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copied!<p>One major difference is that ANTLR generates an LL(*) parser, whereas YACC and Bison both generate parsers that are LALR. This is an important distinction for a number of applications, the most obvious being operators:</p> <pre><code>expr ::= expr '+' expr | expr '-' expr | '(' expr ')' | NUM ; </code></pre> <p>ANTLR is entirely incapable of handling this grammar as-is. To use ANTLR (or any other LL parser generator), you would need to convert this grammar to something that is not left-recursive. However, Bison has no problem with grammars of this form. You would need to declare '+' and '-' as left-associative operators, but that is not strictly required for left recursion. A better example might be dispatch:</p> <pre><code>expr ::= expr '.' ID '(' actuals ')' ; actuals ::= actuals ',' expr | expr ; </code></pre> <p>Notice that both the <code>expr</code> and the <code>actuals</code> rules are left-recursive. This produces a much more efficient AST when it comes time for code generation because it avoids the need for multiple registers and unnecessary spilling (a left-leaning tree can be collapsed whereas a right-leaning tree cannot). </p> <p>In terms of personal taste, I think that LALR grammars are a lot easier to construct and debug. The downside is you have to deal with somewhat cryptic errors like shift-reduce and (the dreaded) reduce-reduce. These are errors that Bison catches when generating the parser, so it doesn't affect the end-user experience, but it can make the development process a bit more interesting. ANTLR is generally considered to be easier to use than YACC/Bison for precisely this reason.</p>

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