Class: Dentaku::Parser

Inherits:
Object
  • Object
show all
Defined in:
lib/dentaku/parser.rb

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(tokens, options = {}) ⇒ Parser

Returns a new instance of Parser.



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# File 'lib/dentaku/parser.rb', line 7

def initialize(tokens, options={})
  @input      = tokens.dup
  @output     = []
  @operations = options.fetch(:operations, [])
  @arities    = options.fetch(:arities, [])
end

Instance Attribute Details

#arities ⇒ Object (readonly)

Returns the value of attribute arities.



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# File 'lib/dentaku/parser.rb', line 5

def arities
  @arities
end

#input ⇒ Object (readonly)

Returns the value of attribute input.



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# File 'lib/dentaku/parser.rb', line 5

def input
  @input
end

#operations ⇒ Object (readonly)

Returns the value of attribute operations.



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# File 'lib/dentaku/parser.rb', line 5

def operations
  @operations
end

#output ⇒ Object (readonly)

Returns the value of attribute output.



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# File 'lib/dentaku/parser.rb', line 5

def output
  @output
end

Instance Method Details

#consume(count = 2) ⇒ Object 



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# File 'lib/dentaku/parser.rb', line 18

def consume(count=2)
  operator = operations.pop
  output.push operator.new(*get_args(operator.arity || count))
end

#function(token) ⇒ Object 



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# File 'lib/dentaku/parser.rb', line 227

def function(token)
  Dentaku::AST::Function.get(token.value)
end

#get_args(count) ⇒ Object 



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# File 'lib/dentaku/parser.rb', line 14

def get_args(count)
  Array.new(count) { output.pop }.reverse
end

#operation(token) ⇒ Object 



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# File 'lib/dentaku/parser.rb', line 205

def operation(token)
  {
    add:      AST::Addition,
    subtract: AST::Subtraction,
    multiply: AST::Multiplication,
    divide:   AST::Division,
    pow:      AST::Exponentiation,
    negate:   AST::Negation,
    mod:      AST::Modulo,

    lt:       AST::LessThan,
    gt:       AST::GreaterThan,
    le:       AST::LessThanOrEqual,
    ge:       AST::GreaterThanOrEqual,
    ne:       AST::NotEqual,
    eq:       AST::Equal,

    and:      AST::And,
    or:       AST::Or,
  }.fetch(token.value)
end

#parse ⇒ Object 



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# File 'lib/dentaku/parser.rb', line 23

def parse
  return AST::Nil.new if input.empty?

  while token = input.shift
    case token.category
    when :numeric
      output.push AST::Numeric.new(token)

    when :logical
      output.push AST::Logical.new(token)

    when :string
      output.push AST::String.new(token)

    when :identifier
      output.push AST::Identifier.new(token)

    when :operator, :comparator, :combinator
      op_class = operation(token)

      if op_class.right_associative?
        while operations.last && operations.last < AST::Operation && op_class.precedence < operations.last.precedence
          consume
        end

        operations.push op_class
      else
        while operations.last && operations.last < AST::Operation && op_class.precedence <= operations.last.precedence
          consume
        end

        operations.push op_class
      end

    when :null
      output.push AST::Nil.new

    when :function
      arities.push 0
      operations.push function(token)

    when :case
      case token.value
      when :open
        # special handling for case nesting: strip out inner case
        # statements and parse their AST segments recursively
        if operations.include?(AST::Case)
          open_cases = 0
          case_end_index = nil

          input.each_with_index do |token, index|
            if token.category == :case && token.value == :open
              open_cases += 1
            end

            if token.category == :case && token.value == :close
              if open_cases > 0
                open_cases -= 1
              else
                case_end_index = index
                break
              end
            end
          end
          inner_case_inputs = input.slice!(0..case_end_index)
          subparser = Parser.new(
            inner_case_inputs,
            operations: [AST::Case],
            arities: [0]
          )
          subparser.parse
          output.concat(subparser.output)
        else
          operations.push AST::Case
          arities.push(0)
        end
      when :close
        if operations[1] == AST::CaseThen
          while operations.last != AST::Case
            consume
          end

          operations.push(AST::CaseConditional)
          consume(2)
          arities[-1] += 1
        elsif operations[1] == AST::CaseElse
          while operations.last != AST::Case
            consume
          end

          arities[-1] += 1
        end

        unless operations.count == 1 && operations.last == AST::Case
          fail ParseError, "Unprocessed token #{ token.value }"
        end
        consume(arities.pop.succ)
      when :when
        if operations[1] == AST::CaseThen
          while ![AST::CaseWhen, AST::Case].include?(operations.last)
            consume
          end
          operations.push(AST::CaseConditional)
          consume(2)
          arities[-1] += 1
        elsif operations.last == AST::Case
          operations.push(AST::CaseSwitchVariable)
          consume
        end

        operations.push(AST::CaseWhen)
      when :then
        if operations[1] == AST::CaseWhen
          while ![AST::CaseThen, AST::Case].include?(operations.last)
            consume
          end
        end
        operations.push(AST::CaseThen)
      when :else
        if operations[1] == AST::CaseThen
          while operations.last != AST::Case
            consume
          end

          operations.push(AST::CaseConditional)
          consume(2)
          arities[-1] += 1
        end

        operations.push(AST::CaseElse)
      else
        fail ParseError, "Unknown case token #{ token.value }"
      end

    when :grouping
      case token.value
      when :open
        if input.first && input.first.value == :close
          input.shift
          consume(0)
        else
          operations.push AST::Grouping
        end

      when :close
        while operations.any? && operations.last != AST::Grouping
          consume
        end

        lparen = operations.pop
        fail ParseError, "Unbalanced parenthesis" unless lparen == AST::Grouping

        if operations.last && operations.last < AST::Function
          consume(arities.pop.succ)
        end

      when :comma
        arities[-1] += 1
        while operations.any? && operations.last != AST::Grouping
          consume
        end

      else
        fail ParseError, "Unknown grouping token #{ token.value }"
      end

    else
      fail ParseError, "Not implemented for tokens of category #{ token.category }"
    end
  end

  while operations.any?
    consume
  end

  unless output.count == 1
    fail ParseError, "Invalid statement"
  end

  output.first
end