1  # coding: utf-8
   2  # frozen_string_literal: true
   3 
   4 
   5 
   6  module Umu
   7 
   8  module ConcreteSyntax
   9 
  10  module Core
  11 
  12  module Expression
  13 
  14  module MemoStream
  15 
  16  class Abstract < Expression::Abstract; end
  17 
  18 
  19 
  20 
  21  class Nil < Abstract
  22      def to_s
  23          '&{}'
  24      end
  25 
  26 
  27      def pretty_print(q)
  28          q.text '&{}'
  29      end
  30 
  31 
  32  private
  33 
  34      def __desugar__(env, event)
  35          ASCE.make_memo_stream_nil self.loc
  36      end
  37  end
  38 
  39 
  40 
  41  class Cons < Abstract
  42      attr_reader :head_expr, :tail_expr
  43 
  44      def initialize(loc, head_expr, tail_expr)
  45          ASSERT.kind_of head_expr,   CSCE::Abstract
  46          ASSERT.kind_of tail_expr,   CSCE::Abstract
  47 
  48          super(loc)
  49 
  50          @head_expr = head_expr
  51          @tail_expr = tail_expr
  52      end
  53 
  54 
  55      def to_s
  56          format("&{%s | %s}",
  57              self.head_expr.to_s,
  58              self.tail_expr.to_s
  59          )
  60      end
  61 
  62 
  63      def pretty_print(q)
  64          PRT.group q, bb:'&{', eb:'}' do
  65              q.pp self.head_expr
  66 
  67              q.breakable
  68 
  69              q.text '|'
  70 
  71              q.breakable
  72 
  73              q.pp self.tail_expr
  74          end
  75      end
  76 
  77 
  78  private
  79 
  80      def __desugar__(env, event)
  81          new_env = env.enter event
  82 
  83          ASCE.make_memo_stream_cons(
  84              self.loc,
  85              self.head_expr.desugar(new_env),
  86              self.tail_expr.desugar(new_env)
  87          )
  88      end
  89  end
  90 
  91  end # Umu::ConcreteSyntax::Core::Expression::MemoStream
  92 
  93 
  94  module_function
  95 
  96      def make_memo_stream_nil(loc)
  97          ASSERT.kind_of loc, LOC::Entry
  98 
  99          MemoStream::Nil.new(loc).freeze
 100      end
 101 
 102 
 103      def make_memo_stream_cons(loc, head_expr, tail_expr)
 104          ASSERT.kind_of loc,         LOC::Entry
 105          ASSERT.kind_of head_expr,   CSCE::Abstract
 106          ASSERT.kind_of tail_expr,   CSCE::Abstract
 107 
 108          MemoStream::Cons.new(loc, head_expr, tail_expr).freeze
 109      end
 110 
 111  end # Umu::ConcreteSyntax::Core::Expression
 112 
 113  end # Umu::ConcreteSyntax::Core
 114 
 115  end # Umu::ConcreteSyntax
 116 
 117  end # Umu