context-free-grammar

I'm trying to learn about shift-reduce parsing. Suppose we have the following grammar, using recursive rules that enforce order of operations, inspired by the ANSI C Yacc grammar : S: A; P : NUMBER | '(' S ')' ; M : P | M '*' P | M '/' P ; A : M | A '+' M | A '-' M ; And we want to parse 1+2 using shift-reduce parsing. First, the 1 is shifted as a NUMBER. My question is, is it then reduced to P, then M, then A, then finally S? How does it know where to stop? Suppose it does reduce all the way to S, then shifts '+'. We'd now have a stack containing: S '+' If we shift '2', the reductions might

I have the following grammar: S → a S b S | b S a S | ε Since I'm trying to write a small compiler for it, I'd like to make it LL(1). I see that there seems to be a FIRST/FOLLOW conflict here, and I know I have to use substitution to resolve it, but I'm not exactly sure how to go about it. Here is my proposed grammar, but I'm not sure if it's correct: S-> aSbT | epsilon T-> bFaF| epsilon F-> epsilon Can someone help out? templatetypedef In his original paper on LR parsing , Knuth gives the following grammar for this language, which he conjectures "is the briefest possible unambiguous grammar

I am trying to write a grammar for a set of sentences and using Pyparsing to parse it. These sentences tell what and how to search in a text file, and I need to convert them into corresponding regex search codes. However, there are some elements that are not really context-free and hence, I am finding it difficult to write production rules for them. Basically, my aim is to parse these sentences and then write regexes for them. Some examples of context-sensitive elements found in these sentences - LINE_CONTAINS phrase1 BEFORE {phrase2 AND phrase3} means in the line, phrase1 can come anywhere

I am trying to figure out how to construct a CFG (context free grammar) based on a given regular expression. For example, a(ab)*(a|b) I think there is an algorithm to go through, but it is really confusing. here is what i got so far: S->aAB; A->aAb|empty; B->a|b; Does this look right? Any help would be appreciated. Construct the CFG in three parts, each for a , (ab)* and (a|b) . For (a|b) , you've got B -> a | b right. (ab)* would mean strings like ab , abab , ababab and so on. So A -> abA | empty would be the correct production. Hence, the full grammar becomes: S -> aAB A -> abA | empty B ->

What algorithm do you use to enumerate the strings generated by a context-free grammar? It seems doable when there is no recursion, but I can't figure out how to do it in the general case, which might contain all kinds of (possibly indirect) recursion. (I'm not looking for an esoteric solution like the one on this page ; I'm looking for an algorithm that I could map to standard imperative code.) Here's an obvious but somewhat inefficient algorithm: Construct R, the Earley parser for the grammar. For each string S in A* (A is the alphabet for the grammar): If R recognizes S: Output S Here I