4e19ab9fcd
Currently when --defines is used, we generate a header, and paste an exact copy of it into the generated parser implementation file. Let's provide a means to #include it instead. We don't do it by default because of the Autotools' ylwrap. This program wraps invocations of yacc (that uses a fixed output name: y.tab.c, y.tab.h, y.output) to support a more modern naming scheme (dir/foo.y -> dir/foo.tab.c, dir/foo.tab.h, etc.). It does that by renaming the generated files, and then by running sed to propagate these renamings inside the files themselves. Unfortunately Automake's Makefiles uses Bison as if it were Yacc (with --yacc or with -o y.tab.c) and invoke bison via ylwrap. As a consequence, as far as Bison is concerned, the output files are y.tab.c and y.tab.h, so it emits '#include "y.tab.h"'. So far, so good. But now ylwrap processes this '#include "y.tab.h"' into '#include "dir/foo.tab.h"', which is not guaranteed to always work. So, let's do the Right Thing when the output file is not y.tab.c, in which case the user should %define api.header.include. Binding this behavior to --yacc is tempting, but we recently told people to stop using --yacc (as it also enables the Yacc warnings), but rather to use -o y.tab.c. Yacc.c is the only skeleton concerned: all the others do include their header. * data/skeletons/yacc.c (b4_header_include_if): New. (api.header.include): Provide a default value when the output is not y.tab.c. * src/parse-gram.y (api.header.include): Define.
Examples in C
This directory contains simple examples of Bison grammar files in C.
Some of them come from the documentation, which should be installed together with Bison. The URLs are provided for convenience.
rpcalc - Reverse Polish Notation Calculator
The first example is that of a simple double-precision Reverse Polish Notation calculator (a calculator using postfix operators). This example provides a good starting point, since operator precedence is not an issue.
Extracted from the documentation: "Reverse Polish Notation Calculator" https://www.gnu.org/software/bison/manual/html_node/RPN-Calc.html
calc - Simple Calculator
This example is slightly more complex than rpcalc: it features infix
operators (1 + 2, instead of 1 2 + in rpcalc), but it does so using a
unambiguous grammar of the arithmetic instead of using precedence
directives (%left, etc.).
mfcalc - Multi-Function Calculator
A more complete C example: a multi-function calculator. More complex than the previous example. Using precedence directives to support infix operators.
Extracted from the documentation: "Multi-Function Calculator: mfcalc". https://www.gnu.org/software/bison/manual/html_node/Multi_002dfunction-Calc.html
lexcalc - calculator with Flex and Bison
The calculator, redux. This time using a scanner generated by Flex.
reccalc - recursive calculator with Flex and Bison
The example builds on top of the previous one to provide a reentrant parser.
Such parsers can be called concurrently in different threads, or even
recursively. To demonstrate this feature, expressions in parentheses are
tokenized as strings, and then recursively parsed from the parser. So
(((1)+(2))*((3)+(4))) uses eight parsers, with a depth of four.