Hello,<div><br></div><div>I have some input which is divided up into segments like this:</div><div><br></div><div><br></div><div>[&quot;foo&quot;, &quot;hi&quot;, &quot;there&quot;, &quot;world&quot;]</div><div><br></div><div>
And I want to use parsec to parse the segments. I am looking for a way to be able to use Char parsers on each segment, but also parse the list of segments as a whole.</div><div><br></div><div><br></div><div>I have an implementation which works, but I am not feeling that satisfied with it. An example parser looks like this:</div>
<div><br></div><div><div>testp :: GenParser String () (Char, String, String)</div><div>testp =  </div><div>  do segment &quot;foo&quot;</div><div>     st &lt;- p2u (char &#39;h&#39; &gt;&gt; char &#39;o&#39;)</div><div>     sg &lt;- anySegment</div>
<div>     sg&#39; &lt;- anySegment</div><div>     return (st,sg, sg&#39;)</div><div><br></div><div>If you use it to parse [&quot;foo&quot;, &quot;hi&quot;, &quot;there&quot;, &quot;world&quot;] you get:</div><div><br></div>
<div><div>*Main&gt; test</div><div>[&quot;foo&quot;,&quot;hi&quot;,&quot;there&quot;,&quot;world&quot;] (segment 2 character 2): </div><div>unexpected &quot;i&quot;</div><div>expecting &quot;o&quot;</div><div><br></div><div>
This is good -- the error tells you the segment and the offset. The combinators, segment and anySegment match on String tokens. The p2u function converts a Char parser into a String parser.</div><div><br></div><div>The primary issue is that I can not figure out how to implement p2u so that it works under Parsec 2 and 3 with out changes. </div>
<div><br></div><div>The secondary issue is that I feel like the DSL is not that great. I would rather write the above parser like this:</div><div><br></div><div><div>testp :: GenParser String () (Char, String, String)</div>
<div>testp =  </div><div>  do string &quot;foo&quot;</div><div>       nextSegment</div><div>       char &#39;h&#39; &gt;&gt; char &#39;o&#39;</div><div>       nextSegment</div><div>       sg &lt;- many anyChar</div><div>       nextSegment</div>
<div>       sg&#39; &lt;- many anyChar</div><div>       return (st,sg, sg&#39;)</div><div><br></div><div>so, the combinators like &#39;many&#39; would only see to the end of the current segment. nextSegment would bring the next segment into context (or possibly fail if the current segment was not completely consumed). I could also, perhaps, reimplement anySegment as:</div>
<div><br></div><div>anySegment =</div><div>   do s &lt;- many anyChar</div><div>        nextSegment</div><div>        return s</div><div><br></div><div>and write:</div><div><br></div><div><div>testp :: GenParser String () (Char, String, String)</div>
<div>testp =  </div><div>  do string &quot;foo&quot;</div><div>       nextSegment</div><div>       char &#39;h&#39; &gt;&gt; char &#39;o&#39;</div><div>       nextSegment</div><div>       sg &lt;- anySegment</div><div>       sg&#39; &lt;- anySegment</div>
<div>       return (st,sg, sg&#39;)</div><div><br></div></div><div>I don&#39;t see a way to implement this on top of parsec though.</div><div><br></div><div>Am I missing some clever ideas here?</div><div><br></div><div>I have attached my code that implements the first method. Any ideas how to make it parsec 2/3 agnostic ? The primary issue is that if I use runParser on the inner Char parser, I need some way to stick a ParseError back into the parent context (with out just converting it to a String and calling fail). I can see how to get/set the inputState, etc, in a portable way, but I don&#39;t see how to set the ParseError in a portable way.The attached code requires 3.1.0 because it uses mkPT / runParsecT :(</div>
<div><br></div><div>thanks!</div><div>- jeremy</div><div><br></div><div><br></div></div></div></div>