Now ignorable. Needs refactor to extract the logic out to an applicative

TODO: #2

spec/ast_spec.cr

@@ -36,4 +36,21 @@ describe Pegasus::ParseTree do
     res = parser.parse("abcdef")
     res.parse_tree.dump.should eq(expected_parse_tree.dump)
   end
+
+  it "ignores ignored nodes while still matching" do
+    parser = Pegasus::Parser.define do |p|
+      p.rule(:def) { |p| p.str("def") }
+      p.rule(:abcdef) { |p| p.rule(:abc).aka(:a2c) >> p.rule(:def).ignore }
+      p.rule(:abc) { |p| p.str("abc") }
+
+      p.root(:abcdef)
+    end
+
+    expected_parse_tree = Pegasus::Branch(String).new(:seq).tap do |tree|
+      tree << Pegasus::Leaf.new(:a2c, "abc")
+    end
+
+    res = parser.parse("abcdef")
+    res.parse_tree.dump.should eq(expected_parse_tree.dump)
+  end
 end

src/pegasus/ast.cr

@@ -17,6 +17,10 @@ module Pegasus
       to_json
     end
 
+    def prune
+      self
+    end
+
     JSON.mapping(
       label: Symbol,
       item: T
@@ -46,6 +50,14 @@ module Pegasus
       to_json
     end
 
+    def prune
+      Branch(T).new(@label).tap do |branch|
+        @children.each do |child|
+          branch << child if child.label != :ignore
+        end
+      end
+    end
+
     JSON.mapping(
       label: Symbol,
       children: Array(Branch(T) | Leaf(T))

src/pegasus/extensions/ignored.cr

@@ -9,7 +9,11 @@ module Pegasus
         old_context = context.dup
         match, _ = @rule.match?(context)
 
-        {match, old_context}
+        if match.success?
+          {MatchResult.success(Leaf.new(@label, match.parse_tree.value)), old_context}
+        else
+          {MatchResult.failure(Leaf.new(@label, match.parse_tree.value)), old_context}
+        end
       end
 
       def flatten

src/pegasus/match_result.cr

@@ -3,6 +3,7 @@ module Pegasus
     getter :parse_tree
 
     def initialize(@result : Bool, @parse_tree : Pegasus::ParseTree)
+      @parse_tree = parse_tree.prune
     end
 
     def self.success(tree : Pegasus::ParseTree)