Suppose need the grammar to parse the following templates:
1. REPORT
2. BEGIN
3. QUERY
4. BEGIN
5. AGGREGATION: day
6. DIMENSION: department
7. END
8. END
Where line #5 and #6 are optional and the order of the 2 lines doesn't matter. How can I specify this in my grammar file? Below is my solution (see line #12):
1. grammar PRL;
2. report
3. : REPORT
4. BEGIN
5. query
6. END
7. ;
8.
9. query
10. : QUERY
11. BEGIN
12. (aggregation_decl dimension_decl | dimension_decl aggregation_decl)?
13. END
14. ;
So it works, however it looks ugly, and if I have more than 2 parts it's going to become unmanageable very quickly? Any advice?
Something like this? Generally you would enforce only one of each item exists at a later processing step. Otherwise, as you see, the grammar gets unwieldy.
grammar PRL;
report
: REPORT
BEGIN
query
END
;
query
: QUERY
BEGIN
body_decl*
END
;
body_decl :
aggregation_decl dimension_decl
| dimension_decl aggregation_decl;
As already mentioned by Adam: this generally something done after the parser has created some sort of (abstract) parse tree. You simply collect all types of declarations like this:
grammar PRL;
report
: REPORT BEGIN query END
;
query
: QUERY BEGIN decl* END
;
decl
: NAME ':' NAME
;
REPORT : 'REPORT';
BEGIN : 'BEGIN';
END : 'END';
QUERY : 'QUERY';
NAME : ('a'..'z' | 'A'..'Z')+;
SPACE : (' ' | '\t' | '\r' | '\n')+ {skip();};
and after that, check if there are duplicates in decl* in your AST.
But if you really want to do this during parsing, you need to grab the left hand side of decl and add these in a Set and when you stumble upon a duplicate, throw a predicate exception:
grammar PRL;
#parser::header {
import java.util.Set;
import java.util.HashSet;
}
report
: REPORT BEGIN query END
;
query
: QUERY BEGIN unique_decls END
;
unique_decls
#init{Set<String> set = new HashSet<String>();}
: (decl {set.add($decl.key)}?)*
;
decl returns[String key]
: k=NAME ':' NAME {$key = $k.text;}
;
REPORT : 'REPORT';
BEGIN : 'BEGIN';
END : 'END';
QUERY : 'QUERY';
NAME : ('a'..'z' | 'A'..'Z')+;
SPACE : (' ' | '\t' | '\r' | '\n')+ {skip();};
The {set.add($decl.key)}?, called a Validating Semantic Predicates, will throw an exception when the code inside it (set.add($decl.key)) evaluates to false. In this case, it evaluates to false whenever the set already contains a certain key.
Related
I am trying to update an ANTLR grammar that follows the following spec
https://github.com/facebook/graphql/pull/327/files
In logical terms its defined as
StringValue ::
- `"` StringCharacter* `"`
- `"""` MultiLineStringCharacter* `"""`
StringCharacter ::
- SourceCharacter but not `"` or \ or LineTerminator
- \u EscapedUnicode
- \ EscapedCharacter
MultiLineStringCharacter ::
- SourceCharacter but not `"""` or `\"""`
- `\"""`
(Not the above is logical - not ANTLR syntax)
I tried the follow in ANTRL 4 but it wont recognize more than 1 character inside a triple quoted string
string : triplequotedstring | StringValue ;
triplequotedstring: '"""' triplequotedstringpart? '"""';
triplequotedstringpart : EscapedTripleQuote* | SourceCharacter*;
EscapedTripleQuote : '\\"""';
SourceCharacter :[\u0009\u000A\u000D\u0020-\uFFFF];
StringValue: '"' (~(["\\\n\r\u2028\u2029])|EscapedChar)* '"';
With these rules it will recognize '"""a"""' but as soon as I add more characters it fails
eg: '"""abc"""' wont parse and the IntelliJ plugin for ANTLR says
line 1:14 extraneous input 'abc' expecting {'"""', '\\"""', SourceCharacter}
How do I do triple quoted strings in ANTLR with '\"""' escaping?
Some of your parer rules should really be lexer rules. And SourceCharacter should probably be a fragment.
Also, instead of EscapedTripleQuote* | SourceCharacter*, you probably want ( EscapedTripleQuote | SourceCharacter )*. The first matches aaa... or bbb..., while you probably meant to match aababbba...
Try something like this instead:
string
: Triplequotedstring
| StringValue
;
Triplequotedstring
: '"""' TriplequotedstringPart*? '"""'
;
StringValue
: '"' ( ~["\\\n\r\u2028\u2029] | EscapedChar )* '"'
;
// Fragments never become a token of their own: they are only used inside other lexer rules
fragment TriplequotedstringPart : EscapedTripleQuote | SourceCharacter;
fragment EscapedTripleQuote : '\\"""';
fragment SourceCharacter :[\u0009\u000A\u000D\u0020-\uFFFF];
I apologize in advance if this question has already been asked, can't seem to find it.
I'm just beginning with Antlr, using the antlr4IDE for Eclipse to create a parser for a small subset of Java. For some reason, unless I explicitly state the presence of a white space in my regex, the parser will throw an error.
My grammar:
grammar Hello;
r :
(Statement ';')+
;
Statement:
DECL | INIT
;
DECL:
'int' ID
;
INIT:
DECL '=' NUMEXPR
;
NUMEXPR :
Number OP Number | Number
;
OP :
'+'
| '-'
| '/'
| '*'
;
WS :
[ \t\r\n\u000C]+ -> skip
;
Number:
[0-9]+
;
ID :
[a-zA-Z]+
;
When trying to parse
int hello = 76;
I receive the error:
Hello::r:1:0: mismatched input 'int' expecting Statement
Hello::r:1:10: token recognition error at: '='
However, when I manually add the token WS into the rules, I receive no error.
Any ideas where I'm going wrong? I'm new to Antlr, so I'm probably making a stupid mistake. Thanks in advance.
EDIT : Here is my parse tree and error log:
Error Log:
Change syntax like this.
grammar Hello;
r : (statement ';')+ ;
statement : decl | init ;
decl : 'int' ID ;
init : decl '=' numexpr ;
numexpr : Number op Number | Number ;
op : '+' | '-' | '/' | '*' ;
WS : [ \t\r\n\u000C]+ -> skip ;
Number : [0-9]+ ;
ID : [a-zA-Z]+ ;
After looking at the documentation on antlr4, it seems like you have to have a specification for all of the character combinations that you expect to see in your file, from start to finish - not just those that you want to handle.
In that regards, it's expected that you would have to explicitly state the whitespace, with something like:
WS : [ \t\r\n]+ -> skip;
That's why the skip command exists:
A 'skip' command tells the lexer to get another token and throw out the current text.
Though note that sometimes this can cause a little trouble such as in this post.
I am trying to parse the following:
SELECT name-of-key[random text]
This is part of a larger grammar which I am trying to construct. I left it our for clarity.
I came up with the following rules:
select : 'select' NAME '[' anything ']'
;
anything : (ANYTHING | NAME)+
;
NAME : ('a'..'z' | 'A'..'Z' | '0'..'9' | '-' | '_')+
;
ANYTHING : (~(']' | '['))+
;
WHITESPACE : ('\t' | ' ' | '\r' | '\n')+ -> skip
;
This doesn't seem to work. For example, input SELECT a[hello world!] gives the following error:
line 1:0 mismatched input 'SELECT a' expecting 'SELECT'
This goes wrong because the input SELECT a is recognized by ANYTHING, instead of select. How do I fix that? I feel that I am missing some concept(s) here, but it is difficult to get started.
Maybe the concept you are missing is rule priority.
[1] Lexer rules matching the longest possible string have priority.
As you mentioned, the ANYTHING token rule above matches "select a", which is longer than what the (implicit) token rule 'select' matches, hence its precedence. Non-greedy behaviour is indicated by a question mark.
ANYTHING : (~(']' | '['))+?
Just making the ANYTHING rule non-greedy doesn't completely solve your problem though, because after properly matching 'select', the lexer will produce an ANYTHING token for the space, because ...
[2] Lexer rules appearing first have priority.
Switching lexer rules WHITE_SPACE and ANYTHING fixes this. The grammar below should parse your example.
select : 'select' NAME '[' anything ']'
;
anything : (ANYTHING | NAME)+
;
NAME : ('a'..'z' | 'A'..'Z' | '0'..'9' | '-' | '_')+
;
WHITESPACE : ('\t' | ' ' | '\r' | '\n')+ -> skip
;
ANYTHING : (~(']' | '['))+?
;
I personally avoid implicit token rules, especially if your grammar is complex, precisely because of token rule priority. I would thus write this.
SELECT : 'select' ;
L_BRACKET : '[';
R_BRACKET : ']';
NAME : ('a'..'z' | 'A'..'Z' | '0'..'9' | '-' | '_')+ ;
WHITESPACE : ('\t' | ' ' | '\r' | '\n')+ -> skip ;
ANY : . ;
select : SELECT NAME L_BRACKET anything R_BRACKET ;
anything : (~R_BRACKET)+ ;
Also note that the space in "hello world" will be swallowed by the WHITESPACE rule. To properly manage this, you need ANTLR island grammars.
'Hope this helps!
I am developing my own DSL in XText.
I want do something like this:
1 AND (2 OR (3 OR 4))
Here my current .xtext file:
grammar org.xtext.example.mydsl.MyDsl with org.eclipse.xtext.common.Terminals
generate myDsl "http://www.xtext.org/example/mydsl/MyDsl"
Model:
(greetings+=CONDITION_LEVEL)
;
terminal NUMBER :
('1'..'9') ('0'..'9')*
;
AND:
' AND '
;
OR:
' OR '
;
OPERATOR :
AND | OR
;
CONDITION_LEVEL:
('('* NUMBER (=>')')* OPERATOR)+ NUMBER ')'*
;
The problem I am having is that the dsl should have the possibility to make unlimited bracket, but show an error when the programmer don't closes all opened bracket.
example:
1 AND (2 OR (3 OR 4)
one bracket is missing --> should make error.
I don't know how I can realize this in XText. Can anybody help?
thx for helping.
Try this:
CONDITION_LEVEL
: ATOM ((AND | OR) ATOM)*
;
ATOM
: NUMBER
| '(' CONDITION_LEVEL ')'
;
Note that I have no experience with XText (so I did not test this), but this does work with ANTLR, on which XText is built (or perhaps it only uses ANTLR...).
Aslo, you probably don't want to surround your operator-tokens with spaces, but put them on a hidden-parser channel:
grammar org.xtext.example.mydsl.MyDsl hidden(SPACE)
...
terminal SPACE : (' '|'\t'|'\r'|'\n')+;
...
Otherwise source like this would fail:
1 AND(2 OR 3)
For details, see Hidden Terminal Symbols from the XText user guide.
You need to make your syntax recursive. The basic idea is that a CONDITION_LEVEL can be, for example, two CONDITION_LEVEL separated by an OPERATOR.
I don't know the specifics of the xtext syntax, but using a BCNF-like syntax you could have:
CONDITION_LEVEL:
NUMBER
'(' CONDITION_LEVEL OPERATOR CONDITION_LEVEL ')'
During taking advantage of ANTLR 3.3, I'm changing the current grammar to support inputs without parenthesis too. Here's the first version of my grammar :
grammar PropLogic;
NOT : '!' ;
OR : '+' ;
AND : '.' ;
IMPLIES : '->' ;
SYMBOLS : ('a'..'z') | '~' ;
OP : '(' ;
CP : ')' ;
prog : formula EOF ;
formula : NOT formula
| OP formula( AND formula CP | OR formula CP | IMPLIES formula CP)
| SYMBOLS ;
WHITESPACE : ( '\t' | ' ' | '\r' | '\n'| '\u000C' )+ { $channel = HIDDEN; } ;
Then I changed it this way to support the appropriate features :
grammar PropLogic;
NOT : '!' ;
OR : '+' ;
AND : '.' ;
IMPLIES : '->' ;
SYMBOL : ('a'..'z') | '~' ;
OP : '(' ;
CP : ')' ;
EM : '' ;
prog : formula EOF ;
formula : OP formula( AND formula CP | OR formula CP | IMPLIES formula CP)
| ( NOT formula | SYMBOL )( AND formula | OR formula | IMPLIES formula | EM ) ;
WHITESPACE : ( '\t' | ' ' | '\r' | '\n'| '\u000C' )+ { $channel = HIDDEN; } ;
But I've been faced with following error :
error<100>: syntax error: invalid char literal: ''
error<100>: syntax error: invalid char literal: ''
Does anybody know that how can I overcome this error?
Your EM token:
EM : '' ;
is invalid: you can't match an empty string in lexer rules.
To match epsilon (nothing), you should do:
rule
: A
| B
| /* epsilon */
;
Of course, the comment /* epsilon */ can safely be removed.
Note that when you do it like that in your current grammar, ANTLR will complain that there can be rules matched using multiple alternatives. This is because your grammar is ambiguous.
I'm not an ANTLR expert, but you might try:
formula : term ((AND | OR | IMPLIES ) term )*;
term : OP formula CP | NOT term | SYMBOL ;
If you want traditional precedence of operators this won't do the trick, but that's another issue.
EDIT: OP raised the ante; he wants precedence too. I'll meet him halfway, since it wasn't part
of the orginal question. I've added precedence to the grammar that makes IMPLIES
the lower precedence than other operators, and leave it to OP to figure out how to do the rest.
formula: disjunction ( IMPLIES disjunction )* ;
disjunction: term (( AND | OR ) term )* ;
term: OP formula CP | NOT term | SYMBOL ;
OP additionally asked, "how to convert (!p or q ) into p -> q". I think he should
have asked this as a separate question. However, I'm already here.
What he needs to do is walk the tree, looking for the pattern he doesn't
like, and change the tree into one he does, and then prettyprint the answer.
It is possible to do all this with ANTLR, which is part of the reason
it is popular.
As a practical matter, procedurally walking the tree and checking the node
types, and splicing out old nodes and splicing in new is doable, but a royal PitA.
Especially if you want to do this for lots of transformations.
A more effective way to do this is to use a
program transformation system, which allows surface syntax patterns to be expressed for matching and replacement. Program transformation systems of course include parsing machinery and more powerful ones let you (and indeed insist) that you define
a grammar up front much as you for ANTLR.
Our DMS Software Reengineering Toolkit is such a program transformation tool, and with a suitably defined grammar for propositions,
the following DMS transformation rule would carry out OP's additional request:
domain proplogic; // tell DMS to use OP's definition of logic as a grammar
rule normalize_implies_from_or( p: term, q: term): formula -> formula
" NOT \p OR \q " -> " \p IMPLIES \q ";
The " ... " is "domain notation", e.g, surface syntax from the proplogic domain, the "\" are meta-escapes,
so "\p" and "\q" represent any arbitrary term from the proplogic grammar. Notice the rule has to reach "across" precedence levels when being applied, as "NOT \p OR \q" isn't a formula and "\p IMPLIES \q" is; DMS takes care of all this (the "formula -> formula" notation is how DMS knows what to do). This rule does a tree-to-tree rewrite. The resulting tree can be prettyprinted by DMS.
You can see a complete example of something very similar, e.g., a grammar for conventional algebra and rewrite rule to simplify algebraic equations.