Beefy Boxes and Bandwidth Generously Provided by pair Networks
Clear questions and runnable code
get the best and fastest answer
 
PerlMonks  

Comment on

by gods
on Feb 11, 2000 at 00:06 UTC ( #3333=superdoc: print w/replies, xml ) Need Help??
To expand (and generalize) on this a bit, let each type of operation have a precedence. Then as you walk the expression tree, you need to parenthesize operations that have a lower precedence than the expression they appear within.

A good way to do this is via OO, representing your operation types as subclasses:

package Op; sub new { my $pkg = shift; bless [@_], $pkg; } sub children { @{ $_[0] } } sub display { my ($self, $precedence) = @_; $precedence = 0 if not defined $precedence; my $s = join $self->op, map { $_->display($self->precedence) } $self->children; $s = "($s)" if $precedence > $self->precedence; return $s; } package Op::Addition; @ISA = qw[Op]; sub precedence { 10 } sub op { " + " } package Op::Multiplication; @ISA = qw[Op]; sub precedence { 20 } sub op { " * " } # ... package Op::Term; @ISA = qw[Op]; sub precedence { 100 } sub display { $_[0][0] }
Then you just call the display method on an Op tree. For example,
Op::Multiplication->new( Op::Term->new(5), Op::Addition->new( Op::Term->new(6), Op::Term->new(7) ) )->display; # 5 * (6 + 7) Op::Addition->new( Op::Term->new(5), Op::Multiplication->new( Op::Term->new(6), Op::Term->new(7) ) )->display; # 5 + 6 * 7
And you can see how easy it would be to add new types of operations, due to the beauty of subclassing.

blokhead


In reply to Re^2: Using overload to parse arithmetic terms by blokhead
in thread Using overload to parse arithmetic terms by esskar

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post; it's "PerlMonks-approved HTML":



  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.
  • Log In?
    Username:
    Password:

    What's my password?
    Create A New User
    Chatterbox?
    and the web crawler heard nothing...

    How do I use this? | Other CB clients
    Other Users?
    Others romping around the Monastery: (4)
    As of 2016-09-25 08:13 GMT
    Sections?
    Information?
    Find Nodes?
    Leftovers?
      Voting Booth?
      Extraterrestrials haven't visited the Earth yet because:







      Results (467 votes). Check out past polls.