antlr - ANother Tool for Language Recognition antlr [options] grammar_files Antlr converts an extended form of context-free grammar into a set of C functions which directly implement an efficient form of deterministic recursive-descent LL(k) parser. Context-free grammars may be augmented with predicates to allow semantics to influence pars- ing; this allows a form of context-sensitive parsing. Antlr also pro- duces a definition of a lexer which can be automatically converted into C code for a DFA-based lexer by dlg. Hence, antlr serves a func- tion much like that of yacc, however, it is notably more flexible and is more integrated with a lexer generator (antlr directly generates dlg code, whereas yacc and lex are given independent descriptions). Unlike yacc which accepts LALR(1) grammars, antlr accepts LL(k) gram- mars in an extended BNF notation - which eliminates the need for pre- cedence rules. Like yacc grammars, antlr grammars can use automatically- maintained symbol attribute values referenced as dollar variables. Further, because antlr generates top-down parsers, arbitrary values may be inherited from parent rules (passed like function parameters). Antlr also has a mechanism for creating and manipulating abstract- syntax-trees. There are various other niceties in antlr, including the ability to spread one grammar over multiple files or even multiple grammars in a single file, the ability to generate a version of the grammar with actions stripped out (for documentation purposes), and lots more. -cr Generate a cross-reference for all rules. For each rule, print a list of all other rules that reference it. -e1 Ambiguities/errors shown in low detail (default). -e2 Ambiguities/errors shown in more detail. -e3 Ambiguities/errors shown in excrutiating detail. -fe file Rename err.c to file. -fh file Rename stdpccts.h header (turns on -gh) to file. -fl file Rename lexical output, parser.dlg, to file. -ft file Rename tokens.h to file. Page 1 PCCTS -ga Generate ANSI-compatible code (default case). This has not been rigorously tested to be ANSI XJ11 C compliant, but it is close. The normal output of antlr is currently compilable under both K&R and ANSI C-this option does nothing, but is reserved for the future. -gc Indicates that antlr should generate no C code, i.e., only per- form analysis on the grammar. -gd C code is inserted in each of the antlr generated parsing func- tions to provide for user-defined handling of a detailed parse trace. The inserted code consists of calls to the user-supplied macros or functions called zzTRACEIN and zzTRACEOUT. The only argument is a char * pointing to a C-style string which is the grammar rule recognized by the current parsing function. If no definition is given for the trace functions, upon rule entry and exit, a message will be printed indicating that a particular rule as been entered or exited. -ge Generate an error class for each non-terminal. -gh Generate stdpccts.h for non-ANTLR-generated files to include. This file contains all defines needed to describe the type of parser generated by antlr (e.g. how much lookahead is used and whether or not trees are constructed) and contains the header action specified by the user. -gk Generate parsers that delay lookahead fetches until needed. Without this option, antlr generates parsers which always have k tokens of lookahead available. This option is incompatible with -pr and renders references to LA(i) invalid as one never knows when the ith token of lookahead will be fetched. -gl Generate line info about grammar actions in C parser of the form # line "file" which makes error messages from the C/C++ compiler make more sense as they will "point" into the grammar file not the resulting C file. Debugging is easier as well, because you will step through the grammar not C file. -gp prefix Prefix all functions generated from rules with prefix. -gs Do not generate sets for token expression lists; instead generate a ||-separated sequence of LA(1)==token_number. The default is to generate sets. -gt Generate code for Abstract-Syntax Trees. -gx Do not create the lexical analyzer files (dlg-related). This option should be given when the user wishes to provide a custom- ized lexical analyzer. It may also be used in make scripts to cause only the parser to be rebuilt when a change not affecting the lexical structure is made to the input grammars. Page 2 PCCTS -k n Set k of LL(k) to n; i.e. set tokens of look-ahead (default==1). -p The complete grammar, collected from all input grammar files and stripped of all comments and embedded actions, is listed to stdout. This is intended to aid in viewing the entire grammar as a whole and to eliminate the need to keep actions concisely stated so that the grammar is easier to read. Hence, it is preferable to embed even complex actions directly in the grammar, rather than to call them as subroutines, since the subroutine call overhead will be saved. -pa This option is the same as -p except that the output is annotated with the first sets determined from grammar analysis. -pr Turn on use of predicates in parsing decisions (alpha version). When a syntactic ambiguity is discovered, antlr searches for predicates that can be used to disambiguate the decision. Predi- cates have dual roles as semantic validation and disambiguation predicates. -rl Limit the maximum number of tree nodes used by grammar analysis to n. Occasionally, antlr is unable to analyze a grammar submit- ted by the user. This rare situation can only occur when the grammar is large and the amount of lookahead is greater than one. A nonlinear analysis algorithm is used by PCCTS to handle the general case of LL(k) parsing. The average complexity of analysis, however, is near linear due to some fancy footwork in the implementation which reduces the number of calls to the full LL(k) algorithm. An error message will be displayed, if this limit is reached, which indicates the grammar construct being analyzed when antlr hit a non-linearity. Use this option if antlr seems to go out to lunch and your disk start thrashing; try n=10000 to start. Once the offending construct has been identi- fied, try to remove the ambiguity that antlr was trying to over- come with large lookahead analysis. Antlr works... we think. There is no implicit guarantee of any- thing. We reserve no legal rights to the software known as the Purdue Compiler Construction Tool Set (PCCTS) - PCCTS is in the public domain. An individual or company may do whatever they wish with source code distributed with PCCTS or the code generated by PCCTS, including the incorporation of PCCTS, or its output, into commerical software. We encourage users to develop software with PCCTS. How- ever, we do ask that credit is given to us for developing PCCTS. By "credit", we mean that if you incorporate our source code into one of your programs (commercial product, research project, or otherwise) that you acknowledge this fact somewhere in the documentation, research report, etc... If you like PCCTS and have developed a nice tool with the output, please mention that you developed it using PCCTS. As long as these guidelines are followed, we expect to con- tinue enhancing this system and expect to make other tools available as they are completed. Page 3 PCCTS *.c output C parser parser.dlg output dlg lexical analyzer err.ctoken string array, error sets and error support routines tokens.h output #defines for tokens used and function prototypes for func- tions generated for rules stdpccts.h list of definitions needed by C files, not generated by PCCTS, that reference PCCTS objects. This is not generated by default. dlg(1), pccts(1) Page 4