org.antlr.runtime
Class BaseRecognizer
java.lang.Object
org.antlr.runtime.BaseRecognizer
- Direct Known Subclasses:
- Lexer, Parser, TreeParser
public abstract class BaseRecognizer
- extends java.lang.Object
A generic recognizer that can handle recognizers generated from
lexer, parser, and tree grammars. This is all the parsing
support code essentially; most of it is error recovery stuff and
backtracking.
Method Summary |
boolean |
alreadyParsedRule(IntStream input,
int ruleIndex)
Has this rule already parsed input at the current index in the
input stream? Return the stop token index or MEMO_RULE_UNKNOWN. |
void |
beginResync()
A hook to listen in on the token consumption during error recovery. |
protected BitSet |
combineFollows(boolean exact)
|
protected BitSet |
computeContextSensitiveRuleFOLLOW()
Compute the context-sensitive FOLLOW set for current rule. |
protected BitSet |
computeErrorRecoverySet()
|
void |
consumeUntil(IntStream input,
BitSet set)
Consume tokens until one matches the given token set |
void |
consumeUntil(IntStream input,
int tokenType)
|
void |
displayRecognitionError(java.lang.String[] tokenNames,
RecognitionException e)
|
void |
emitErrorMessage(java.lang.String msg)
Override this method to change where error messages go |
void |
endResync()
|
boolean |
failed()
Return whether or not a backtracking attempt failed. |
int |
getBacktrackingLevel()
|
protected java.lang.Object |
getCurrentInputSymbol(IntStream input)
Match needs to return the current input symbol, which gets put
into the label for the associated token ref; e.g., x=ID. |
java.lang.String |
getErrorHeader(RecognitionException e)
What is the error header, normally line/character position information? |
java.lang.String |
getErrorMessage(RecognitionException e,
java.lang.String[] tokenNames)
What error message should be generated for the various
exception types?
Not very object-oriented code, but I like having all error message
generation within one method rather than spread among all of the
exception classes. |
java.lang.String |
getGrammarFileName()
For debugging and other purposes, might want the grammar name. |
protected java.lang.Object |
getMissingSymbol(IntStream input,
RecognitionException e,
int expectedTokenType,
BitSet follow)
Conjure up a missing token during error recovery. |
int |
getNumberOfSyntaxErrors()
Get number of recognition errors (lexer, parser, tree parser). |
java.util.List |
getRuleInvocationStack()
Return List of the rules in your parser instance
leading up to a call to this method. |
static java.util.List |
getRuleInvocationStack(java.lang.Throwable e,
java.lang.String recognizerClassName)
A more general version of getRuleInvocationStack where you can
pass in, for example, a RecognitionException to get it's rule
stack trace. |
int |
getRuleMemoization(int ruleIndex,
int ruleStartIndex)
Given a rule number and a start token index number, return
MEMO_RULE_UNKNOWN if the rule has not parsed input starting from
start index. |
int |
getRuleMemoizationCacheSize()
return how many rule/input-index pairs there are in total. |
abstract java.lang.String |
getSourceName()
|
java.lang.String |
getTokenErrorDisplay(Token t)
How should a token be displayed in an error message? The default
is to display just the text, but during development you might
want to have a lot of information spit out. |
java.lang.String[] |
getTokenNames()
Used to print out token names like ID during debugging and
error reporting. |
java.lang.Object |
match(IntStream input,
int ttype,
BitSet follow)
Match current input symbol against ttype. |
void |
matchAny(IntStream input)
Match the wildcard: in a symbol |
void |
memoize(IntStream input,
int ruleIndex,
int ruleStartIndex)
Record whether or not this rule parsed the input at this position
successfully. |
boolean |
mismatchIsMissingToken(IntStream input,
BitSet follow)
|
boolean |
mismatchIsUnwantedToken(IntStream input,
int ttype)
|
protected void |
pushFollow(BitSet fset)
Push a rule's follow set using our own hardcoded stack |
void |
recover(IntStream input,
RecognitionException re)
Recover from an error found on the input stream. |
java.lang.Object |
recoverFromMismatchedSet(IntStream input,
RecognitionException e,
BitSet follow)
Not currently used |
protected java.lang.Object |
recoverFromMismatchedToken(IntStream input,
int ttype,
BitSet follow)
Attempt to recover from a single missing or extra token. |
void |
reportError(RecognitionException e)
Report a recognition problem. |
void |
reset()
reset the parser's state; subclasses must rewinds the input stream |
void |
setBacktrackingLevel(int n)
|
java.util.List |
toStrings(java.util.List tokens)
A convenience method for use most often with template rewrites. |
void |
traceIn(java.lang.String ruleName,
int ruleIndex,
java.lang.Object inputSymbol)
|
void |
traceOut(java.lang.String ruleName,
int ruleIndex,
java.lang.Object inputSymbol)
|
Methods inherited from class java.lang.Object |
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait |
MEMO_RULE_FAILED
public static final int MEMO_RULE_FAILED
- See Also:
- Constant Field Values
MEMO_RULE_UNKNOWN
public static final int MEMO_RULE_UNKNOWN
- See Also:
- Constant Field Values
INITIAL_FOLLOW_STACK_SIZE
public static final int INITIAL_FOLLOW_STACK_SIZE
- See Also:
- Constant Field Values
DEFAULT_TOKEN_CHANNEL
public static final int DEFAULT_TOKEN_CHANNEL
- See Also:
- Constant Field Values
HIDDEN
public static final int HIDDEN
- See Also:
- Constant Field Values
NEXT_TOKEN_RULE_NAME
public static final java.lang.String NEXT_TOKEN_RULE_NAME
- See Also:
- Constant Field Values
state
protected RecognizerSharedState state
- State of a lexer, parser, or tree parser are collected into a state
object so the state can be shared. This sharing is needed to
have one grammar import others and share same error variables
and other state variables. It's a kind of explicit multiple
inheritance via delegation of methods and shared state.
BaseRecognizer
public BaseRecognizer()
BaseRecognizer
public BaseRecognizer(RecognizerSharedState state)
reset
public void reset()
- reset the parser's state; subclasses must rewinds the input stream
match
public java.lang.Object match(IntStream input,
int ttype,
BitSet follow)
throws RecognitionException
- Match current input symbol against ttype. Attempt
single token insertion or deletion error recovery. If
that fails, throw MismatchedTokenException.
To turn off single token insertion or deletion error
recovery, override recoverFromMismatchedToken() and have it
throw an exception. See TreeParser.recoverFromMismatchedToken().
This way any error in a rule will cause an exception and
immediate exit from rule. Rule would recover by resynchronizing
to the set of symbols that can follow rule ref.
- Throws:
RecognitionException
matchAny
public void matchAny(IntStream input)
- Match the wildcard: in a symbol
mismatchIsUnwantedToken
public boolean mismatchIsUnwantedToken(IntStream input,
int ttype)
mismatchIsMissingToken
public boolean mismatchIsMissingToken(IntStream input,
BitSet follow)
reportError
public void reportError(RecognitionException e)
- Report a recognition problem.
This method sets errorRecovery to indicate the parser is recovering
not parsing. Once in recovery mode, no errors are generated.
To get out of recovery mode, the parser must successfully match
a token (after a resync). So it will go:
1. error occurs
2. enter recovery mode, report error
3. consume until token found in resynch set
4. try to resume parsing
5. next match() will reset errorRecovery mode
If you override, make sure to update syntaxErrors if you care about that.
displayRecognitionError
public void displayRecognitionError(java.lang.String[] tokenNames,
RecognitionException e)
getErrorMessage
public java.lang.String getErrorMessage(RecognitionException e,
java.lang.String[] tokenNames)
- What error message should be generated for the various
exception types?
Not very object-oriented code, but I like having all error message
generation within one method rather than spread among all of the
exception classes. This also makes it much easier for the exception
handling because the exception classes do not have to have pointers back
to this object to access utility routines and so on. Also, changing
the message for an exception type would be difficult because you
would have to subclassing exception, but then somehow get ANTLR
to make those kinds of exception objects instead of the default.
This looks weird, but trust me--it makes the most sense in terms
of flexibility.
For grammar debugging, you will want to override this to add
more information such as the stack frame with
getRuleInvocationStack(e, this.getClass().getName()) and,
for no viable alts, the decision description and state etc...
Override this to change the message generated for one or more
exception types.
getNumberOfSyntaxErrors
public int getNumberOfSyntaxErrors()
- Get number of recognition errors (lexer, parser, tree parser). Each
recognizer tracks its own number. So parser and lexer each have
separate count. Does not count the spurious errors found between
an error and next valid token match
See also reportError()
getErrorHeader
public java.lang.String getErrorHeader(RecognitionException e)
- What is the error header, normally line/character position information?
getTokenErrorDisplay
public java.lang.String getTokenErrorDisplay(Token t)
- How should a token be displayed in an error message? The default
is to display just the text, but during development you might
want to have a lot of information spit out. Override in that case
to use t.toString() (which, for CommonToken, dumps everything about
the token). This is better than forcing you to override a method in
your token objects because you don't have to go modify your lexer
so that it creates a new Java type.
emitErrorMessage
public void emitErrorMessage(java.lang.String msg)
- Override this method to change where error messages go
recover
public void recover(IntStream input,
RecognitionException re)
- Recover from an error found on the input stream. This is
for NoViableAlt and mismatched symbol exceptions. If you enable
single token insertion and deletion, this will usually not
handle mismatched symbol exceptions but there could be a mismatched
token that the match() routine could not recover from.
beginResync
public void beginResync()
- A hook to listen in on the token consumption during error recovery.
The DebugParser subclasses this to fire events to the listenter.
endResync
public void endResync()
computeErrorRecoverySet
protected BitSet computeErrorRecoverySet()
computeContextSensitiveRuleFOLLOW
protected BitSet computeContextSensitiveRuleFOLLOW()
- 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 (lookahead 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.
combineFollows
protected BitSet combineFollows(boolean exact)
recoverFromMismatchedToken
protected java.lang.Object recoverFromMismatchedToken(IntStream input,
int ttype,
BitSet follow)
throws RecognitionException
- Attempt to recover from a single missing or extra token.
EXTRA TOKEN
LA(1) is not what we are looking for. If LA(2) has the right token,
however, then assume LA(1) is some extra spurious token. Delete it
and LA(2) as if we were doing a normal match(), which advances the
input.
MISSING TOKEN
If current token is consistent with what could come after
ttype then it is ok to "insert" the missing token, else throw
exception For example, Input "i=(3;" is clearly missing the
')'. When the parser returns from the nested call to expr, it
will have call chain:
stat -> expr -> atom
and it will be trying to match the ')' at this point in the
derivation:
=> ID '=' '(' INT ')' ('+' atom)* ';'
^
match() will see that ';' doesn't match ')' and report a
mismatched token error. To recover, it sees that LA(1)==';'
is in the set of tokens that can follow the ')' token
reference in rule atom. It can assume that you forgot the ')'.
- Throws:
RecognitionException
recoverFromMismatchedSet
public java.lang.Object recoverFromMismatchedSet(IntStream input,
RecognitionException e,
BitSet follow)
throws RecognitionException
- Not currently used
- Throws:
RecognitionException
getCurrentInputSymbol
protected java.lang.Object getCurrentInputSymbol(IntStream input)
- 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.
getMissingSymbol
protected java.lang.Object getMissingSymbol(IntStream input,
RecognitionException e,
int expectedTokenType,
BitSet follow)
- 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.
consumeUntil
public void consumeUntil(IntStream input,
int tokenType)
consumeUntil
public void consumeUntil(IntStream input,
BitSet set)
- Consume tokens until one matches the given token set
pushFollow
protected void pushFollow(BitSet fset)
- Push a rule's follow set using our own hardcoded stack
getRuleInvocationStack
public java.util.List getRuleInvocationStack()
- Return List of the rules in your parser instance
leading up to a call to this method. You could override if
you want more details such as the file/line info of where
in the parser java code a rule is invoked.
This is very useful for error messages and for context-sensitive
error recovery.
getRuleInvocationStack
public static java.util.List getRuleInvocationStack(java.lang.Throwable e,
java.lang.String recognizerClassName)
- A more general version of getRuleInvocationStack where you can
pass in, for example, a RecognitionException to get it's rule
stack trace. This routine is shared with all recognizers, hence,
static.
TODO: move to a utility class or something; weird having lexer call this
getBacktrackingLevel
public int getBacktrackingLevel()
setBacktrackingLevel
public void setBacktrackingLevel(int n)
failed
public boolean failed()
- Return whether or not a backtracking attempt failed.
getTokenNames
public java.lang.String[] getTokenNames()
- Used to print out token names like ID during debugging and
error reporting. The generated parsers implement a method
that overrides this to point to their String[] tokenNames.
getGrammarFileName
public java.lang.String getGrammarFileName()
- For debugging and other purposes, might want the grammar name.
Have ANTLR generate an implementation for this method.
getSourceName
public abstract java.lang.String getSourceName()
toStrings
public java.util.List toStrings(java.util.List tokens)
- A convenience method for use most often with template rewrites.
Convert a List to List
getRuleMemoization
public int getRuleMemoization(int ruleIndex,
int ruleStartIndex)
- Given a rule number and a start token index number, return
MEMO_RULE_UNKNOWN if the rule has not parsed input starting from
start index. If this rule has parsed input starting from the
start index before, then return where the rule stopped parsing.
It returns the index of the last token matched by the rule.
For now we use a hashtable and just the slow Object-based one.
Later, we can make a special one for ints and also one that
tosses out data after we commit past input position i.
alreadyParsedRule
public boolean alreadyParsedRule(IntStream input,
int ruleIndex)
- Has this rule already parsed input at the current index in the
input stream? Return the stop token index or MEMO_RULE_UNKNOWN.
If we attempted but failed to parse properly before, return
MEMO_RULE_FAILED.
This method has a side-effect: if we have seen this input for
this rule and successfully parsed before, then seek ahead to
1 past the stop token matched for this rule last time.
memoize
public void memoize(IntStream input,
int ruleIndex,
int ruleStartIndex)
- Record whether or not this rule parsed the input at this position
successfully. Use a standard java hashtable for now.
getRuleMemoizationCacheSize
public int getRuleMemoizationCacheSize()
- return how many rule/input-index pairs there are in total.
TODO: this includes synpreds. :(
traceIn
public void traceIn(java.lang.String ruleName,
int ruleIndex,
java.lang.Object inputSymbol)
traceOut
public void traceOut(java.lang.String ruleName,
int ruleIndex,
java.lang.Object inputSymbol)
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