allow to call transform's method from the given block

Author: taichi-ishitani

lib/parslet/context.rb

@@ -1,21 +1,46 @@
 # Provides a context for tree transformations to run in. The context allows
 # accessing each of the bindings in the bindings hash as local method.
 #
-# Example: 
+# Example:
 #
 #   ctx = Context.new(:a => :b)
-#   ctx.instance_eval do 
+#   ctx.instance_eval do
 #     a # => :b
 #   end
 #
 # @api private
 class Parslet::Context
   include Parslet
 
-  def initialize(bindings)
+  def initialize(bindings, transform = nil)
+    @__transform = transform if transform
     bindings.each do |key, value|
       singleton_class.send(:define_method, key) { value }
       instance_variable_set("@#{key}", value)
     end
   end
-end
+
+  def respond_to_missing?(method, include_private)
+    @__transform&.respond_to?(method, include_private) || super
+  end
+
+  if RUBY_VERSION >= '3'
+    def method_missing(method, *args, **kwargs, &block)
+      if @__transform&.respond_to?(method)
+        @__transform.__send__(method, *args, **kwargs, &block)
+      else
+        super
+      end
+    end
+  else
+    def method_missing(method, *args, &block)
+      if @__transform&.respond_to?(method)
+        @__transform.__send__(method, *args, &block)
+      else
+        super
+      end
+    end
+
+    ruby2_keywords :method_missing
+  end
+end

lib/parslet/transform.rb

@@ -8,17 +8,17 @@
 # as is into the result tree.
 #
 # This is almost what you would generally do with a tree visitor, except that
-# you can match several levels of the tree at once. 
+# you can match several levels of the tree at once.
 #
 # As a consequence of this, the resulting tree will contain pieces of the
 # original tree and new pieces. Most likely, you will want to transform the
 # original tree wholly, so this isn't a problem.
 #
 # You will not be able to create a loop, given that each node will be replaced
 # only once and then left alone. This means that the results of a replacement
-# will not be acted upon. 
+# will not be acted upon.
 #
-# Example: 
+# Example:
 #
 #   class Example < Parslet::Transform
 #     rule(:string => simple(:x)) {  # (1)
@@ -30,35 +30,35 @@
 # rule can be defined by calling #rule with the pattern as argument. The block
 # given will be called every time the rule matches somewhere in the tree given
 # to #apply. It is passed a Hash containing all the variable bindings of this
-# pattern match. 
-#   
-# In the above example, (1) illustrates a simple matching rule. 
+# pattern match.
+#
+# In the above example, (1) illustrates a simple matching rule.
 #
 # Let's say you want to parse matching parentheses and distill a maximum nest
 # depth. You would probably write a parser like the one in example/parens.rb;
-# here's the relevant part: 
+# here's the relevant part:
 #
 #   rule(:balanced) {
 #     str('(').as(:l) >> balanced.maybe.as(:m) >> str(')').as(:r)
 #   }
 #
 # If you now apply this to a string like '(())', you get a intermediate parse
-# tree that looks like this: 
+# tree that looks like this:
 #
 #   {
-#     l: '(', 
+#     l: '(',
 #     m: {
-#       l: '(', 
-#       m: nil, 
-#       r: ')' 
-#     }, 
-#     r: ')' 
+#       l: '(',
+#       m: nil,
+#       r: ')'
+#     },
+#     r: ')'
 #   }
 #
 # This parse tree is good for debugging, but what we would really like to have
-# is just the nesting depth. This transformation rule will produce that: 
+# is just the nesting depth. This transformation rule will produce that:
 #
-#   rule(:l => '(', :m => simple(:x), :r => ')') { 
+#   rule(:l => '(', :m => simple(:x), :r => ')') {
 #     # innermost :m will contain nil
 #     x.nil? ? 1 : x+1
 #   }
@@ -67,9 +67,9 @@
 #
 # There are four ways of using this class. The first one is very much
 # recommended, followed by the second one for generality. The other ones are
-# omitted here. 
+# omitted here.
 #
-# Recommended usage is as follows: 
+# Recommended usage is as follows:
 #
 #   class MyTransformator < Parslet::Transform
 #     rule(...) { ... }
@@ -78,7 +78,7 @@
 #   end
 #   MyTransformator.new.apply(tree)
 #
-# Alternatively, you can use the Transform class as follows: 
+# Alternatively, you can use the Transform class as follows:
 #
 #   transform = Parslet::Transform.new do
 #     rule(...) { ... }
@@ -87,12 +87,12 @@
 #
 # = Execution context
 #
-# The execution context of action blocks differs depending on the arity of 
-# said blocks. This can be confusing. It is however somewhat intentional. You 
-# should not create fat Transform descendants containing a lot of helper methods, 
+# The execution context of action blocks differs depending on the arity of
+# said blocks. This can be confusing. It is however somewhat intentional. You
+# should not create fat Transform descendants containing a lot of helper methods,
 # instead keep your AST class construction in global scope or make it available
 # through a factory. The following piece of code illustrates usage of global
-# scope: 
+# scope:
 #
 #   transform = Parslet::Transform.new do
 #     rule(...) { AstNode.new(a_variable) }
@@ -109,28 +109,28 @@
 #   transform.apply(tree, :builder => Builder.new)
 #
 # As you can see, Transform allows you to inject local context for your rule
-# action blocks to use. 
+# action blocks to use.
 #
 class Parslet::Transform
   # FIXME: Maybe only part of it? Or maybe only include into constructor
   # context?
-  include Parslet   
-  
+  include Parslet
+
   class << self
     # FIXME: Only do this for subclasses?
     include Parslet
-    
-    # Define a rule for the transform subclass. 
+
+    # Define a rule for the transform subclass.
     #
     def rule(expression, &block)
       @__transform_rules ||= []
       # Prepend new rules so they have higher precedence than older rules
       @__transform_rules.unshift([Parslet::Pattern.new(expression), block])
     end
-    
+
     # Allows accessing the class' rules
     #
-    def rules 
+    def rules
       @__transform_rules ||= []
     end
 
@@ -139,47 +139,47 @@ def inherited(subclass)
       subclass.instance_variable_set(:@__transform_rules, rules.dup)
     end
   end
-  
-  def initialize(raise_on_unmatch=false, &block) 
+
+  def initialize(raise_on_unmatch=false, &block)
     @raise_on_unmatch = raise_on_unmatch
     @rules = []
-    
+
     if block
       instance_eval(&block)
     end
   end
-  
+
   # Defines a rule to be applied whenever apply is called on a tree. A rule
-  # is composed of two parts: 
-  # 
+  # is composed of two parts:
+  #
   # * an *expression pattern*
   # * a *transformation block*
   #
   def rule(expression, &block)
     # Prepend new rules so they have higher precedence than older rules
     @rules.unshift([Parslet::Pattern.new(expression), block])
   end
-  
+
   # Applies the transformation to a tree that is generated by Parslet::Parser
   # or a simple parslet. Transformation will proceed down the tree, replacing
-  # parts/all of it with new objects. The resulting object will be returned. 
+  # parts/all of it with new objects. The resulting object will be returned.
   #
   # Using the context parameter, you can inject bindings for the transformation.
   # This can be used to allow access to the outside world from transform blocks,
   # like so:
-  # 
+  #
   #   document = # some class that you act on
   #   transform.apply(tree, document: document)
-  #   
-  # The above will make document available to all your action blocks: 
+  #
+  # The above will make document available to all your action blocks:
   #
   #   # Variant A
   #   rule(...) { document.foo(bar) }
   #   # Variant B
   #   rule(...) { |d| d[:document].foo(d[:bar]) }
   #
   # @param obj PORO ast to transform
-  # @param context start context to inject into the bindings. 
+  # @param context start context to inject into the bindings.
   #
   def apply(obj, context=nil)
     transform_elt(
@@ -190,52 +190,52 @@ def apply(obj, context=nil)
           recurse_array(obj, context)
       else
         obj
-      end, 
+      end,
       context
     )
   end
-  
+
   # Executes the block on the bindings obtained by Pattern#match, if such a match
-  # can be made. Depending on the arity of the given block, it is called in 
+  # can be made. Depending on the arity of the given block, it is called in
   # one of two environments: the current one or a clean toplevel environment.
   #
-  # If you would like the current environment preserved, please use the 
+  # If you would like the current environment preserved, please use the
   # arity 1 variant of the block. Alternatively, you can inject a context object
   # and call methods on it (think :ctx => self).
   #
   #   # the local variable a is simulated
-  #   t.call_on_match(:a => :b) { a } 
+  #   t.call_on_match(:a => :b) { a }
   #   # no change of environment here
   #   t.call_on_match(:a => :b) { |d| d[:a] }
   #
   def call_on_match(bindings, block)
     if block
       if block.arity == 1
-        return block.call(bindings)
+        return instance_exec(bindings, &block)
       else
-        context = Context.new(bindings)
+        context = Context.new(bindings, self)
         return context.instance_eval(&block)
       end
     end
   end
-  
-  # Allow easy access to all rules, the ones defined in the instance and the 
-  # ones predefined in a subclass definition. 
+
+  # Allow easy access to all rules, the ones defined in the instance and the
+  # ones predefined in a subclass definition.
   #
-  def rules 
+  def rules
     self.class.rules + @rules
   end
-  
-  # @api private 
+
+  # @api private
   #
-  def transform_elt(elt, context) 
+  def transform_elt(elt, context)
     rules.each do |pattern, block|
       if bindings=pattern.match(elt, context)
         # Produces transformed value
         return call_on_match(bindings, block)
       end
     end
-    
+
     # No rule matched - element is not transformed
     if @raise_on_unmatch && elt.is_a?(Hash)
       elt_types = elt.map do |key, value|
@@ -247,19 +247,19 @@ def transform_elt(elt, context)
     end
   end
 
-  # @api private 
+  # @api private
   #
-  def recurse_hash(hsh, ctx) 
+  def recurse_hash(hsh, ctx)
     hsh.inject({}) do |new_hsh, (k,v)|
       new_hsh[k] = apply(v, ctx)
       new_hsh
     end
   end
-  # @api private 
+  # @api private
   #
-  def recurse_array(ary, ctx) 
+  def recurse_array(ary, ctx)
     ary.map { |elt| apply(elt, ctx) }
   end
 end
 
-require 'parslet/context'
+require 'parslet/context'

spec/parslet/transform/context_spec.rb

@@ -1,14 +1,28 @@
 require 'spec_helper'
 
 describe Parslet::Context do
-  def context(*args)
-    described_class.new(*args)
+  let(:transform) do
+    flexmock('transform')
   end
-  
+
+  def context(bindings)
+    described_class.new(bindings, transform)
+  end
+
   it "binds hash keys as variable like things" do
     context(:a => 'value').instance_eval { a }.
       should == 'value'
   end
+  it "responds transform's methods" do
+    transform.should_receive(:foo).and_return { :foo }
+    transform.should_receive(:bar).and_return { :bar }
+
+    c = context(:a => 'value')
+    assert c.respond_to?(:foo)
+    c.foo.should == :foo
+    assert c.respond_to?(:bar)
+    c.bar.should == :bar
+  end
   it "one contexts variables aren't the next ones" do
     ca = context(:a => 'b')
     cb = context(:b => 'c')
@@ -53,4 +67,4 @@ def foo
       end
     end
   end
-end
+end