feat(combinators): add the ability to ignore a combinator's output in…

… a group

Gemfile.lock

@@ -17,12 +17,12 @@ GEM
       rspec-core (~> 3.12.0)
       rspec-expectations (~> 3.12.0)
       rspec-mocks (~> 3.12.0)
-    rspec-core (3.12.1)
+    rspec-core (3.12.2)
       rspec-support (~> 3.12.0)
-    rspec-expectations (3.12.2)
+    rspec-expectations (3.12.3)
       diff-lcs (>= 1.2.0, < 2.0)
       rspec-support (~> 3.12.0)
-    rspec-mocks (3.12.3)
+    rspec-mocks (3.12.5)
       diff-lcs (>= 1.2.0, < 2.0)
       rspec-support (~> 3.12.0)
     rspec-support (3.12.0)

lib/parsby.rb

@@ -105,7 +105,7 @@ def start(p)
     end
 
     def end(p)
-      Parsby.new("splicer.end(#{p.label})") { |c|
+      Parsby.new("splicer.end(#{p.label})", p.ignore) { |c|
         begin
           p.parse c
         ensure
@@ -600,12 +600,14 @@ def label
   end
 
   attr_writer :label
+  attr_accessor :ignore
 
   # Initialize parser with optional label argument, and parsing block. The
   # parsing block is given an IO as argument, and its result is the result
   # when parsing.
-  def initialize(label = nil, &b)
+  def initialize(label = nil, ignore = false, &b)
     self.label = label if label
+    self.ignore = ignore
     @parser = b
   end
 
@@ -706,7 +708,8 @@ def <<(p)
       x = parse c
       y = p.parse c
       # like x << y, but without modifying x.
-      x + [y]
+      # return x if it is ignored
+      p.ignore ? x : x + [y]
     end
   end
 

lib/parsby/combinators.rb

@@ -21,16 +21,17 @@ def define_combinator(name, wrap: true, &b)
         # Lambda used to access private module method from instance method.
         inspectable_labels_lambda = lambda {|x| inspectable_labels(x) }
 
-        define_method name do |*args, &b2|
+        define_method name do |*args, ignore: false, &b2|
           inspected_args = inspectable_labels_lambda.call(args).map(&:inspect)
           label = name.to_s
           label += "(#{inspected_args.join(", ")})" unless inspected_args.empty?
           # Wrap in new parser so we don't overwrite another automatic
           # label.
           p = m.bind(self).call(*args, &b2)
           if wrap
-            Parsby.new(label) {|c| p.parse c }
+            Parsby.new(label, ignore) {|c| p.parse c }
           else
+            p.ignore = ignore
             p % label
           end
         end