require 'scanner'
require 'tokens'
require 'pp'
require 'ast'
# Base-class for all Parsers.
# Defines some common methods for parsing sourcecode.
class ParserBase
include Tokens
include AST
# The constructor takes a Scanner instance as an argument
# to read the source code to parse from.
def initialize(scanner)
@scanner = scanner
end
def zero_or_more(sym)
res = []
while e = send(("parse_"+sym.to_s).to_sym); res << e; end
res
end
def position
@scanner.position
end
def expect(*args)
args.each do |a|
r = @scanner.expect(a)
return r if r
end
return nil
end
def expected(name)
error("Expected: #{name}")
end
def nolfws
@scanner.nolfws
end
def ws
@scanner.ws
end
# Returns filename from which parser reads code.
def filename
@scanner.filename
end
# Returns true, if the parser gets code from a file.
def from_file?
!@scanner.filename.nil?
end
# Output error message by raising an exception.
# Error message contains filename and linenumber, if reading from a file.
# Otherwise, the message only contains the current linenumber and the error message.
def error(message)
if from_file?
raise "Parse error: #{filename}(#{@scanner.lineno}): #{message}"
else
raise "Parse error: #{@scanner.lineno}: #{message}"
end
end
protected
# Protected accessor method for the scanner object.
# For use in subclasses.
def scanner
@scanner
end
end
