bison

I'm having trouble following the steps to make my bison/flex parser reentrant with a minimum amount of fuss. The problem appears to be in the lexer. Since everything parser is re-entrant, I can no longer assign yylval directly. Instead, according to the Flex manual , I have to call this function: void yyset_lval ( YYSTYPE * yylvalp , yyscan_t scanner ); But the problem is, YYSTYPE is an integral type. It isn't a dynamically allocated value, and it isn't an lvalue at all, so I can't pass a pointer to it! Am I missing something, and if not, how am I supposed to set yylvalue? I've never had this

I'm learning flex/bison. I wrote the following program but getting errors. %{ #include <stdio.h> typedef struct node { struct node *left; struct node *right; char *token; }node; node *mknode( node *left, node *right, char *token); void printtree(node *tree); #define YYSTYPE struct node * %} %union { char* str; int num; } %start lines %token <str> WORD %token <str> PLUS MINUS TIMES DIVIDE POWER %token <str> LEFT_PARENTHESIS RIGHT_PARENTHESIS %token <str> END %left PLUS MINUS %left TIMES DIVIDE %right POWER %type <str> exp term factor line lines %% lines: /* empty */ | lines line; line: exp END

In my language i can write a = 1 b = 2 if true { } else { } if true { } **Here is the problem** else {} My grammer doesnt support newlines between statements. An else can only be used with an if. When i add optionalNL in my rule IfExpr: IF rval optionalNL codeBlock optionalNL ELSE codeBlock | IF rval optionalNL codeBlock The optionalNL before the else causes 3 reduce/reduce. Reason is it can reduce using the 2nd rule in IfExpr or reduce to exprLoop where it allows many newlines between expressions. No matter what i do (i tried writing %prec before optionalNL and ELSE) it always reduces to

When dealing with strings (it has its own state like comments) i need to find out if the next letter is a " or not. If it is i dont end the string state. So what happens is i just dont end the string in my string state (i use <STRING_STATE>. and process it letter by letter). So what happens is, i mark if the last string was " and if the current isnt i exit the state and unput the last letter. This has a weird effect. When i get errors on lines with strings i see the letter (usually a ',' or ')') twice. and if it happens to be on the end of the line the side effect counts as two lines! (even if

I have a lexical analyser written in flex that passes tokens to my parser written in bison. The following is a small part of my lexer: ID [a-z][a-z0-9]* %% rule { printf("A rule: %s\n", yytext); return RULE; } {ID} { printf( "An identifier: %s\n", yytext ); return ID; } "(" return LEFT; ")" return RIGHT; There are other bits for parsing whitespace etc too. Then part of the parser looks like this: %{ #include <stdio.h> #include <stdlib.h> #define YYSTYPE char* %} %token ID RULE %token LEFT RIGHT %% rule_decl : RULE LEFT ID RIGHT { printf("Parsing a rule, its identifier is: %s\n", $2); } ; %% It

I've been trying to find examples everywhere but it's been in vain. I am trying to write a basic Ruby interpreter. For this, I wrote a flex lexical file, containing token recognition sentences, and a grammar file. I wish for my grammar to contain semantic type checking. My grammar file contains, for example: arg : arg '+' arg This should be a valid rule for integers and floats. According to what I've read, I can specify type for a non terminal such as arg, like so: %type <intval> arg where "intval" is in the type union and corresponds to the int C type. But this is only for integers, I am not