{"id":46,"date":"2008-10-14T18:48:21","date_gmt":"2008-10-14T16:48:21","guid":{"rendered":"http:\/\/floris.briolas.nl\/floris\/?p=46"},"modified":"2014-10-17T15:10:17","modified_gmt":"2014-10-17T13:10:17","slug":"antlr-common-pittfals","status":"publish","type":"post","link":"https:\/\/floris.briolas.nl\/floris\/2008\/10\/antlr-common-pittfals\/","title":{"rendered":"ANTLR common pitfalls"},"content":{"rendered":"

Personally I think ANTLR is a great tool, It has a steep learning curve and it has a few quirks. I hope the description here will help you find your problem, understand it and help you fix the issue.<\/p>\n

Recognition problems<\/strong><\/p>\n

Recognizes number as ‘1234’ but not as ‘1’:
\nExample:<\/p>\n

\r\ngrammar number;\r\n\r\nnumber :\tINT;\r\nDIGIT\t:\t'0'..'9';\r\nINT\t:\tDIGIT+;\r\n<\/pre>\n
Explanation, the input such as ‘1’ or ‘4’ is just one char, it will be recognized as a ‘DIGIT’, not as an ‘INT’. You have two options :
\n– delete the DIGIT rule, and rewrite the INT rule as ” INT:’0′..’9′; ” (works)
\n– place the ‘fragment’ keyword in front of DIGIT. DIGIT will not be seen as a token.<\/p>\n
Grammar Check Errors<\/strong><\/p>\n
The following token definitions are unreachable: INT (AntlrWorks 1.1.7)
\nThe following token definitions can never be matched because prior tokens match the same input: INT (AntlrWorks 1.2) (AntlrWorks 1.3) <\/p>\n
Example:<\/p>\n
\r\ngrammar number;\r\n\r\nDIGIT:\t'0'..'9';\r\nINT\t:\tDIGIT;\r\n<\/pre>\n
What has INT to offer? As is it is a redundant rule. Probably you meant more than one number (thus matching 43) so make it INT : DIGIT+;<\/p>\n
Another possibility:<\/strong><\/p>\n
\r\nfactExpression:\tFact fact;\r\nfact \t:\tID;\r\n\r\npropertyExpression:\tfact Property property;\r\n\r\nproperty:\tID;\r\n\r\nNEWLINE\t:\t'\\r'?'\\n';\r\nWS\t:\t(' ' | '\\t' | '\\n' | '\\r') { skip(); };\r\n\r\nFact\t: 'There is ' ARTICLE \/\/added extra space since it needs to be there\r\n;\r\n\r\nProperty\r\n:\t'has '  ARTICLE \/\/added extra space since it needs to be there\r\n;\r\n\r\nID \t:\t('a'..'z'|'A'..'Z')+;\r\n\r\nARTICLE\r\n:\t('a'|'an')\r\n;\r\n<\/pre>\n
Here the error is “The following token…match the same input: ARTICLE”. ID can both match ‘a’ and ‘an’, but in this case ARTICLE is more important. Flip the ID and ARTICLE rule, and it’s fine.
\nMore on Ambiguous rules.<\/a><\/strong><\/span><\/p>\n
\n
syntax error: codegen: :0:0: unexpected end of subtree (AntlrWorks 1.1.7 & 1.2)
\nExample:<\/p>\n
\r\ngrammar number;\r\n\/\/number \t:\tINT | FLOAT;\r\nDIGIT\t :\t'0'..'9';\r\nINT\t:\tDIGIT+;\r\nFLOAT\t:\tDIGIT* '.' DIGIT+;\r\n<\/pre>\n
You are working with a mixed grammar (both LEXER and PARSER).
\nYou did not include any parser rules, please do so. Uncomment the ‘number’ parser rule.
\nAnother possibility:<\/strong> is that the last line of your grammar is comment, just move it.<\/p>\n
*Updated 10-nov-2009 : Added internal link to explain more on Ambiguous rules.;
\n*Updated 13-oct-2009 : Syntax Highlighting;
\n*Updated 25-jan-2010 : Small updates
\n*Updated 17-ock-2014 : Ending support for antlr 3. Thank you, it was fun!<\/p>\n","protected":false},"excerpt":{"rendered":"
Personally I think ANTLR is a great tool, It has a steep learning curve and it has a few quirks. I hope the description here will help you find your problem, understand it and help you fix the issue. Recognition problems Recognizes number as ‘1234’ but not as ‘1’: Example: grammar number; number : INT; […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"jetpack_post_was_ever_published":false,"_jetpack_newsletter_access":"","_jetpack_newsletter_tier_id":0,"jetpack_publicize_message":"","jetpack_is_tweetstorm":false,"jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":false,"jetpack_social_options":{"image_generator_settings":{"template":"highway","enabled":false}}},"categories":[3],"tags":[6],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/p61yPs-K","_links":{"self":[{"href":"https:\/\/floris.briolas.nl\/floris\/wp-json\/wp\/v2\/posts\/46"}],"collection":[{"href":"https:\/\/floris.briolas.nl\/floris\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/floris.briolas.nl\/floris\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/floris.briolas.nl\/floris\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/floris.briolas.nl\/floris\/wp-json\/wp\/v2\/comments?post=46"}],"version-history":[{"count":19,"href":"https:\/\/floris.briolas.nl\/floris\/wp-json\/wp\/v2\/posts\/46\/revisions"}],"predecessor-version":[{"id":141,"href":"https:\/\/floris.briolas.nl\/floris\/wp-json\/wp\/v2\/posts\/46\/revisions\/141"}],"wp:attachment":[{"href":"https:\/\/floris.briolas.nl\/floris\/wp-json\/wp\/v2\/media?parent=46"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/floris.briolas.nl\/floris\/wp-json\/wp\/v2\/categories?post=46"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/floris.briolas.nl\/floris\/wp-json\/wp\/v2\/tags?post=46"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}