use Math::Symbolic qw/parse_from_string/;

my $ms;
eval { $ms = parse_from_string($expression) };
if ($@) {...} # catch parse errors

my $value;
eval { $value = $ms->value() };
if ($@) {...} # catch execution errors

##</code><code>##

# parse...

unless ( $ms->is_constant() ) {
  # complain about variables in the tree
}

my $value;
eval { $value = $ms->value() };
if ($@) {...} # catch execution errors

##</code><code>##

# parse...

# note the parens for list context
my ($coderef) = $ms->to_sub();
my $value = $coderef->();