Antlr V3

ANTLR v3 Overview (for ANTLR v2 users) Terence Parr University of San Francisco

Topics ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Grammar Syntax header {…} /** doc comment */ kind grammar name ; options {…} tokens {…} scopes… action rules … /** doc comment */ rule[String s, int z] returns [int x, int y] throws E options {…} scopes init {…} :  |  ; exceptions ^(root child1 … childN) Trees Note: No inheritance

Grammar improvements ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Example Grammar grammar SimpleParser; program : variable* method+ ; variable: "int" ID (‘=‘ expr)? ';’ ; method : "method" ID '(' ')' '{' variable* statement+ '}' ; statement : ID ‘=‘ expr ';' | "return" expr ';' ; expr : ID | INT ; ID : ('a'..'z'|'A'..'Z')+ ; INT : '0'..'9'+ ; WS : (' '|''|'')+ {channel=99;} ;

Using the parser CharStream in = new ANTLRFileStream(“inputfile”); SimpleParserLexer lexer = new SimpleParserLexer(in); CommonTokenStream tokens = new CommonTokenStream(lexer); SimpleParser p = new SimpleParser(tokens); p.program(); // invoke start rule

Improved grammar warnings ,[object Object],[object Object],[object Object],[object Object]

Recursion Warnings a : a A | B ; t.g:2:5: Alternative 1 discovers infinite left-recursion to a from a t.g:2:5: Alternative 1: after matching input such as B decision cannot predict what comes next due to recursion overflow to c from b // with -Im 0 (secret internal parameter) a : b | B ; b : c ; c : B b ;

Nondeterminisms ,[object Object],[object Object],[object Object],a : (A B|A B) C ; a : (A+ B|A+ B) C ; t.g:2:5: Decision can match input such as "A B" using multiple alternatives: 1, 2

Runtime Objects of Interest ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Error Recovery ,[object Object],[object Object],[object Object],[object Object],[object Object]

Example Error Recovery int i = 0; method foo( { int j = i; i = 4 } [program, method]: line 2:12 mismatched token: [@14,23:23='{',<14>,2:12]; expecting type ')' [program, method, statement]: line 5:0 mismatched token: [@31,46:46='}',<15>,5:0]; expecting type ';' int i = 0; method foo() ) { int j = i; i = = 4; } [program, method]: line 2:13 mismatched token: [@15,24:24=')',<13>,2:13]; expecting type '{' [program, method, statement, expr]: line 4:6 mismatched token: [@32,47:47='=',<6>,4:6]; expecting set null Note: I put in two errors each so you’ll see it continues properly One token insertion One token deletion

Attributes ,[object Object],[object Object],[object Object],a[String s] returns [float y] : id=ID f=field (ids+=ID)+ {$s, $y, $id, $id.text, $f.z; $ids.size();} ; field returns [int x, int z] : … ;

Label properties ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Rule Scope Attributes ,[object Object],[object Object],method scope { String name; } : "method" ID '(' ')' {$name=$ID.text;} body ; body: '{' stat* '}’ ; … atom init {… $ method .name …} : ID | INT ;

Global Scope Attributes ,[object Object],scope Symbols { List names; } {int level=0;} globals scope Symbols; init { level++; $Symbols.names = new ArrayList(); } : decl* {level--;} ; block scope Symbols; init { level++; $Symbols.names = new ArrayList(); } : '{' decl* stat* '}’ {level--;} ; decl : "int" ID ';' {$Symbols.names.add($ID);} ; *What if we want to keep the symbol tables around after parsing?

Tree Support ,[object Object],[object Object],[object Object],[object Object],[object Object]

Tree Construction ,[object Object],[object Object],[object Object],[object Object],[object Object]

Tree Rewrite Rules ,[object Object],variable : type declarator ';' -> ^(VAR_DEF type declarator) ; functionHeader : type ID '(' ( formalParameter ( ',' formalParameter )* )? ')' -> ^(FUNC_HDR type ID formalParameter+) ; atom : … | '(' expr ')' -> expr ;

Mixed Rewrite/Auto Trees ,[object Object],b : ID INT -> INT ID | INT // implies -> INT ;

Rewrites and labels ,[object Object],[object Object],forStat : "for" '(' start=assignStat ';' expr ';' next=assignStat ')' block -> ^("for" $start expr $next block) ; block : lc='{' variable* stat* '}’ -> ^(BLOCK[$lc] variable* stat*) ; /** match string representation of tree and build tree in memory */ tree : ‘^’ ‘(‘ root=atom (children+=tree)+ ‘)’ -> ^($root $children) | atom ;

Loops in Rewrites ,[object Object],[object Object],[object Object],[object Object]

Preventing cyclic structures ,[object Object],[object Object],[object Object],[object Object],*Just noticed a bug in this one ;)

Predicated rewrites ,[object Object],a : ID INT -> {p1}? ID -> {p2}? INT -> ;

Misc Rewrite Elements ,[object Object],[object Object],[object Object],b : "int" ( ID -> ^(TYPE "int" ID) | ID '=' INT -> ^(TYPE "int" ID INT) ) ; a : (atom -> atom) (op='+' r=atom -> ^($op $a $r) )* ;

Tree Grammars ,[object Object],[object Object],variable : ^(VAR_DEF type ID) | ^(VAR_DEF type ID ^(INIT expr)) ;

Code Generation ,[object Object],[object Object],[object Object]

Sample code gen templates /** Dump the elements one per line and stick in debugging * location() trigger in front. */ element() ::= << <if(debug)> dbg.location(<it.line>,<it.pos>);<> <endif> <it.el><> >> /** match a token optionally with a label in front */ tokenRef(token,label,elementIndex) ::= << <if(label)> <label>=input.LT(1);<> <endif> match(input,<token>,FOLLOW_<token>_in_<ruleName><elementIndex>); >>

Internationalization ,[object Object],[object Object],[object Object],RULE_REDEFINITION(file,line,col,arg) ::= "<loc()>rule <arg> redefinition” /* This factors out file location formatting; file,line,col inherited from * enclosing template; don't manually pass stuff in. */ loc() ::= "<file>:<line>:<col>: "

Runtime Support ,[object Object],[object Object],[object Object]

Summary ,[object Object],[object Object],[object Object],[object Object]

Antlr V3

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