lr1

问题 I'm having trouble building the collection of sets of items for LR(1) parsers with a grammar containing epsilon productions. For example, given the following grammar (where eps stands for epsilon) S -> a S U U -> b | eps State0 would be S' -> .S, $ S -> .a S U, $ Moving with 'a' from State0 would give the following state, let's call it State2 S -> a .S U, $ S -> .a S U, $/??? In order to have the lookahead for the second item of State2 I need to calculate FIRST(U$). I know that FIRST(U) = {'b

问题 I'm having trouble building the collection of sets of items for LR(1) parsers with a grammar containing epsilon productions. For example, given the following grammar (where eps stands for epsilon) S -> a S U U -> b | eps State0 would be S' -> .S, $ S -> .a S U, $ Moving with 'a' from State0 would give the following state, let's call it State2 S -> a .S U, $ S -> .a S U, $/??? In order to have the lookahead for the second item of State2 I need to calculate FIRST(U$). I know that FIRST(U) = {'b

问题 Where can I find a simple (as much as possible, but no simpler!) implementation of an LR(1) parser generator? I'm not looking for performance, just the ability to generate the LR(1) states (item sets). C++, C#, Java, and Python would all work for me. 回答1: I've written a very simple one in C# and wanted to share it here. It basically populates the action lookup table, which tells you which state to shift to or which rule to use for reduction. If the number is nonnegative, then it denotes a new

问题 I have coded a table driven LR(1) parser and it is working very well however I am having a bit of a disconnect on the stage of turing a parse into a syntax tree/abstract syntax tree. This is a project that I m very passionate about but I have really just hit a dead end here. Thank you for your help in advance. Edit: Also my parser just uses a 2d array and an action object that tells it where to go next or if its a reduction where to go and how many items to pop. I noticed that many people use

问题 For the given context free grammar: S -> G $ G -> PG | P P -> id : R R -> id R | epsilon How do I rewrite the grammar so that it is LR(1)? The current grammar has shift/reduce conflicts when parsing the input "id : .id", where "." is the input pointer for the parser. This grammar produces the language satisfying the regular expression (id:(id)*)+ 回答1: It's easy enough to produce an LR(1) grammar for the same language. The trick is finding one which has a similar parse tree, or at least from

问题 I'm trying to understand how LR1 Parsers work but I came up with a strange problem: What if the grammar contains Epsilons? For instance: if I have the grammar: S -> A A -> a A | B B -> a It's clear how to start: S -> .A A -> .a A A -> .B ... and so on but I don't know how to do it for such a grammar: S -> A A -> a A a | \epsilon Is it correct to do: S -> .A A -> .a A a ( A -> .\epsilon ) And then make this State in the DFA accepting? Any help would really be appreciated! 回答1: Yes, exactly