flex-lexer

I have a problem with compilation of my code: Flex: %{ #include "lista4.tab.hpp" #include <stdlib.h> extern int yylex(); %} %% "=" {return EQ;} "!=" {return NE;} "<" {return LT;} ">" {return GT;} ":=" {return ASSIGN;} ";" {return SEMICOLON;} "IF" {return IF;} "THEN"{return THEN;} "END" {return END;} [_a-z]+ {yylval.text = strdup(yytext); return IDENTIFIER;} [ \t]+ [0-9]+ { yylval.var = atoi (yytext); return NUMBER; } [-+/^*'%'()] { return *yytext; } \n return RESULT; %% Bison: %{ extern "C" { int yyparse(); int yylex(void); void yyerror(char *s){} int yywrap(void){return 1;} } #include

I am studying compilers and am learning about lexical analysis. I understand that one specifies each lexeme as a regular expression, and using flex , a lexer can be automatically generated. I am further learning about how the regular expression is converted to an NFA which is then converted to a DFA, where it can be quickly evaluated. However, my question is, how is the maximal-munch rule implemented? Internally, how does the lexer know to "keep going" to find the longest possible lexeme? Thanks! The maximal munch algorithm is implemented by adding a small amount of mutable state to the DFA

I am trying to translate my .spl file into a C file (because there is no compiler). I have an example "Hello World" .spl file, and I have downloaded the Shakespeare Programming Language .tar and extracted it, but I have no idea what to do next. I can't seem to find instructions in any documentation. Can anyone help? Edit: When I type make -f "Makefile" , I get the following output: bison --verbose -d grammar.y gcc -O2 -Wall -c grammar.tab.c gcc -O2 -Wall -c makescanner.c gcc makescanner.o -O2 -Wall -o makescanner ./makescanner include > scanner.l flex -Cem -t scanner.l > scanner.c scanner.l

I'm trying to parse a legacy language (which is similar to 'C') using FLEX and BISON. Everything is working nicely except for matching strings. This rather odd legacy language doesn't support quoting characters in string literals, so the following are all valid string literals: "hello" "" "\" I'm using the following rule to match string literals: \".*\" { yylval.strval = _strdup( yytext ); return LIT_STRING; } Unfortunately this is a greedy match, so it matches code like the following: "hello", "world" As a single string ( hello", "world ). The usual non-greedy quantifier .*? doesn't seem to

I'm trying to parse C-style multi-line comments in my flex (.l) file: %s ML_COMMENT %% ... <INITIAL>"/*" BEGIN(ML_COMMENT); <ML_COMMENT>"*/" BEGIN(INITIAL); <ML_COMMENT>[.\n]+ { } I'm not returning any token and my grammar (.y) doesn't address comments in any way. When I run my executable, I get a parse error: $ ./a.out /* abc def Parse error: parse error $ echo "/* foo */" | ./a.out Parse error: parse error (My yyerror function does a printf("Parse error: %s\n"), which is where the first half of the redundant error message comes from). I can see why the second example fails since the entirety

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