(  exists $table{$src}{$dest}  ) {
                $source{$src} .= "$dest ";
                push @sol, $src;
            } else {
                for my $dest (  keys %{$table{$src}  ) {
                    if(  ! exists $source{$dest}  ) {
                        $source{$dest}=
                            $source{$src} . "$dest ";
                    }
                }
            }
        }
    }
    # Pick one of the solutions at random: (:
    return split ' ', (@source{@sol})[rand @sol];
}