Class: SexpProcessor

Inherits:
Object show all
Defined in:
lib/sexp_processor.rb

Overview

SexpProcessor provides a uniform interface to process Sexps.

In order to create your own SexpProcessor subclass you’ll need to call super in the initialize method, then set any of the Sexp flags you want to be different from the defaults.

SexpProcessor uses a Sexp’s type to determine which process method to call in the subclass. For Sexp s(:lit, 1) SexpProcessor will call #process_lit, if it is defined.

You can also specify a default method to call for any Sexp types without a process_<type> method or use the default processor provided to skip over them.

Here is a simple example:

class MyProcessor < SexpProcessor
  def initialize
    super
    self.strict = false
  end

  def process_lit(exp)
    val = exp.shift
    return val
  end
end

Direct Known Subclasses

CompositeSexpProcessor

Defined Under Namespace

Classes: Environment

Constant Summary collapse

VERSION = 
'4.0.1'

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize ⇒ SexpProcessor

Creates a new SexpProcessor. Use super to invoke this initializer from SexpProcessor subclasses, then use the attributes above to customize the functionality of the SexpProcessor



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# File 'lib/sexp_processor.rb', line 102

def initialize
  @default_method      = nil
  @warn_on_default     = true
  @auto_shift_type     = false
  @strict              = false
  @unsupported         = [:alloca, :cfunc, :cref, :ifunc, :last, :memo,
                          :newline, :opt_n, :method]
  @unsupported_checked = false
  @debug               = {}
  @expected            = Sexp
  @require_empty       = true
  @exceptions          = {}

  # we do this on an instance basis so we can subclass it for
  # different processors.
  @processors = {}
  @rewriters  = {}
  @context    = []

  public_methods.each do |name|
    case name
    when /^process_(.*)/ then
      @processors[$1.to_sym] = name.to_sym
    when /^rewrite_(.*)/ then
      @rewriters[$1.to_sym]  = name.to_sym
    end
  end
end

Instance Attribute Details

#auto_shift_type ⇒ Object

Automatically shifts off the Sexp type before handing the Sexp to process_<type>



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# File 'lib/sexp_processor.rb', line 43

def auto_shift_type
  @auto_shift_type
end

#context ⇒ Object (readonly)

Return a stack of contexts. Most recent node is first.



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# File 'lib/sexp_processor.rb', line 48

def context
  @context
end

#debug ⇒ Object

A Hash of Sexp types and Regexp.

Print a debug message if the Sexp type matches the Hash key and the Sexp’s #inspect output matches the Regexp.



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# File 'lib/sexp_processor.rb', line 56

def debug
  @debug
end

#default_method ⇒ Object

A default method to call if a process_<type> method is not found for the Sexp type.



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# File 'lib/sexp_processor.rb', line 62

def default_method
  @default_method
end

#env ⇒ Object (readonly)

A scoped environment to make you happy.



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# File 'lib/sexp_processor.rb', line 94

def env
  @env
end

#expected ⇒ Object

Expected result class



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# File 'lib/sexp_processor.rb', line 67

def expected
  @expected
end

#require_empty ⇒ Object

Raise an exception if the Sexp is not empty after processing



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# File 'lib/sexp_processor.rb', line 72

def require_empty
  @require_empty
end

#strict ⇒ Object

Raise an exception if no process_<type> method is found for a Sexp.



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# File 'lib/sexp_processor.rb', line 77

def strict
  @strict
end

#unsupported ⇒ Object

An array that specifies node types that are unsupported by this processor. SexpProcessor will raise UnsupportedNodeError if you try to process one of those node types.



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# File 'lib/sexp_processor.rb', line 84

def unsupported
  @unsupported
end

#warn_on_default ⇒ Object

Emit a warning when the method in #default_method is called.



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# File 'lib/sexp_processor.rb', line 89

def warn_on_default
  @warn_on_default
end

Instance Method Details

#assert_empty(meth, exp, exp_orig) ⇒ Object 



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# File 'lib/sexp_processor.rb', line 131

def assert_empty(meth, exp, exp_orig)
  unless exp.empty? then
    msg = "exp not empty after #{self.class}.#{meth} on #{exp.inspect}"
    msg += " from #{exp_orig.inspect}" if $DEBUG
    raise NotEmptyError, msg
  end
end

#assert_type(list, typ) ⇒ Object

Raises unless the Sexp type for list matches typ

Raises:



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# File 'lib/sexp_processor.rb', line 269

def assert_type(list, typ)
  raise SexpTypeError, "Expected type #{typ.inspect} in #{list.inspect}" if
    not Array === list or list.first != typ
end

#error_handler(type, exp = nil) ⇒ Object

:nodoc:



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# File 'lib/sexp_processor.rb', line 274

def error_handler(type, exp=nil) # :nodoc:
  begin
    return yield
  rescue StandardError => err
    if @exceptions.has_key? type then
      return @exceptions[type].call(self, exp, err)
    else
      warn "#{err.class} Exception thrown while processing #{type} for sexp #{exp.inspect} #{caller.inspect}" if $DEBUG
      raise
    end
  end
end

#in_context(type) ⇒ Object 



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# File 'lib/sexp_processor.rb', line 338

def in_context type
  self.context.unshift type

  yield

  self.context.shift
end

#on_error_in(node_type, &block) ⇒ Object

Registers an error handler for node



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# File 'lib/sexp_processor.rb', line 290

def on_error_in(node_type, &block)
  @exceptions[node_type] = block
end

#process(exp) ⇒ Object

Default Sexp processor. Invokes process_<type> methods matching the Sexp type given. Performs additional checks as specified by the initializer.



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# File 'lib/sexp_processor.rb', line 172

def process(exp)
  return nil if exp.nil?
  if self.context.empty? then
    p :rewriting unless debug.empty?
    exp = self.rewrite(exp)
    p :done_rewriting unless debug.empty?
  end

  unless @unsupported_checked then
    m = public_methods.grep(/^process_/) { |o| o.to_s.sub(/^process_/, '').to_sym }
    supported = m - (m - @unsupported)

    raise UnsupportedNodeError, "#{supported.inspect} shouldn't be in @unsupported" unless supported.empty?

    @unsupported_checked = true
  end

  result = self.expected.new

  type = exp.first
  raise "type should be a Symbol, not: #{exp.first.inspect}" unless
    Symbol === type

  in_context type do
    if @debug.has_key? type then
      str = exp.inspect
      puts "// DEBUG:(original ): #{str}" if str =~ @debug[type]
    end

    exp_orig = nil
    exp_orig = exp.deep_clone if $DEBUG or
      @debug.has_key? type or @exceptions.has_key?(type)

    raise UnsupportedNodeError, "'#{type}' is not a supported node type" if
      @unsupported.include? type

    # now do a pass with the real processor (or generic)
    meth = @processors[type] || @default_method
    if meth then

      if @warn_on_default and meth == @default_method then
        warn "WARNING: Using default method #{meth} for #{type}"
      end

      exp.shift if @auto_shift_type and meth != @default_method

      result = error_handler(type, exp_orig) do
        self.send(meth, exp)
      end

      if @debug.has_key? type then
        str = exp.inspect
        puts "// DEBUG (processed): #{str}" if str =~ @debug[type]
      end

      raise SexpTypeError, "Result must be a #{@expected}, was #{result.class}:#{result.inspect}" unless @expected === result

      self.assert_empty(meth, exp, exp_orig) if @require_empty
    else
      unless @strict then
        until exp.empty? do
          sub_exp = exp.shift
          sub_result = nil
          if Array === sub_exp then
            sub_result = error_handler(type, exp_orig) do
              process(sub_exp)
            end
            raise "Result is a bad type" unless Array === sub_exp
            raise "Result does not have a type in front: #{sub_exp.inspect}" unless Symbol === sub_exp.first unless sub_exp.empty?
          else
            sub_result = sub_exp
          end
          result << sub_result
        end

        # NOTE: this is costly, but we are in the generic processor
        # so we shouldn't hit it too much with RubyToC stuff at least.
        #if Sexp === exp and not exp.sexp_type.nil? then
        begin
          result.sexp_type = exp.sexp_type
        rescue Exception
          # nothing to do, on purpose
        end
      else
        msg = "Bug! Unknown node-type #{type.inspect} to #{self.class}"
        msg += " in #{exp_orig.inspect} from #{caller.inspect}" if $DEBUG
        raise UnknownNodeError, msg
      end
    end
  end

  result
end

#process_dummy(exp) ⇒ Object

A fairly generic processor for a dummy node. Dummy nodes are used when your processor is doing a complicated rewrite that replaces the current sexp with multiple sexps.

Bogus Example:

def process_something(exp)
  return s(:dummy, process(exp), s(:extra, 42))
end



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# File 'lib/sexp_processor.rb', line 305

def process_dummy(exp)
  result = @expected.new(:dummy) rescue @expected.new

  until exp.empty? do
    result << self.process(exp.shift)
  end

  result
end

#rewrite(exp) ⇒ Object 



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# File 'lib/sexp_processor.rb', line 139

def rewrite(exp)
  type = exp.first

  if @debug.has_key? type then
    str = exp.inspect
    puts "// DEBUG (original ): #{str}" if str =~ @debug[type]
  end

  in_context type do
    exp.map! { |sub| Array === sub ? rewrite(sub) : sub }
  end

  begin
    meth = @rewriters[type]
    exp  = self.send(meth, exp) if meth
    break unless Sexp === exp

    if @debug.has_key? type then
      str = exp.inspect
      puts "// DEBUG (rewritten): #{str}" if str =~ @debug[type]
    end

    old_type, type = type, exp.first
  end until old_type == type

  exp
end

#scope(&block) ⇒ Object

Add a scope level to the current env. Eg:

def process_defn exp
  name = exp.shift
  args = process(exp.shift)
  scope do
    body = process(exp.shift)
    # ...
  end
end

env[:x] = 42
scope do
  env[:x]       # => 42
  env[:y] = 24
end
env[:y]         # => nil



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# File 'lib/sexp_processor.rb', line 334

def scope &block
  env.scope(&block)
end