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PORepresenting statement-terminating newlines in a grammar?
 

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    <p>A lot of programming languages have statements terminated by line-endings. Usually, though, line endings are allowed in the middle of a statement if the parser can't make sense of the line; for example, </p> <pre><code>a = 3 + 4 </code></pre> <p>...will be parsed in Ruby and Python* as the statement <code>a = 3+4</code>, since <code>a = 3+</code> doesn't make any sense. In other words, the newline is ignored since it leads to a parsing error.</p> <p>My question is: how can I simply/elegantly accomplish that same behavior with a tokenizer and parser? I'm using Lemon as a parser generator, if it makes any difference (though I'm also tagging this question as yacc since I'm sure the solution applies equally to both programs).</p> <p>Here's how I'm doing it now: allow a statement terminator to occur optionally in any case where there wouldn't be syntactic ambiguity. In other words, something like</p> <pre><code>expression ::= identifier PLUS identifier statement_terminator. expression ::= identifier PLUS statement_terminator identifier statement_terminator. </code></pre> <p>... in other words, it's ok to use a newline after the plus because that won't have any effect on the ambiguity of the grammar. My worry is that this would balloon the size of the grammar and I have a lot of opportunities to miss cases or introduce subtle bugs in the grammar. Is there an easier way to do this? </p> <p>EDIT*: Actually, that code example won't work for Python. Python does in fact ignore the newline if you pass in something like this, though:</p> <pre><code>print (1, 2, 3) </code></pre>
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