Flex & bison by John R Levine; Safari Tech Books Online

By John R Levine; Safari Tech Books Online

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The definition of calclist uses a common two-rule recursive idiom to implement a sequence or list: the first rule is empty and matches nothing; the second adds an item to the list. The action in the second rule prints the value of the exp in $2. The rest of the rules implement the calculator. The rules with operators such as exp ADD factor and ABS term do the appropriate arithmetic on the symbol values. The rules with a single symbol on the right side are syntactic glue to put the grammar together; for example, an exp is a factor.

Each reference has a flags value that isn’t used here but will be when we reuse this code in the next example. b->name) return -1; return strcmp(a->name, b->name); void printrefs() { struct symbol *sp; qsort(symtab, NHASH, sizeof(struct symbol), symcompare); /* sort the symbol table */ for(sp = symtab; sp->name && sp < symtab+NHASH; sp++) { char *prevfn = NULL; /* last printed filename, to skip dups */ /* reverse struct ref struct ref struct ref the list of references */ *rp = sp->reflist; *rpp = 0; /* previous ref */ *rpn; /* next ref */ do { rpn = rp->next; rp->next = rpp; rpp = rp; rp = rpn; } while(rp); } } /* now print the word and its references */ printf("%10s", sp->name); for(rp = rpp; rp; rp = rp->next) { if(rp->filename == prevfn) { printf(" %d", rp->lineno); } else { printf(" %s:%d", rp->filename, rp->lineno); prevfn = rp->filename; } } printf("\n"); The final routines sort and print the symbol table.

It switches to IFILE state to read the next input filename. In IFILE state, the second pattern matches a filename, characters up to a closing quote, whitespace, or end-of-line. The filename is passed to newfile to stack the current input file and set up the next level of input, but first there’s the matter of dealing with whatever remains of the #include line. One possibility would be to use another start state and patterns that absorb the rest of the line, but that would be tricky, since the action switches to the included file, so the start state and pattern would have to be used after the end of the included file.

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