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• chomsky hierarchy and programming languages

  - by dader51

  Hi, I'm trying to learn some aspects of the CH ( chomsky hierarchy ) which are related to PL ( programming languages ), and i still have to read the Dragon Book. I've read that most of the PL can be parsed as CFG ( context free grammar ). In term of computational power, it equals the one of a pushdown non deterministic automaton. Am I right ? If it's true, then how could a CFG holds a UG ( unrestricted grammar, which is turing complete ) ? I'm asking because, even if PL are CFG they are actually used to describe TM (turing machines ) and through UG. I think that's because of at least two different levels of computing, the first, which is the parsing of a CFG focuses on the syntax related to the structure ( representation ? ) of the language, while the other focuses on the semantic ( sense, interpretation of the data itself ? ) related to the capabilities of the pl which is turing complete. Again, are these assumptions rights ? thanx a lot.

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• Theory of formal languages - Automaton

  - by dader51

  Hi everybody ! I'm wondering about formal languages. I have a kind of parser : It reads à xml-like serialized tree structure and turn it into a multidimmensionnal array. I figured out that i need at least three variables to achieve the job : $tree = array(); // a new array $pTree = array(&$tree); // a new array which the first element points to $tree; $deep = 0; plus the one containing the sentence splitted into words. My point is on the similarities between the algorithm deing used and the differents kinds of automatons ( state machines turing machines stack ... ). The $words variable is the "tape" of the automaton, the test/conditions of the algorithm are transitions, $deep is the state and $tree is the output. I cannont figure what is $pTree. So the question is : which is the automaton I implictly use here, and to which formal languages family does it fit ? And what's about recursion ?

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• regex and javascript, some matches disappear !

  - by dader51

  Here is the code : > var reg = new RegExp(" hel.lo ", 'g'); > > var str = " helalo helblo helclo heldlo "; > > var mat = str.match(reg); > > alert(mat); It alerts "helalo, helclo", but i expect it to be "helalo, helblo, helclo, heldlo" . Only the half of them matches, I guess that's because of the space wich count only once. So I tried to double every space before processing, but in some case it's not enough. I'm looking for an explanation, and a solution. Thx

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