Bison 3.8.1

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• The Bison parser detects a syntax error (or parse error) whenever it reads a token which cannot satisfy any syntax rule.

• The prototypes are only indications of how the code produced by Bison uses yyerror. Bison-generated code always ignores the returned value, so yyerror can return any type, including void.

• void is preferable since it more accurately describes the return type for yyerror.

• This is a terminal symbol that is always defined (you need not declare it) and reserved for error handling.

• an error followed by a newline makes a valid addition to any stmts.

• Note that discarded symbols are possible sources of memory leaks, see Freeing Discarded Symbols, for a means to reclaim this memory

• These functions will be defined in the epilogue, but the parser calls them so they must be declared in the prologue.

• If the token kind is a character literal, then its numeric code is that of the character; you can use the same character literal in the lexical analyzer to express the number. If the token kind is an identifier, that identifier is defined by Bison as a C enum whose definition is the appropriate code. In this example, therefore, NUM becomes an enum for yylex to use.