Class: Baba::Parser

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

Defined Under Namespace

Classes: ParserError

Constant Summary collapse

BREAKING_TOKENS = 
[THING, DOES, VAR, FOR, IF, WHILE, RETURN, BREAK]

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(tokens) ⇒ Parser

Returns a new instance of Parser.



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

def initialize(tokens)
  @tokens = tokens
  @current = 0
end

Instance Attribute Details

#current ⇒ Object (readonly)

Returns the value of attribute current.



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# File 'lib/baba/parser.rb', line 12

def current
  @current
end

#tokens ⇒ Object (readonly)

Returns the value of attribute tokens.



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# File 'lib/baba/parser.rb', line 12

def tokens
  @tokens
end

Instance Method Details

#advance ⇒ Object 



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# File 'lib/baba/parser.rb', line 387

def advance
  @current += 1 if !eof?
  previous()
end

#assignment ⇒ Object 



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# File 'lib/baba/parser.rb', line 201

def assignment
  expr = expr_or()

  if match(EQUAL)
    equals = previous()
    value = assignment()

    if expr.is_a?(Expr::Variable)
      name = expr.name
      return Expr::Assign.new(name, value)
    elsif expr.is_a?(Expr::Get)
      return Expr::Set.new(expr.object, expr.name, value)
    end

    error(equals, "Invalid assignment target.")
  end

  expr
end

#block ⇒ Object 



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# File 'lib/baba/parser.rb', line 189

def block
  statements = []
  until check(KEND) || check(ELSE) || eof?
    statements << declaration()
  end

  unless check(ELSE)
    consume(KEND, "Expected '}' or 'end' after block.")
  end
  statements
end

#call ⇒ Object 



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# File 'lib/baba/parser.rb', line 317

def call
  expr = primary()

  loop do
    if match(LEFT_PAREN)
      expr = finish_call(expr)
    elsif match(DOT)
      name = consume(IDENTIFIER, "Expected property name '.'.")
      expr = Expr::Get.new(expr, name)
    else
      break
    end
  end

  expr
end

#check(type) ⇒ Object 



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# File 'lib/baba/parser.rb', line 382

def check(type)
  return false if eof?
  peek().type == type
end

#class_declaration ⇒ Object 



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# File 'lib/baba/parser.rb', line 46

def class_declaration
  name = consume(IDENTIFIER, "Expected class name.")

  superclass = if match(LESS)
      consume(IDENTIFIER, "Expected superclass name.")
      Expr::Variable.new(previous())
    end

  consume(COLON, "Expected ':' or '{' before class body.")

  methods = []
  until check(KEND) || eof?
    consume(DOES, "Expected 'does' before method declaration.")
    methods << function("method")
  end

  consume(KEND, "Expected 'end' or '}' after class body.")

  Stmt::Class.new(name, superclass, methods)
end

#comparison ⇒ Object 



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# File 'lib/baba/parser.rb', line 257

def comparison()
  expr = term()

  while match(GREATER, GREATER_EQUAL, LESS, LESS_EQUAL)
    operator = previous()
    right = term()
    expr = Expr::Binary.new(expr, operator, right)
  end

  return expr
end

#consume(type, message) ⇒ Object 



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# File 'lib/baba/parser.rb', line 376

def consume(type, message)
  return advance() if check(type)

  raise(error(peek(), message))
end

#declaration ⇒ Object 



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# File 'lib/baba/parser.rb', line 33

def declaration
  begin
    return class_declaration() if match(THING)
    return function("function") if match(DOES)
    return var_declaration() if match(VAR)

    return statement()
  rescue ParserError => error
    synchronize()
    return nil
  end
end

#eof? ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/baba/parser.rb', line 392

def eof?
  peek().type == EOF
end

#equality ⇒ Object 



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# File 'lib/baba/parser.rb', line 245

def equality()
  expr = comparison()

  while match(NOT_EQUAL, EQUAL_EQUAL)
    operator = previous()
    right = comparison()
    expr = Expr::Binary.new(expr, operator, right)
  end

  return expr
end

#error(token, message) ⇒ Object 



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# File 'lib/baba/parser.rb', line 404

def error(token, message)
  Baba.parser_error(token, message)
  ParserError.new
end

#expr_and ⇒ Object 



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# File 'lib/baba/parser.rb', line 233

def expr_and
  expr = equality()

  while match(AND)
    operator = previous()
    right = equality()
    expr = Expr::Logical.new(expr, operator, right)
  end

  expr
end

#expr_or ⇒ Object 



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# File 'lib/baba/parser.rb', line 221

def expr_or
  expr = expr_and()

  while match(OR)
    operator = previous()
    right = expr_and()
    expr = Expr::Logical.new(expr, operator, right)
  end

  expr
end

#expression ⇒ Object 



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# File 'lib/baba/parser.rb', line 29

def expression
  assignment()
end

#expression_statement ⇒ Object 



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# File 'lib/baba/parser.rb', line 166

def expression_statement
  expr = expression()
  # consume(SEMICOLON, "Expected ';' after expression")
  Stmt::Expression.new(expr)
end

#factor ⇒ Object 



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# File 'lib/baba/parser.rb', line 281

def factor
  expr = unary()

  while match(SLASH, STAR)
    operator = previous()
    right = unary()
    expr = Expr::Binary.new(expr, operator, right)
  end

  return expr
end

#finish_call(callee) ⇒ Object 



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# File 'lib/baba/parser.rb', line 303

def finish_call(callee)
  arguments = []
  unless check(RIGHT_PAREN)
    loop do
      arguments << expression()
      break unless match(COMMA)
    end
  end

  paren = consume(RIGHT_PAREN, "Expected ')' after arguments.")

  Expr::Call.new(callee, paren, arguments)
end

#for_statement ⇒ Object 



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# File 'lib/baba/parser.rb', line 89

def for_statement
  initializer = if check(COMMA)
      nil
    elsif match(VAR)
      var_declaration()
    else
      expression_statement()
    end
  consume(COMMA, "Expected ',' after loop initializer")

  condition = unless check(COMMA)
      expression()
    else
      nil
    end
  consume(COMMA, "Expected ',' after loop condition")

  increment = unless check(COLON)
      expression()
    else
      nil
    end

  body = statement()

  unless increment.nil?
    body = Stmt::Block.new([body, Stmt::Expression.new(increment)])
  end

  if condition.nil?
    condition = Expr::Literal.new(true)
  end

  body = Stmt::While.new(condition, body)

  unless initializer.nil?
    body = Stmt::Block.new([initializer, body])
  end

  body
end

#function(kind) ⇒ Object 



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# File 'lib/baba/parser.rb', line 172

def function(kind)
  name = consume(IDENTIFIER, "Expecteded #{kind} name.")
  consume(LEFT_PAREN, "Expected '(' after #{kind} + name.")
  parameters = []
  unless check(RIGHT_PAREN)
    loop do
      parameters << consume(IDENTIFIER, "Expected parameter name.")
      break unless match(COMMA)
    end
  end
  consume(RIGHT_PAREN, "Expected ')' after parameters.")

  consume(COLON, "Expected ':' or '{' before #{kind} body.")
  body = block()
  Stmt::Function.new(name, parameters, body)
end

#if_statement ⇒ Object 



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# File 'lib/baba/parser.rb', line 131

def if_statement
  condition = expression()

  then_branch = statement()
  else_branch = nil
  else_branch = statement() if match(ELSE)

  return Stmt::If.new(condition, then_branch, else_branch)
end

#match(*types) ⇒ Object 



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# File 'lib/baba/parser.rb', line 365

def match(*types)
  types.each do |type|
    if check(type)
      advance()
      return true
    end
  end

  false
end

#parse ⇒ Object 



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# File 'lib/baba/parser.rb', line 19

def parse
  statements = []

  while !eof?
    statements << declaration()
  end

  statements
end

#peek ⇒ Object 



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# File 'lib/baba/parser.rb', line 396

def peek
  @tokens[@current]
end

#previous ⇒ Object 



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# File 'lib/baba/parser.rb', line 400

def previous
  @tokens[@current - 1]
end

#primary ⇒ Object 



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# File 'lib/baba/parser.rb', line 334

def primary
  return Expr::Literal.new(false) if match(FALSE)
  return Expr::Literal.new(true) if match(TRUE)
  return Expr::Literal.new(nil) if match(BLANK)
  return Expr::Break.new(previous()) if match(BREAK)
  return Expr::Self.new(previous()) if match(SELF)

  if match(NUMBER, STRING)
    return Expr::Literal.new(previous.literal())
  end

  if match(SUPER)
    keyword = previous()
    consume(DOT, "Expected '.' after super.")
    method = consume(IDENTIFIER, "Expected super thing method name.")
    return Expr::Super.new(keyword, method)
  end

  if match(IDENTIFIER)
    return Expr::Variable.new(previous())
  end

  if match(LEFT_PAREN)
    expr = expression()
    consume(RIGHT_PAREN, "Expected ')' after expression.")
    return Expr::Grouping.new(expr)
  end

  raise error(peek(), "Expect expression.")
end

#rb_eval_statement ⇒ Object 



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# File 'lib/baba/parser.rb', line 141

def rb_eval_statement
  value = expression()
  # consume(SEMICOLON, "Expected ';' after value.")
  Stmt::RBEval.new(value)
end

#return_statement ⇒ Object 



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# File 'lib/baba/parser.rb', line 147

def return_statement
  keyword = previous()

  value = if match(SEMICOLON)
      nil
    else
      expression()
    end

  Stmt::Return.new(keyword, value)
end

#statement ⇒ Object 



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# File 'lib/baba/parser.rb', line 77

def statement
  return for_statement() if match(FOR)
  return if_statement() if match(IF)
  return rb_eval_statement() if match(RBEVAL)
  return return_statement() if match(RETURN)
  return while_statement() if match(WHILE)
  return Stmt::Block.new(block()) if match(COLON)
  return Stmt::Include.new(expression()) if match(INCLUDE)

  return expression_statement()
end

#synchronize ⇒ Object 



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# File 'lib/baba/parser.rb', line 411

def synchronize
  advance()
  until eof?
    break if previous().type == SEMICOLON
    break if BREAKING_TOKENS.include?(peek().type)

    advance()
  end
end

#term ⇒ Object 



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# File 'lib/baba/parser.rb', line 269

def term
  expr = factor()

  while match(MINUS, PLUS)
    operator = previous()
    right = factor()
    expr = Expr::Binary.new(expr, operator, right)
  end

  return expr
end

#unary ⇒ Object 



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# File 'lib/baba/parser.rb', line 293

def unary
  if match(NOT, MINUS)
    operator = previous()
    right = unary()
    return Expr::Unary.new(operator, right)
  end

  return call()
end

#var_declaration ⇒ Object 



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# File 'lib/baba/parser.rb', line 67

def var_declaration
  name = consume(IDENTIFIER, "Expected variable name")

  initializer = nil
  initializer = expression() if match(EQUAL)

  # consume(SEMICOLON, "Expected ';' after variable declaration.")
  Stmt::Var.new(name, initializer)
end

#while_statement ⇒ Object 



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# File 'lib/baba/parser.rb', line 159

def while_statement
  condition = expression()
  body = statement()

  return Stmt::While.new(condition, body)
end