############################################################################
# License
# -------
# The user is free to produce commercial applications with the
# software, to distribute these applications in source or binary form,
# and to charge monies for them as he sees fit and in concordance with
# the laws of the land subject to the following license.
#
# 1. The license applies to all the software and all derived software
# and must appear on such.
#
# 2. It is illegal to distribute the software without this license
# attached to it and use of the software implies agreement with the
# license as such. It is illegal for anyone who is not the copyright
# holder to tamper with or change the license.
#
# 3. Neither the names of Lambda Associates or the copyright holder
# may be used to endorse or promote products built using the software
# without specific prior written permission from the copyright holder.
#
# 4. That possession of this license does not confer on the copyright
# holder any special contractual obligation towards the user. That in
# no event shall the copyright holder be liable for any direct,
# indirect, incidental, special, exemplary or consequential damages
# (including but not limited to procurement of substitute goods or
# services, loss of use, data, or profits; or business interruption),
# however caused and on any theory of liability, whether in contract,
# strict liability or tort (including negligence) arising in any way
# out of the use of the software, even if advised of the possibility
# of such damage.
#
# 5. It is permitted for the user to change the software, for the
# purpose of improving performance, correcting an error, or porting to
# a new platform, and distribute the modified version of Shen
# (hereafter the modified version) provided the resulting program
# conforms in all respects to the Shen standard and is issued under
# that title. The user must make it clear with his distribution that
# he/she is the author of the changes and what these changes are and
# why.
#
# 6. Derived versions of this software in whatever form are subject to
# the same restrictions. In particular it is not permitted to make
# derived copies of this software which do not conform to the Shen
# standard or appear under a different title.
#
# 7. It is permitted to distribute versions of Shen which incorporate
# libraries, graphics or other facilities which are not part of the
# Shen standard.
#
# For an explication of this license see
# http://www.lambdassociates.org/News/june11/license.htm which
# explains this license in full.
#
############################################################################
#
# This file was written by Greg Spurrier as part of the ShenRuby
# project. It is essentially a shell into which the K Lambda sources
# of Shen are loaded at runtime as part of object initialization to
# produce a working Shen environment. It is thefore a derivative work
# of the Shen sources and is subject to the Shen License.
#
############################################################################

module ShenRuby
  # Instances of the ShenRuby::Shen class provide a Shen environment
  # running within a Klam environment
  class Shen < Klam::Environment
    def initialize
      super

      # Set the global variables
      set("*language*".to_sym, "Ruby")
      set("*implementation*".to_sym, "#{::RUBY_ENGINE} #{::RUBY_VERSION}")
      set("*release*".to_sym, ::RUBY_VERSION)
      set("*port*".to_sym, ::ShenRuby::VERSION)
      set("*porters*".to_sym, "Greg Spurrier")
      set("*home-directory*".to_sym, ::Dir.pwd)
      set("*stinput*".to_sym, ::STDIN)
      set("*stoutput*".to_sym, ::STDOUT)

      # Load the K Lambda files
      kl_root = ::File.expand_path('../../../release/k_lambda', __FILE__)
      %w(toplevel core sys).each do |kl_filename|
        ::ShenRuby::Shen.load_file(self, ::File.join(kl_root, kl_filename + ".kl"))
      end

      # Overrides
      class << self
        # Give a way to bail out
        def quit
          ::Kernel.exit(0)
        end

        # Add a way to evaluate strings, intended for use with Ruby interop.
        # Returns the result of the last expression evaluated.
        def eval_string(s)
          forms = __send__(:"read-from-string", s)
          result = nil
          while forms
            result = eval(head(forms))
            forms = tail(forms)
          end
          result
        end
        alias_method :"eval-string", :eval_string

        # The performance of `element?` is critical
        def element?(x, l)
          while l
            return true if l.hd == x
            l = l.tl
          end
          return false
        rescue => e
          __send(:"shen.sys-error", :element?)
        end

        def vector(n)
          v = ::Klam::Absvector.new(n + 1, :"shen.fail!")
          v[0] = n
          v
        end
      end

      # Load the rest of the K Lambda files
      %w(sequent yacc
         reader prolog track load writer
         macros declarations t-star types
        ).each do |kl_filename|
        ::ShenRuby::Shen.load_file(self, ::File.join(kl_root, kl_filename + ".kl"))
      end

      # Give type signatures to the new functions added above
      declare :quit, cons(:"-->", cons(:unit, nil))
      declare :eval_string, cons(:string, cons(:"-->", cons(:unit, nil)))
      declare :"eval-string", cons(:string, cons(:"-->", cons(:unit, nil)))
    end

    class << self
      def load_file(env, path)
        ::File.open(path, 'r') do |file|
          reader = ::Klam::Reader.new(file)
          while form = reader.next
            env.__send__(:"eval-kl", form)
          end
        end
      end
    end
  end
end