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Bison 1.875

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Conditions for Using Bison

As of Bison version 1.24, we have changed the distribution terms for yyparse to permit using Bison's output in nonfree programs when Bison is generating C code for LALR(1) parsers. Formerly, these parsers could be used only in programs that were free software.

The other GNU programming tools, such as the GNU C compiler, have never had such a requirement. They could always be used for nonfree software. The reason Bison was different was not due to a special policy decision; it resulted from applying the usual General Public License to all of the Bison source code.

The output of the Bison utility--the Bison parser file--contains a verbatim copy of a sizable piece of Bison, which is the code for the yyparse function. (The actions from your grammar are inserted into this function at one point, but the rest of the function is not changed.) When we applied the GPL terms to the code for yyparse, the effect was to restrict the use of Bison output to free software.

We didn't change the terms because of sympathy for people who want to make software proprietary. Software should be free. But we concluded that limiting Bison's use to free software was doing little to encourage people to make other software free. So we decided to make the practical conditions for using Bison match the practical conditions for using the other GNU tools.

This exception applies only when Bison is generating C code for a LALR(1) parser; otherwise, the GPL terms operate as usual. You can tell whether the exception applies to your `.c' output file by inspecting it to see whether it says "As a special exception, when this file is copied by Bison into a Bison output file, you may use that output file without restriction."


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