Question

I am working on a building a compiler and within that I generate a tree that represents the source program that is passed in. I want to display this is a tree like fashion so I can display the structure of the program to anyone interested.

Right now I just have the tree printing on a single line like this:

ProgramNode -> 'Math' BlockNode -> DeclarationNode -> ConstantDeclarationNode -> const ConstantListNode -> [m := 7, ConstantANode -> [n := StringLiteralNode -> ""TEST"" ]] ; 

What I would like is something like this:

   ProgramNode 
    /     \
'Math' BlockNode
           |
    DeclarationNode
           |
    ConstantDeclarationNode ------------------------------
        /      \                                         |
     const ConstantListNode                              |
             /  |  \      \                              |
             m  :=  7    ConstantANode                   |
                            /  |    \                    |
                           n   :=  StringLiteralNode     |
                                      /    |   \         |
                                      "   TEST  "        ;

I haven’t really worked with trees in Ruby, how are they usually represented?

Any help would be appreciated.

Answer 1

This kind of pretty printing requires quite a bit of math. Besides, it’s unclear what should happen if the tree grows too wide for the console window. I don’t know of any existing libraries that’ll do this. I personally use awesome_print.

tree = {'ConstantDeclarationNode' => ['const',
                                      'ConstantListNode' => ['m', ':=', '7']]}

require 'awesome_print'

ap tree
# >> {
# >>     "ConstantDeclarationNode" => [
# >>         [0] "const",
# >>         [1] {
# >>             "ConstantListNode" => [
# >>                 [0] "m",
# >>                 [1] ":=",
# >>                 [2] "7"
# >>             ]
# >>         }
# >>     ]
# >> }

It has tons of options, check it out!