#!/usr/bin/ruby
# encoding: utf-8
=begin LICENSE
[The "BSD licence"]
Copyright (c) 2009-2010 Kyle Yetter
All rights reserved.
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:
1. Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
2. Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in the
documentation and/or other materials provided with the distribution.
3. The name of the author may not be used to endorse or promote products
derived from this software without specific prior written permission.
THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
=end
module ANTLR3
unless const_defined?( :RecognizerSharedState )
RecognizerSharedState = Struct.new(
:following,
:error_recovery,
:last_error_index,
:backtracking,
:rule_memory,
:syntax_errors,
:token,
:token_start_position,
:token_start_line,
:token_start_column,
:channel,
:type,
:text
)
=begin rdoc ANTLR3::RecognizerSharedState
A big Struct-based class containing most of the data that makes up a
recognizer's state. These attributes are externalized from the recognizer itself
so that recognizer delegation (which occurs when you import other grammars into
your grammar) can function; multiple recognizers can share a common state.
== Structure Attributes
following::
a stack that tracks follow sets for error recovery
error_recovery::
a flag indicating whether or not the recognizer is in error recovery mode
last_error_index::
the index in the input stream of the last error
backtracking::
tracks the backtracking depth
rule_memory::
if a grammar is compiled with the memoization option, this will be
set to a hash mapping previously parsed rules to cached indices
syntax_errors::
tracks the number of syntax errors seen so far
token::
holds newly constructed tokens for lexer rules
token_start_position::
the input stream index at which the token starts
token_start_line::
the input stream line number at which the token starts
token_start_column::
the input stream column at which the token starts
channel::
the channel value of the target token
type::
the type value of the target token
text::
the text of the target token
=end
class RecognizerSharedState
def initialize
super( [], false, -1, 0, nil, 0, nil, -1 )
# ^-- same as this --v
# self.following = []
# self.error_recovery = false
# self.last_error_index = -1
# self.backtracking = 0
# self.syntax_errors = 0
# self.token_start_position = -1
end
# restores all of the state variables to their respective
# initial default values
def reset!
self.following.clear
self.error_recovery = false
self.last_error_index = -1
self.backtracking = 0
self.rule_memory and rule_memory.clear
self.syntax_errors = 0
self.token = nil
self.token_start_position = -1
self.token_start_line = nil
self.token_start_column = nil
self.channel = nil
self.type = nil
self.text = nil
end
end
end # unless const_defined?( :RecognizerSharedState )
=begin rdoc ANTLR3::Recognizer
= Scope
Scope is used to represent instances of ANTLR's various attribute scopes.
It is identical to Ruby's built-in Struct class, but it takes string
attribute declarations from the ANTLR grammar as parameters, and overrides
the #initialize method to set the default values if any are present in
the scope declaration.
Block = Scope.new( "name", "depth = 0", "variables = {}" )
Block.new # => #<struct Block name=nil, depth=0, variables={}>
Block.new( "function" ) # => #<struct Block name="function", depth=0, variables={}>
Block.new( 'a', 1, :x => 3 ) # => #<struct Block name="a", depth=1, variables={ :x => 3 }>
=end
class Scope < ::Struct
def self.new( *declarations, &body )
names = []
defaults = {}
for decl in declarations
name, default = decl.to_s.split( /\s*=\s*/, 2 )
names << ( name = name.to_sym )
default and defaults[ name ] = default
end
super( *names ) do
# If no defaults, leave the initialize method the same as
# the struct's default initialize for speed. Otherwise,
# overwrite the initialize to populate with default values.
unless defaults.empty?
parameters = names.map do | name |
"#{ name } = " << defaults.fetch( name, 'nil' )
end.join( ', ' )
class_eval( <<-END )
def initialize( #{ parameters } )
super( #{ names.join( ', ' ) } )
end
END
end
body and class_eval( &body )
end
end
end
=begin rdoc ANTLR3::Recognizer
= Recognizer
As the base class of all ANTLR-generated recognizers, Recognizer provides
much of the shared functionality and structure used in the recognition process.
For all effective purposes, the class and its immediate subclasses Lexer,
Parser, and TreeParser are abstract classes. They can be instantiated, but
they're pretty useless on their own. Instead, to make useful code, you write an
ANTLR grammar and ANTLR will generate classes which inherit from one of the
recognizer base classes, providing the implementation of the grammar rules
itself. this group of classes to implement necessary tasks. Recognizer
defines methods related to:
* token and character matching
* prediction and recognition strategy
* recovering from errors
* reporting errors
* memoization
* simple rule tracing and debugging
=end
class Recognizer
include Constants
include Error
include TokenFactory
extend ClassMacros
@rules = {}
# inherited class methods and hooks
class << self
attr_reader :grammar_file_name,
:antlr_version,
:antlr_version_string,
:library_version_string,
:grammar_home
attr_accessor :token_scheme, :default_rule
# generated recognizer code uses this method to stamp
# the code with the name of the grammar file and
# the current version of ANTLR being used to generate
# the code
def generated_using( grammar_file, antlr_version, library_version = nil )
@grammar_file_name = grammar_file.freeze
@antlr_version_string = antlr_version.freeze
@library_version = Util.parse_version( library_version )
if @antlr_version_string =~ /^(\d+)\.(\d+)(?:\.(\d+)(?:b(\d+))?)?(.*)$/
@antlr_version = [ $1, $2, $3, $4 ].map! { |str| str.to_i }
timestamp = $5.strip
#@antlr_release_time = $5.empty? ? nil : Time.parse($5)
else
raise "bad version string: %p" % version_string
end
end
# this method is used to generate return-value structures for
# rules with multiple return values. To avoid generating
# a special class for ever rule in AST parsers and such
# (where most rules have the same default set of return values),
# each recognizer gets a default return value structure
# assigned to the constant +Return+. Rules which don't
# require additional custom members will have a rule-return
# name constant that just points to the generic return
# value.
def define_return_scope( *members )
if members.empty? then generic_return_scope
else
members += return_scope_members
Struct.new( *members )
end
end
# used as a hook to add additional default members
# to default return value structures
# For example, all AST-building parsers override
# this method to add an extra +:tree+ field to
# all rule return structures.
def return_scope_members
[ :start, :stop ]
end
# sets up and returns the generic rule return
# scope for a recognizer
def generic_return_scope
@generic_return_scope ||= begin
struct = Struct.new( *return_scope_members )
const_set( :Return, struct )
end
end
def imported_grammars
@imported_grammars ||= Set.new
end
def master_grammars
@master_grammars ||= []
end
def master
master_grammars.last
end
def masters( *grammar_names )
for grammar in grammar_names
unless master_grammars.include?( grammar )
master_grammars << grammar
attr_reader( Util.snake_case( grammar ) )
end
end
end
private :masters
def imports( *grammar_names )
for grammar in grammar_names
imported_grammars.add?( grammar.to_sym ) and
attr_reader( Util.snake_case( grammar ) )
end
return imported_grammars
end
private :imports
def rules
self::RULE_METHODS.dup rescue []
end
def default_rule
@default_rule ||= rules.first
end
def debug?
return false
end
def profile?
return false
end
def Scope( *declarations, &body )
Scope.new( *declarations, &body )
end
def token_class
@token_class ||= begin
self::Token rescue
superclass.token_class rescue
ANTLR3::CommonToken
end
end
private :generated_using
end
@grammar_file_name = nil
@antlr_version = ANTLR3::ANTLR_VERSION
@antlr_version_string = ANTLR3::ANTLR_VERSION_STRING
def grammar_file_name
self.class.grammar_file_name
end
def antlr_version
self.class.antlr_version
end
def antlr_version_string
self.class.antlr_version_string
end
attr_accessor :input
attr_reader :state
def each_delegate
block_given? or return enum_for( __method__ )
for grammar in self.class.imported_grammars
del = __send__( Util.snake_case( grammar ) ) and
yield( del )
end
end
# Create a new recognizer. The constructor simply ensures that
# all recognizers are initialized with a shared state object.
# See the main recognizer subclasses for more specific
# information about creating recognizer objects like
# lexers and parsers.
def initialize( options = {} )
@state = options[ :state ] || RecognizerSharedState.new
@error_output = options.fetch( :error_output, $stderr )
defined?( @input ) or @input = nil
initialize_dfas
end
# Resets the recognizer's state data to initial values.
# As a result, all error tracking and error recovery
# data accumulated in the current state will be cleared.
# It will also attempt to reset the input stream
# via input.reset, but it ignores any errors received
# from doing so. Thus the input stream is not guarenteed
# to be rewound to its initial position
def reset
@state and @state.reset!
@input and @input.reset rescue nil
end
# Attempt to match the current input symbol the token type
# specified by +type+. If the symbol matches the type,
# consume the current symbol and return its value. If
# the symbol doesn't match, attempt to use the follow-set
# data provided by +follow+ to recover from the mismatched
# token.
def match( type, follow )
matched_symbol = current_symbol
if @input.peek == type
@input.consume
@state.error_recovery = false
return matched_symbol
end
raise( BacktrackingFailed ) if @state.backtracking > 0
return recover_from_mismatched_token( type, follow )
end
# match anything -- i.e. wildcard match. Simply consume
# the current symbol from the input stream.
def match_any
@state.error_recovery = false
@input.consume
end
##############################################################################################
###################################### Error Reporting #######################################
##############################################################################################
##############################################################################################
# When a recognition error occurs, this method is the main
# hook for carrying out the error reporting process. The
# default implementation calls +display_recognition_error+
# to display the error info on $stderr.
def report_error( e = $! )
@state.error_recovery and return
@state.syntax_errors += 1
@state.error_recovery = true
display_recognition_error( e )
end
# error reporting hook for presenting the information
# The default implementation builds appropriate error
# message text using +error_header+ and +error_message+,
# and calls +emit_error_message+ to write the error
# message out to some source
def display_recognition_error( e = $! )
header = error_header( e )
message = error_message( e )
emit_error_message( "#{ header } #{ message }" )
end
# used to construct an appropriate error message
# based on the specific type of error and the
# error's attributes
def error_message( e = $! )
case e
when UnwantedToken
token_name = token_name( e.expecting )
"extraneous input #{ token_error_display( e.unexpected_token ) } expecting #{ token_name }"
when MissingToken
token_name = token_name( e.expecting )
"missing #{ token_name } at #{ token_error_display( e.symbol ) }"
when MismatchedToken
token_name = token_name( e.expecting )
"mismatched input #{ token_error_display( e.symbol ) } expecting #{ token_name }"
when MismatchedTreeNode
token_name = token_name( e.expecting )
"mismatched tree node: #{ e.symbol } expecting #{ token_name }"
when NoViableAlternative
"no viable alternative at input " << token_error_display( e.symbol )
when MismatchedSet
"mismatched input %s expecting set %s" %
[ token_error_display( e.symbol ), e.expecting.inspect ]
when MismatchedNotSet
"mismatched input %s expecting set %s" %
[ token_error_display( e.symbol ), e.expecting.inspect ]
when FailedPredicate
"rule %s failed predicate: { %s }?" % [ e.rule_name, e.predicate_text ]
else e.message
end
end
#
# used to add a tag to the error message that indicates
# the location of the input stream when the error
# occurred
#
def error_header( e = $! )
e.location
end
#
# formats a token object appropriately for inspection
# within an error message
#
def token_error_display( token )
unless text = token.text || ( token.source_text rescue nil )
text =
case
when token.type == EOF then '<EOF>'
when name = token_name( token.type ) rescue nil then "<#{ name }>"
when token.respond_to?( :name ) then "<#{ token.name }>"
else "<#{ token.type }>"
end
end
return text.inspect
end
#
# Write the error report data out to some source. By default,
# the error message is written to $stderr
#
def emit_error_message( message )
@error_output.puts( message ) if @error_output
end
##############################################################################################
###################################### Error Recovery ########################################
##############################################################################################
def recover( error = $! )
@state.last_error_index == @input.index and @input.consume
@state.last_error_index = @input.index
follow_set = compute_error_recovery_set
resync { consume_until( follow_set ) }
end
def resync
begin_resync
return( yield )
ensure
end_resync
end
# overridable hook method that is executed at the start of the
# resyncing procedure in recover
#
# by default, it does nothing
def begin_resync
# do nothing
end
# overridable hook method that is after the resyncing procedure has completed
#
# by default, it does nothing
def end_resync
# do nothing
end
# (The following explanation has been lifted directly from the
# source code documentation of the ANTLR Java runtime library)
#
# Compute the error recovery set for the current rule. During
# rule invocation, the parser pushes the set of tokens that can
# follow that rule reference on the stack; this amounts to
# computing FIRST of what follows the rule reference in the
# enclosing rule. This local follow set only includes tokens
# from within the rule; i.e., the FIRST computation done by
# ANTLR stops at the end of a rule.
#
# EXAMPLE
#
# When you find a "no viable alt exception", the input is not
# consistent with any of the alternatives for rule r. The best
# thing to do is to consume tokens until you see something that
# can legally follow a call to r *or* any rule that called r.
# You don't want the exact set of viable next tokens because the
# input might just be missing a token--you might consume the
# rest of the input looking for one of the missing tokens.
#
# Consider grammar:
#
# a : '[' b ']'
# | '(' b ')'
# ;
# b : c '^' INT ;
# c : ID
# | INT
# ;
#
# At each rule invocation, the set of tokens that could follow
# that rule is pushed on a stack. Here are the various "local"
# follow sets:
#
# FOLLOW( b1_in_a ) = FIRST( ']' ) = ']'
# FOLLOW( b2_in_a ) = FIRST( ')' ) = ')'
# FOLLOW( c_in_b ) = FIRST( '^' ) = '^'
#
# Upon erroneous input "[]", the call chain is
#
# a -> b -> c
#
# and, hence, the follow context stack is:
#
# depth local follow set after call to rule
# 0 \<EOF> a (from main( ) )
# 1 ']' b
# 3 '^' c
#
# Notice that <tt>')'</tt> is not included, because b would have to have
# been called from a different context in rule a for ')' to be
# included.
#
# For error recovery, we cannot consider FOLLOW(c)
# (context-sensitive or otherwise). We need the combined set of
# all context-sensitive FOLLOW sets--the set of all tokens that
# could follow any reference in the call chain. We need to
# resync to one of those tokens. Note that FOLLOW(c)='^' and if
# we resync'd to that token, we'd consume until EOF. We need to
# sync to context-sensitive FOLLOWs for a, b, and c: {']','^'}.
# In this case, for input "[]", LA(1) is in this set so we would
# not consume anything and after printing an error rule c would
# return normally. It would not find the required '^' though.
# At this point, it gets a mismatched token error and throws an
# exception (since LA(1) is not in the viable following token
# set). The rule exception handler tries to recover, but finds
# the same recovery set and doesn't consume anything. Rule b
# exits normally returning to rule a. Now it finds the ']' (and
# with the successful match exits errorRecovery mode).
#
# So, you cna see that the parser walks up call chain looking
# for the token that was a member of the recovery set.
#
# Errors are not generated in errorRecovery mode.
#
# ANTLR's error recovery mechanism is based upon original ideas:
#
# "Algorithms + Data Structures = Programs" by Niklaus Wirth
#
# and
#
# "A note on error recovery in recursive descent parsers":
# http://portal.acm.org/citation.cfm?id=947902.947905
#
# Later, Josef Grosch had some good ideas:
#
# "Efficient and Comfortable Error Recovery in Recursive Descent
# Parsers":
# ftp://www.cocolab.com/products/cocktail/doca4.ps/ell.ps.zip
#
# Like Grosch I implemented local FOLLOW sets that are combined
# at run-time upon error to avoid overhead during parsing.
def compute_error_recovery_set
combine_follows( false )
end
def recover_from_mismatched_token( type, follow )
if mismatch_is_unwanted_token?( type )
err = UnwantedToken( type )
resync { @input.consume }
report_error( err )
return @input.consume
end
if mismatch_is_missing_token?( follow )
inserted = missing_symbol( nil, type, follow )
report_error( MissingToken( type, inserted ) )
return inserted
end
raise MismatchedToken( type )
end
def recover_from_mismatched_set( e, follow )
if mismatch_is_missing_token?( follow )
report_error( e )
return missing_symbol( e, INVALID_TOKEN_TYPE, follow )
end
raise e
end
def recover_from_mismatched_element( e, follow )
follow.nil? and return false
if follow.include?( EOR_TOKEN_TYPE )
viable_tokens = compute_context_sensitive_rule_follow
follow = ( follow | viable_tokens ) - Set[ EOR_TOKEN_TYPE ]
end
if follow.include?( @input.peek )
report_error( e )
return true
end
return false
end
# Conjure up a missing token during error recovery.
#
# The recognizer attempts to recover from single missing
# symbols. But, actions might refer to that missing symbol.
# For example, x=ID {f($x);}. The action clearly assumes
# that there has been an identifier matched previously and that
# $x points at that token. If that token is missing, but
# the next token in the stream is what we want we assume that
# this token is missing and we keep going. Because we
# have to return some token to replace the missing token,
# we have to conjure one up. This method gives the user control
# over the tokens returned for missing tokens. Mostly,
# you will want to create something special for identifier
# tokens. For literals such as '{' and ',', the default
# action in the parser or tree parser works. It simply creates
# a CommonToken of the appropriate type. The text will be the token.
# If you change what tokens must be created by the lexer,
# override this method to create the appropriate tokens.
def missing_symbol( error, expected_token_type, follow )
return nil
end
def mismatch_is_unwanted_token?( type )
@input.peek( 2 ) == type
end
def mismatch_is_missing_token?( follow )
follow.nil? and return false
if follow.include?( EOR_TOKEN_TYPE )
viable_tokens = compute_context_sensitive_rule_follow
follow = follow | viable_tokens
follow.delete( EOR_TOKEN_TYPE ) unless @state.following.empty?
end
if follow.include?( @input.peek ) or follow.include?( EOR_TOKEN_TYPE )
return true
end
return false
end
def syntax_errors?
( error_count = @state.syntax_errors ) > 0 and return( error_count )
end
# factor out what to do upon token mismatch so
# tree parsers can behave differently.
#
# * override this method in your parser to do things
# like bailing out after the first error
# * just raise the exception instead of
# calling the recovery method.
#
def number_of_syntax_errors
@state.syntax_errors
end
#
# Compute the context-sensitive +FOLLOW+ set for current rule.
# This is set of token types that can follow a specific rule
# reference given a specific call chain. You get the set of
# viable tokens that can possibly come next (look depth 1)
# given the current call chain. Contrast this with the
# definition of plain FOLLOW for rule r:
#
# FOLLOW(r)={x | S=>*alpha r beta in G and x in FIRST(beta)}
#
# where x in T* and alpha, beta in V*; T is set of terminals and
# V is the set of terminals and nonterminals. In other words,
# FOLLOW(r) is the set of all tokens that can possibly follow
# references to r in *any* sentential form (context). At
# runtime, however, we know precisely which context applies as
# we have the call chain. We may compute the exact (rather
# than covering superset) set of following tokens.
#
# For example, consider grammar:
#
# stat : ID '=' expr ';' // FOLLOW(stat)=={EOF}
# | "return" expr '.'
# ;
# expr : atom ('+' atom)* ; // FOLLOW(expr)=={';','.',')'}
# atom : INT // FOLLOW(atom)=={'+',')',';','.'}
# | '(' expr ')'
# ;
#
# The FOLLOW sets are all inclusive whereas context-sensitive
# FOLLOW sets are precisely what could follow a rule reference.
# For input input "i=(3);", here is the derivation:
#
# stat => ID '=' expr ';'
# => ID '=' atom ('+' atom)* ';'
# => ID '=' '(' expr ')' ('+' atom)* ';'
# => ID '=' '(' atom ')' ('+' atom)* ';'
# => ID '=' '(' INT ')' ('+' atom)* ';'
# => ID '=' '(' INT ')' ';'
#
# At the "3" token, you'd have a call chain of
#
# stat -> expr -> atom -> expr -> atom
#
# What can follow that specific nested ref to atom? Exactly ')'
# as you can see by looking at the derivation of this specific
# input. Contrast this with the FOLLOW(atom)={'+',')',';','.'}.
#
# You want the exact viable token set when recovering from a
# token mismatch. Upon token mismatch, if LA(1) is member of
# the viable next token set, then you know there is most likely
# a missing token in the input stream. "Insert" one by just not
# throwing an exception.
#
def compute_context_sensitive_rule_follow
combine_follows true
end
def combine_follows( exact )
follow_set = Set.new
@state.following.each_with_index.reverse_each do |local_follow_set, index|
follow_set |= local_follow_set
if exact
if local_follow_set.include?( EOR_TOKEN_TYPE )
follow_set.delete( EOR_TOKEN_TYPE ) if index > 0
else
break
end
end
end
return follow_set
end
#
# Match needs to return the current input symbol, which gets put
# into the label for the associated token ref; e.g., x=ID. Token
# and tree parsers need to return different objects. Rather than test
# for input stream type or change the IntStream interface, I use
# a simple method to ask the recognizer to tell me what the current
# input symbol is.
#
# This is ignored for lexers.
#
def current_symbol
@input.look
end
#
# Consume input symbols until one matches a type within types
#
# types can be a single symbol type or a set of symbol types
#
def consume_until( types )
types.is_a?( Set ) or types = Set[ *types ]
type = @input.peek
until type == EOF or types.include?( type )
@input.consume
type = @input.peek
end
return( type )
end
#
# Returns true if the recognizer is currently in a decision for which
# backtracking has been enabled
#
def backtracking?
@state.backtracking > 0
end
def backtracking_level
@state.backtracking
end
def backtracking_level=( n )
@state.backtracking = n
end
def backtrack
@state.backtracking += 1
start = @input.mark
success =
begin yield
rescue BacktrackingFailed then false
else true
end
return success
ensure
@input.rewind( start )
@state.backtracking -= 1
end
def syntactic_predicate?( name )
backtrack { send name }
end
alias backtracking backtracking_level
alias backtracking= backtracking_level=
def rule_memoization( rule, start_index )
@state.rule_memory.fetch( rule ) do
@state.rule_memory[ rule ] = Hash.new( MEMO_RULE_UNKNOWN )
end[ start_index ]
end
def already_parsed_rule?( rule )
stop_index = rule_memoization( rule, @input.index )
case stop_index
when MEMO_RULE_UNKNOWN then return false
when MEMO_RULE_FAILED
raise BacktrackingFailed
else
@input.seek( stop_index + 1 )
end
return true
end
def memoize( rule, start_index, success )
stop_index = success ? @input.index - 1 : MEMO_RULE_FAILED
memo = @state.rule_memory[ rule ] and memo[ start_index ] = stop_index
end
def trace_in( rule_name, rule_index, input_symbol )
@error_output.printf( "--> enter %s on %s", rule_name, input_symbol )
@state.backtracking > 0 and @error_output.printf(
" (in backtracking mode: depth = %s)", @state.backtracking
)
@error_output.print( "\n" )
end
def trace_out( rule_name, rule_index, input_symbol )
@error_output.printf( "<-- exit %s on %s", rule_name, input_symbol )
@state.backtracking > 0 and @error_output.printf(
" (in backtracking mode: depth = %s)", @state.backtracking
)
@error_output.print( "\n" )
end
private
def initialize_dfas
# do nothing
end
end
# constant alias for compatibility with older versions of the
# runtime library
BaseRecognizer = Recognizer
=begin rdoc ANTLR3::Lexer
= Lexer
Lexer is the default superclass of all lexers generated by ANTLR. The class
tailors the core functionality provided by Recognizer to the task of
matching patterns in the text input and breaking the input into tokens.
== About Lexers
A lexer's job is to take input text and break it up into _tokens_ -- objects
that encapsulate a piece of text, a type label (such as ID or INTEGER), and the
position of the text with respect to the input. Thus, a lexer is essentially a
complicated iterator that steps through an input stream and produces a sequence
of tokens. Sometimes lexers are enough to carry out a goal on their own, such as
tasks like source code highlighting and simple code analysis. Usually, however,
the lexer converts text into tokens for use by a parser, which recognizes larger
structures within the text.
ANTLR parsers have a variety of entry points specified by parser rules, each of
which defines the structure of a specific type of sentence in a grammar. Lexers,
however, are primarily intended to have a single entry point. It looks at the
characters starting at the current input position, decides if the chunk of text
matches one of a number of possible token type definitions, wraps the chunk into
a token with information on its type and location, and advances the input stream
to the next place.
== ANTLR Lexers and the Lexer API
ANTLR-generated lexers will subclass this class, unless specified otherwise
within a grammar file. The generated class will provide an implementation of
each lexer rule as a method of the same name. The subclass will also provide an
implementation for the abstract method #m_tokens, the purpose of which is to
multiplex the token type definitions and predict what rule definition to execute
to fetch a token. The primary method in the lexer API, #next_token, uses
#m_tokens to fetch the next token and drive the iteration.
If the lexer is preparing tokens for use by an ANTLR generated parser, the lexer
will generally be used to build a TokenStream object. The following code example
demonstrates the typical setup for using ANTLR parsers and lexers in Ruby.
# in HypotheticalLexer.rb
module Hypothetical
class Lexer < ANTLR3::Lexer
# ...
# ANTLR generated code
# ...
end
end
# in HypotheticalParser.rb
module Hypothetical
class Parser < ANTLR3::Parser
# ...
# more ANTLR generated code
# ...
end
end
# to take hypothetical source code and prepare it for parsing,
# there is generally a four-step construction process
source = "some hypothetical source code"
input = ANTLR3::StringStream.new(source, :file => 'blah-de-blah.hyp')
lexer = Hypothetical::Lexer.new( input )
tokens = ANTLR3::CommonTokenStream.new( lexer )
parser = Hypothetical::Parser.new( tokens )
# if you're using the standard streams, ANTLR3::StringStream and
# ANTLR3::CommonTokenStream, you can write the same process
# shown above more succinctly:
lexer = Hypothetical::Lexer.new("some hypothetical source code", :file => 'blah-de-blah.hyp')
parser = Hypothetical::Parser.new( lexer )
=end
class Lexer < Recognizer
include TokenSource
@token_class = CommonToken
def self.default_rule
@default_rule ||= :token!
end
def self.main( argv = ARGV, options = {} )
if argv.is_a?( ::Hash ) then argv, options = ARGV, argv end
main = ANTLR3::Main::LexerMain.new( self, options )
block_given? ? yield( main ) : main.execute( argv )
end
def self.associated_parser
@associated_parser ||= begin
@grammar_home and @grammar_home::Parser
rescue NameError
grammar_name = @grammar_home.name.split( "::" ).last
begin
require "#{ grammar_name }Parser"
@grammar_home::Parser
rescue LoadError, NameError
end
end
end
def initialize( input, options = {} )
super( options )
@input = cast_input( input, options )
end
def current_symbol
nil
end
def next_token
loop do
@state.token = nil
@state.channel = DEFAULT_CHANNEL
@state.token_start_position = @input.index
@state.token_start_column = @input.column
@state.token_start_line = @input.line
@state.text = nil
@input.peek == EOF and return EOF_TOKEN
begin
token!
case token = @state.token
when nil then return( emit )
when SKIP_TOKEN then next
else
return token
end
rescue NoViableAlternative => re
report_error( re )
recover( re )
rescue Error::RecognitionError => re
report_error( re )
end
end
end
def skip
@state.token = SKIP_TOKEN
end
abstract :token!
def exhaust
self.to_a
end
def char_stream=( input )
@input = nil
reset()
@input = input
end
def source_name
@input.source_name
end
def emit( token = @state.token )
token ||= create_token
@state.token = token
return token
end
def match( expected )
case expected
when String
expected.each_byte do |char|
unless @input.peek == char
@state.backtracking > 0 and raise BacktrackingFailed
error = MismatchedToken( char )
recover( error )
raise error
end
@input.consume()
end
else # single integer character
unless @input.peek == expected
@state.backtracking > 0 and raise BacktrackingFailed
error = MismatchedToken( expected )
recover( error )
raise error
end
@input.consume
end
return true
end
def match_any
@input.consume
end
def match_range( min, max )
char = @input.peek
if char.between?( min, max ) then @input.consume
else
@state.backtracking > 0 and raise BacktrackingFailed
error = MismatchedRange( min.chr, max.chr )
recover( error )
raise( error )
end
return true
end
def line
@input.line
end
def column
@input.column
end
def character_index
@input.index
end
def text
@state.text and return @state.text
@input.substring( @state.token_start_position, character_index - 1 )
end
def text=( text )
@state.text = text
end
def report_error( e )
display_recognition_error( e )
end
def error_message( e )
char = character_error_display( e.symbol ) rescue nil
case e
when Error::MismatchedToken
expecting = character_error_display( e.expecting )
"mismatched character #{ char }; expecting #{ expecting }"
when Error::NoViableAlternative
"no viable alternative at character #{ char }"
when Error::EarlyExit
"required ( ... )+ loop did not match anything at character #{ char }"
when Error::MismatchedNotSet
"mismatched character %s; expecting set %p" % [ char, e.expecting ]
when Error::MismatchedSet
"mismatched character %s; expecting set %p" % [ char, e.expecting ]
when Error::MismatchedRange
a = character_error_display( e.min )
b = character_error_display( e.max )
"mismatched character %s; expecting set %s..%s" % [ char, a, b ]
else super
end
end
def character_error_display( char )
case char
when EOF then '<EOF>'
when Integer then char.chr.inspect
else char.inspect
end
end
def recover( re )
@input.consume
end
alias input= char_stream=
private
def cast_input( input, options )
case input
when CharacterStream then input
when ::String then StringStream.new( input, options )
when ::IO, ARGF then FileStream.new( input, options )
else input
end
end
def trace_in( rule_name, rule_index )
if symbol = @input.look and symbol != EOF then symbol = symbol.inspect
else symbol = '<EOF>' end
input_symbol = "#{ symbol } @ line #{ line } / col #{ column }"
super( rule_name, rule_index, input_symbol )
end
def trace_out( rule_name, rule_index )
if symbol = @input.look and symbol != EOF then symbol = symbol.inspect
else symbol = '<EOF>' end
input_symbol = "#{ symbol } @ line #{ line } / col #{ column }"
super( rule_name, rule_index, input_symbol )
end
def create_token( &b )
if block_given? then super( &b )
else
super do |t|
t.input = @input
t.type = @state.type
t.channel = @state.channel
t.start = @state.token_start_position
t.stop = @input.index - 1
t.line = @state.token_start_line
t.text = self.text
t.column = @state.token_start_column
end
end
end
end
=begin rdoc ANTLR3::Parser
= Parser
Parser is the default base class of ANTLR-generated parser classes. The class
tailors the functionality provided by Recognizer to the task of parsing.
== About Parsing
This is just a lose overview of parsing. For considerably more in-depth coverage
of the topic, read the ANTLR documentation or check out the ANTLR website
(http://www.antlr.org).
A grammar defines the vocabulary and the sentence structure of a language. While
a lexer concerns the basic vocabulary symbols of the language, a parser's
primary task is to implement the sentence structure.
Parsers are set up by providing a stream of tokens, which is usually created by
a corresponding lexer. Then, the user requests a specific sentence-structure
within the grammar, such as "class_definition" or "xml_node", from the parser.
It iterates through the tokens, verifying the syntax of the sentence and
performing actions specified by the grammar. It stops when it encounters an
error or when it has matched the full sentence according to its defined
structure.
== ANTLR Parsers and the Parser API
Plain ANTLR-generated parsers directly subclass this class, unless specified
otherwise within the grammar options. The generated code will provide a method
for each parser rule defined in the ANTLR grammar, as well as any other
customized member attributes and methods specified in the source grammar.
This class does not override much of the functionality in Recognizer, and
thus the API closely mirrors Recognizer.
=end
class Parser < Recognizer
def self.main( argv = ARGV, options = {} )
if argv.is_a?( ::Hash ) then argv, options = ARGV, argv end
main = ANTLR3::Main::ParserMain.new( self, options )
block_given? ? yield( main ) : main.execute( argv )
end
def self.associated_lexer
@associated_lexer ||= begin
@grammar_home and @grammar_home::Lexer
rescue NameError
grammar_name = @grammar_home.name.split( "::" ).last
begin
require "#{ grammar_name }Lexer"
@grammar_home::Lexer
rescue LoadError, NameError
end
end
end
def initialize( input, options = {} )
super( options )
@input = nil
reset
@input = cast_input( input, options )
end
def missing_symbol( error, expected_type, follow )
current = @input.look
current = @input.look( -1 ) if current == ANTLR3::EOF_TOKEN
t =
case
when current && current != ANTLR3::EOF_TOKEN then current.clone
when @input.token_class then @input.token_class.new
else ( create_token rescue CommonToken.new )
end
t.type = expected_type
name = t.name.gsub( /(^<)|(>$)/,'' )
t.text = "<missing #{ name }>"
t.channel = DEFAULT_CHANNEL
return( t )
end
def token_stream=( input )
@input = nil
reset
@input = input
end
alias token_stream input
def source_name
@input.source_name
end
private
def trace_in( rule_name, rule_index )
super( rule_name, rule_index, @input.look.inspect )
end
def trace_out( rule_name, rule_index )
super( rule_name, rule_index, @input.look.inspect )
end
def cast_input( input, options )
case input
when TokenStream then input
when TokenSource then CommonTokenStream.new( input, options )
when IO, String, CharacterStream
if lexer_class = self.class.associated_lexer
CommonTokenStream.new( lexer_class.new( input, options ), options )
else
raise ArgumentError, Util.tidy( <<-END, true )
| unable to automatically convert input #{ input.inspect }
| to a ANTLR3::TokenStream object as #{ self.class }
| does not appear to have an associated lexer class
END
end
else
# assume it's a stream if it at least implements peek and consume
unless input.respond_to?( :peek ) and input.respond_to?( :consume )
raise ArgumentError, Util.tidy( <<-END, true )
| #{ self.class } requires a token stream as input, but
| #{ input.inspect } was provided
END
end
input
end
end
end
end