Class: Platform::IEL::SexpParser

Inherits:
Object
  • Object
show all
Defined in:
lib/introhive_expression_language/iel/sexp_parser.rb

Defined Under Namespace

Classes: Lexer, Node, ParseContext, ParseError, UnexpectedTokenError

Class Method Summary collapse

Class Method Details

.parse(expr) ⇒ Object

Parse the given expression and return its AST. Raises SexpParser::ParseError if a syntax error is encountered.



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# File 'lib/introhive_expression_language/iel/sexp_parser.rb', line 20

def self.parse(expr)
  parse_context = ParseContext.new(expr)
  node_stack = [Node.new(:list, 0, [], parse_context)]
  Lexer.tokenize(expr.chars, 0, parse_context) do |token|
    case token.kind
    when :string_literal, :numeric_literal, :symbol, :boolean, :nan, :nil
      node_stack.last.value << token
    when :list_end
      raise UnexpectedTokenError, token if node_stack.size == 1
      value = node_stack.pop
      raise UnexpectedTokenError, token if value.nil?
      node_stack.last.value << value
    when :list_start
      node_stack.push(Node.new(:list, token.source, [], parse_context))
    when :comment
      # Do nothing
    else
      raise UnexpectedTokenError, token
    end
  end
  if node_stack.size != 1
    raise ParseError, 'Unexpected end of input'
  end

  # Remove containing list if there's only a single item results.
  if node_stack.first.value.size == 1
    node_stack = node_stack.first.value
  end

  node_stack.first
end