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 Nary
  15 
  16  module Branch
  17 
  18  module Rule
  19 
  20  class Cond < Abstraction::HasHead
  21      alias head_expr head
  22  end
  23 
  24  end # Umu::ConcreteSyntax::Core::Expression::Nary::Branch::Rule
  25 
  26 
  27 
  28  class Cond < Abstract
  29 
  30  private
  31 
  32      def __keyword__
  33          'cond'
  34      end
  35 
  36 
  37      def __desugar__(env, event)
  38          new_env = env.enter event
  39 
  40          opnd_expr = self.expr.desugar(new_env)
  41          ASSERT.kind_of opnd_expr, ASCE::Abstract
  42          if opnd_expr.simple? || self.rules.size <= 1
  43              rules = __desugar_rules__(env) { |_| opnd_expr }
  44 
  45              ASCE.make_if self.loc, rules, self.desugar_else_expr(new_env)
  46          else
  47              ASCE.make_let(
  48                  self.loc,
  49 
  50                  ASCD.make_seq_of_declaration(
  51                      opnd_expr.loc,
  52                      [ASCD.make_value(opnd_expr.loc, :'%x', opnd_expr)]
  53                  ),
  54 
  55                  ASCE.make_if(
  56                      self.loc,
  57                      __desugar_rules__(env) { |loc|
  58                          ASCE.make_identifier loc, :'%x'
  59                      },
  60                      self.desugar_else_expr(new_env)
  61                  )
  62              )
  63          end
  64      end
  65 
  66 
  67      def __desugar_rules__(env, &fn)
  68          self.rules.map { |rule|
  69              ASSERT.kind_of rule, Rule::Cond
  70 
  71              opr_expr    = rule.head_expr.desugar env
  72              head_expr   = ASCE.make_apply(
  73                                  rule.loc, opr_expr, fn.call(rule.loc)
  74                              )
  75              body_expr   = self.desugar_body_expr env, rule
  76 
  77              ASCE.make_rule rule.loc, head_expr, body_expr
  78          }
  79      end
  80  end
  81 
  82  end # Umu::ConcreteSyntax::Core::Expression::Nary::Branch
  83 
  84  end # Umu::ConcreteSyntax::Core::Expression::Nary
  85 
  86 
  87  module_function
  88 
  89      def make_cond_rule(loc, head_expr, body_expr)
  90          ASSERT.kind_of loc,         LOC::Entry
  91          ASSERT.kind_of head_expr,   CSCE::Abstract
  92          ASSERT.kind_of body_expr,   CSCE::Abstract
  93 
  94          Nary::Branch::Rule::Cond.new(loc, head_expr, body_expr).freeze
  95      end
  96 
  97 
  98      def make_cond(loc, expr, fst_rule, snd_rules, opt_else_expr)
  99          ASSERT.kind_of      loc,            LOC::Entry
 100          ASSERT.kind_of      expr,           CSCE::Abstract
 101          ASSERT.kind_of      fst_rule,       CSCEN::Branch::Rule::Cond
 102          ASSERT.kind_of      snd_rules,      ::Array
 103          ASSERT.opt_kind_of  opt_else_expr,  CSCE::Abstract
 104 
 105          Nary::Branch::Cond.new(
 106              loc, expr, fst_rule, snd_rules, opt_else_expr
 107          ).freeze
 108      end
 109 
 110  end # Umu::ConcreteSyntax::Core::Expression
 111 
 112  end # Umu::ConcreteSyntax::Core
 113 
 114  end # Umu::ConcreteSyntax
 115 
 116  end # Umu