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Reported by Agency for Defense Development. https://lists.gnu.org/r/bug-bison/2020-08/msg00008.html On an empty such as %token FOO BAR FOO 0 %% input: %empty we crash because when we find FOO 0, we decrement ntokens (since FOO was discovered to be EOF, which is already known to be a token, so we increment ntokens for it, and need to cancel this). This "works well" when EOF is properly defined in one go, but here it is first defined and later only assign token code 0. In the meanwhile BAR was given the token number that we just decremented. To fix this, assign symbol numbers after parsing, not during parsing, so that we also saw all the explicit token codes. To maintain the current numbers (I'd like to keep no difference in the output, not just equivalence), we need to make sure the symbols are numbered in the same order: that of appearance in the source file. So we need the locations to be correct, which was almost the case, except for nterms that appeared several times as LHS (i.e., several times as "foo: ..."). Fixing the use of location_of_lhs sufficed (it appears it was intended for this use, but its implementation was unfinished: it was always set to "false" only). * src/symtab.c (symbol_location_as_lhs_set): Update location_of_lhs. (symbol_code_set): Remove broken hack that decremented ntokens. (symbol_class_set, dummy_symbol_get): Don't set number, ntokens and nnterms. (symbol_check_defined): Do it. (symbols): Don't count nsyms here. Actually, don't count nsyms at all: let it be done in... * src/reader.c (check_and_convert_grammar): here. Define nsyms from ntokens and nnterms after parsing. * tests/input.at (EOF redeclared): New. * examples/c/bistromathic/bistromathic.test: Adjust the traces: in "%nterm <double> exp %% input: ...", exp used to be numbered before input.
This directory contains examples of Bison grammar files, sorted per language.
Several of them come from the documentation, which should be installed together with Bison. The URLs are provided for convenience.
These examples come with a README and a Makefile. Not only can they be used to toy with Bison, they can also be starting points for your own grammars.
Please, be sure to read the C examples before looking at the other languages, as these examples are simpler.