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|
An overridden Lexer that raises exceptions.
Inherits From: QueryLexer, expected_type
google.appengine.api.search.query_parser.QueryLexerWithErrors(
input=None, state=None
)
Attributes | |
|---|---|
text
|
Return the text matched so far for the current token or any text override. |
Child Classes
class DFA10
class DFA7
class DFA9
Methods
ExclamationNotFollowedByEquals
ExclamationNotFollowedByEquals()
alreadyParsedRule
alreadyParsedRule(
input, 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.
beginResync
beginResync()
A hook to listen in on the token consumption during error recovery. The DebugParser subclasses this to fire events to the listenter.
combineFollows
combineFollows(
exact
)
computeContextSensitiveRuleFOLLOW
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.
computeErrorRecoverySet
computeErrorRecoverySet()
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 ')' 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.
consumeUntil
consumeUntil(
input, tokenTypes
)
Consume tokens until one matches the given token or token set
tokenTypes can be a single token type or a set of token types
displayRecognitionError
displayRecognitionError(
tokenNames, e
)
emit
emit(
token=None
)
The standard method called to automatically emit a token at the outermost lexical rule. The token object should point into the char buffer start..stop. If there is a text override in 'text', use that to set the token's text. Override this method to emit custom Token objects.
If you are building trees, then you should also override Parser or TreeParser.getMissingSymbol().
emitErrorMessage
emitErrorMessage(
msg
)
Raise an exception if the input fails to parse correctly.
Overriding the default, which normally just prints a message to stderr.
| Arguments | |
|---|---|
msg
|
the error message |
| Raises | |
|---|---|
QueryException
|
always. |
endResync
endResync()
A hook to listen in on the token consumption during error recovery. The DebugParser subclasses this to fire events to the listenter.
getBacktrackingLevel
getBacktrackingLevel()
getCharErrorDisplay
getCharErrorDisplay(
c
)
getCharIndex
getCharIndex()
What is the index of the current character of lookahead?
getCharPositionInLine
getCharPositionInLine()
getCurrentInputSymbol
getCurrentInputSymbol(
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.
getErrorHeader
getErrorHeader(
e
)
What is the error header, normally line/character position information?
getErrorMessage
getErrorMessage(
e, 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.
getGrammarFileName
getGrammarFileName()
For debugging and other purposes, might want the grammar name.
Have ANTLR generate an implementation for this method.
getLine
getLine()
getMissingSymbol
getMissingSymbol(
input, e, expectedTokenType, 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.
getNumberOfSyntaxErrors
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()
getRuleInvocationStack
getRuleInvocationStack()
Return List
This is very useful for error messages and for context-sensitive error recovery.
You must be careful, if you subclass a generated recognizers. The default implementation will only search the module of self for rules, but the subclass will not contain any rules. You probably want to override this method to look like
def getRuleInvocationStack(self):
return self.getRuleInvocationStack(
where
getRuleMemoization
getRuleMemoization(
ruleIndex, 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.
getSourceName
getSourceName()
getText
getText()
Return the text matched so far for the current token or any text override.
getTokenErrorDisplay
getTokenErrorDisplay(
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.
mAND
mAND()
mBACKSLASH
mBACKSLASH()
mCOMMA
mCOMMA()
mDIGIT
mDIGIT()
mEQ
mEQ()
mESC
mESC()
mESCAPED_CHAR
mESCAPED_CHAR()
mEXCLAMATION
mEXCLAMATION()
mFIX
mFIX()
mGE
mGE()
mGT
mGT()
mHAS
mHAS()
mHEX_DIGIT
mHEX_DIGIT()
mLE
mLE()
mLESSTHAN
mLESSTHAN()
mLPAREN
mLPAREN()
mMID_CHAR
mMID_CHAR()
mMINUS
mMINUS()
mNE
mNE()
mNOT
mNOT()
mNUMBER_PREFIX
mNUMBER_PREFIX()
mOCTAL_ESC
mOCTAL_ESC()
mOR
mOR()
mQUOTE
mQUOTE()
mREWRITE
mREWRITE()
mRPAREN
mRPAREN()
mSTART_CHAR
mSTART_CHAR()
mTEXT
mTEXT()
mTEXT_ESC
mTEXT_ESC()
mTokens
mTokens()
This is the lexer entry point that sets instance var 'token'
mUNICODE_ESC
mUNICODE_ESC()
mWS
mWS()
match
match(
s
)
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 mismatchRecover() and have it call plain mismatch(), which does not recover. Then 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.
matchAny
matchAny()
Match the wildcard: in a symbol
matchRange
matchRange(
a, b
)
memoize
memoize(
input, ruleIndex, ruleStartIndex, success
)
Record whether or not this rule parsed the input at this position successfully.
mismatch
mismatch(
input, ttype, follow
)
Factor out what to do upon token mismatch so tree parsers can behave differently. Override and call mismatchRecover(input, ttype, follow) to get single token insertion and deletion. Use this to turn of single token insertion and deletion. Override mismatchRecover to call this instead.
mismatchIsMissingToken
mismatchIsMissingToken(
input, follow
)
mismatchIsUnwantedToken
mismatchIsUnwantedToken(
input, ttype
)
next
next()
Return next token or raise StopIteration.
Note that this will raise StopIteration when hitting the EOF token, so EOF will not be part of the iteration.
nextToken
nextToken()
Return a token from this source; i.e., match a token on the char stream.
recover
recover(
re
)
Lexers can normally match any char in its vocabulary after matching a token, so do the easy thing and just kill a character and hope it all works out. You can instead use the rule invocation stack to do sophisticated error recovery if you are in a fragment rule.
recoverFromMismatchedSet
recoverFromMismatchedSet(
input, e, follow
)
Not currently used
recoverFromMismatchedToken
recoverFromMismatchedToken(
input, ttype, follow
)
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 ')'.
reportError
reportError(
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:
- error occurs
- enter recovery mode, report error
- consume until token found in resynch set
- try to resume parsing
- next match() will reset errorRecovery mode
If you override, make sure to update syntaxErrors if you care about that.
reset
reset()
reset the parser's state; subclasses must rewinds the input stream
setCharStream
setCharStream(
input
)
Set the char stream and reset the lexer
setInput
setInput(
input
)
setText
setText(
text
)
Set the complete text of this token; it wipes any previous changes to the text.
skip
skip()
Instruct the lexer to skip creating a token for current lexer rule and look for another token. nextToken() knows to keep looking when a lexer rule finishes with token set to SKIP_TOKEN. Recall that if token==null at end of any token rule, it creates one for you and emits it.
toStrings
toStrings(
tokens
)
A convenience method for use most often with template rewrites.
Convert a List
traceIn
traceIn(
ruleName, ruleIndex
)
traceOut
traceOut(
ruleName, ruleIndex
)
__iter__
__iter__()
The TokenSource is an iterator.
The iteration will not include the final EOF token, see also the note for the next() method.