Add a basic tree data structure.

src/chalk/print_visitor.cr

@@ -0,0 +1,68 @@
+require "./tree.cr"
+
+module Chalk
+    class PrintVisitor < Visitor
+        def initialize
+            @indent = 0
+        end
+
+        def print_indent
+            @indent.times do
+                STDOUT << "  "
+            end
+        end
+
+        def visit(id : TreeId)
+            print_indent
+            puts id.id
+        end
+
+        def visit(lit : TreeLit)
+            print_indent
+            puts lit.lit
+        end
+
+        def visit(op : TreeOp)
+            print_indent
+            STDOUT << "[op] "
+            puts op.op
+            @indent += 1
+        end
+
+        def finish(op : TreeOp)
+            @indent -= 1
+        end
+
+        def visit(function : TreeFunction)
+            print_indent
+            STDOUT << "[function] " << function.name << "( "
+            function.params.each do |param|
+                STDOUT << param << " "
+            end
+            puts ")"
+            @indent += 1
+        end
+
+        def finish(function : TreeFunction)
+            @indent -= 1
+        end
+
+        macro forward(text, type)
+            def visit(tree : {{type}})
+                print_indent
+                puts {{text}}
+                @indent += 1
+            end
+
+            def finish(tree : {{type}})
+                @indent -= 1
+            end
+        end
+
+        forward("[block]", TreeBlock)
+        forward("[var]", TreeVar)
+        forward("[if]", TreeIf)
+        forward("[while]", TreeWhile)
+        forward("[return]", TreeReturn)
+    end
+end

src/chalk/tree.cr

@@ -0,0 +1,114 @@
+module Chalk
+    class Visitor
+        def visit(tree : Tree)
+        end
+
+        def finish(tree : Tree)
+        end
+    end
+
+    class Tree
+        def accept(v : Visitor)
+            v.visit(self)
+            v.finish(self)
+        end
+    end
+
+    class TreeId < Tree
+        property id : String
+        def initialize(@id : String) end
+    end
+
+    class TreeLit < Tree
+        property lit : Int64
+        def initialize(@lit : Int64) end
+    end
+
+    class TreeOp < Tree
+        property op : TokenType
+        property left : Tree
+        property right : Tree
+        def initialize(@op : TokenType, @left : Tree, @right : Tree) end
+
+        def accept(v : Visitor)
+            v.visit(self)
+            @left.accept(v)
+            @right.accept(v)
+            v.finish(self)
+        end
+    end
+
+    class TreeBlock < Tree
+        def initialize(@children : Array(Tree)) end
+
+        def accept(v : Visitor)
+            v.visit(self)
+            @children.each &.accept(v)
+            v.finish(self)
+        end
+    end
+
+    class TreeFunction < Tree
+        property name : String
+        property params : Array(String)
+        property block : Tree
+
+        def initialize(@name : String, @params : Array(String), @block : Tree) end
+        def accept(v : Visitor)
+            v.visit(self)
+            @block.accept(v)
+            v.finish(self)
+        end
+    end
+
+    class TreeVar < Tree
+        property name : String
+        property expr : Tree
+
+        def initialize(@name : String, @expr : Tree) end
+        def accept(v : Visitor)
+            v.visit(self)
+            @expr.accept(v)
+            v.finish(self)
+        end
+    end
+
+    class TreeIf < Tree
+        property condition : Tree
+        property block : Tree
+        property otherwise : Tree
+
+        def initialize(@condition : Tree, @block : Tree, @otherwise : Tree) end
+        def accept(v : Visitor)
+            v.visit(self)
+            @condition.accept(v)
+            @block.accept(v)
+            @otherwise.accept(v)
+            v.finish(self)
+        end
+    end
+
+    class TreeWhile < Tree
+        property condition : Tree
+        property block : Tree
+
+        def initialize(@condition : Tree, @block : Tree) end
+        def accept(v : Visitor)
+            v.visit(self)
+            @condition.accept(v)
+            @block.accept(v)
+            v.finish(self)
+        end
+    end
+
+    class TreeReturn < Tree
+        property rvalue : Tree
+        
+        def initialize(@rvalue : Tree) end
+        def accept(v : Visitor)
+            v.visit(self)
+            @rvalue.accept(v)
+            v.finish(self)
+        end
+    end
+end