212 questions
1
vote
1
answer
139
views
How to Handle Left Associativity for Logical Operators in a Recursive Descent Parser?
I'm implementing a recursive descent parser for a mini-shell program based on bash, where typically, right recursion is applied. However, for logical operators && and ||, this approach doesn't ...
- 93
0
votes
1
answer
81
views
Errors on Recursive Descent Parsing Java
I am working on this java program, which is a recursive descent parser. The output provided below does not contain any syntax errors, however the program printing an error message. The program should ...
- 13
1
vote
2
answers
321
views
Python selenium: nested element finding
I'm trying to write a function, which returns a list of elements from any level of nesting from the html, containing the word 'products' in its text, case insensitive.
here is my function:
def ...
0
votes
1
answer
79
views
tokenizer and parser returns wrong answer for a postfix notation
I have coded a tokenizer and a recursive parser for a postfix expression. My code is the following:
import re
token_patterns = [
('OPERATOR', r'[+\-*/]'),
('NUMBER', r'\d+'),
('WHITESPACE'...
- 3,477
0
votes
1
answer
89
views
Discriminating between a Lambda Parameter List and a Grouping Expression in a Recursive Descent Parser
I am writing a small scripting language for a project I am working on. I wrote a simple recursive-descent parser for it (similar to the one in the Crafting Interpreters). I wanted to add support for ...
0
votes
0
answers
186
views
Evaluating Logical Operations AND, OR, NOT dynamically in Java
I have a requirement to execute dynamic expressions for the input data (Map) using Java Code.
For Example,
Condition -
EmployeeShift = 'General' AND (EmployeeType = 'CONTRACT' OR Designation IN 'ADMIN'...
- 15
-1
votes
1
answer
176
views
Recursive sub to determinate level of items in BOM
In the next sample structure BOM:
updated screenshot
we find articles, and further down we find their structure with its content, other articles which in their turn may or may not have their content ...
- 3
0
votes
0
answers
45
views
What are the criteria for determining if a language can be parsed using recursive descent parsing?
How do i know if a language can be parsed by recursive descent parsing?
For example, how would i go about determining whether this language can be parsed in that manner:
Language = { s^p r^q | p > ...
- 11
0
votes
1
answer
142
views
languages parsed with recursive descent
I was wondering what makes languages possible to be parsed with recursive descent. for example we have 5 languages over {x,y,r}:
A = { x^n y^n | n <= k }
B = { x^n y^k | n > k }
C = { x^k y^n | ...
- 23
1
vote
0
answers
140
views
Context Free Grammar clarification
I created the following grammar for a minishell, but i realized that the parser never goes to command_p, it only stays at cmd_prefix.
Can somebody please clarify for me since i've seen a similar ...
- 11
0
votes
1
answer
364
views
Recursive descent parser from BNF grammar in java
I need to make a recursive descent parser that follows the grammar
<program> → <statements>
<statements>→ <statement> | <statement><semi_colon><statements>
&...
- 31
0
votes
1
answer
49
views
Removing left recursion from JSF*ck grammar rules
I am trying to figure out a JSF*uck grammar. I read the actual JavaScript grammar here and only took the grammar rules that were relevant to JSF*ck and got this:
Expression: AdditiveExpression ;
...
- 710
1
vote
1
answer
327
views
How can I transform this into a recursive descent parser
My code is a follows (this code 100% works, it just doesn't use recursive descent)
import java.awt.Component;
import java.awt.FlowLayout;
import java.awt.GridLayout;
import java.io.File;
import java....
- 13
2
votes
1
answer
353
views
MongoDB javascript `"$function"` not returning expected value in mongoplayground.net
N.B.: This is the first javascript function I've written. My question is inspired by another question inquiring about recursive descent within a MongoDB document.
I tried the function on jsfiddle.net ...
- 12k
0
votes
0
answers
126
views
Verifying if an expression conforms to restrictive context-free grammar
I'm trying to write a parser that accepts a toy language for a software project class. Part of the production rules relevant to the question in EBNF-like syntax is given here (there's way more ...
- 63
1
vote
0
answers
457
views
Converting W3C's EBNF to BNF
Following up on
Converting EBNF to BNF, which has a rule of:
From EBNF to BNF
For building parsers (especially bottom-up) a BNF grammar is often better, than EBNF. But it's easy to convert an EBNF ...
- 23.6k
0
votes
0
answers
189
views
How to make recursive descent parsing recognise expressions
I am making a graphing calculator and the issue I am having is finding a way to take in inputs like sin(90) and run my function for sin that I coded into another file.
I am using a recursive descent ...
- 1
0
votes
0
answers
481
views
Types of Top down parsers
I want to clearly classify top down parsers. After reading lot of resources, i am connecting the dots.
I concluded following -
There are 2 types of top down parsers -
One that uses backtracking
...
- 25
0
votes
1
answer
420
views
The token was already consumed by another rule, Can't parse the token again
I am constructing an LL(1) parser (Recursive Descent Parser) and I need to parse the sentence a = 3, I have two procedures to match that rule: parse_assignment and parse_binary_operator,
each function ...
- 1,937
0
votes
2
answers
402
views
Recursive-descent parser
The question is to write a recursive-descent parser for a language that contains sentences of form w+w', in which w is an arbitrary string of lowercase chars, w' is the reverse of w, and + the plus ...
- 11
1
vote
1
answer
365
views
K&R dcl program detects almost nothing
I've been stuck with the dcl program from chapter 5.12 in K&R C. It is basically a program which accepts a C variable/function/table declaration and prints a description of it in English. It works ...
- 21
0
votes
1
answer
61
views
Invalid grammar for a top-down recursive parser
I am trying to create grammar for a naive top-down recursive parser. As I understand the basic idea is to write a list of functions (top-down) that correspond to the productions in the grammar. Each ...
- 1,004
0
votes
1
answer
165
views
Realize precedence climbing in Haskell
I am trying to realise precedence climbing in Haskell, following this specific algorithm:
compute_expr(min_prec):
result = compute_atom()
while cur token is a binary operator with precedence >= ...
- 47
3
votes
2
answers
1k
views
How to construct tree pattern matching algorithm in JavaScript?
Okay this is a bit of an involved question, but tl;dr it's basically how do you parse an "actual tree" using a "pattern tree"? How do you check if a particular tree instance is ...
- 80.5k
0
votes
0
answers
99
views
Recursive descend parser for evalutating math expressions throws an error and I do not how to fix it
I'm new here and have a generall question. I'm trying to create a recursive descent parser for the evaluation of mathematic expressions, and the parser I have crafted until now also works very good ...
- 1
0
votes
2
answers
98
views
Please, help me to understand parsing trees example from craftinginterpreters.com
I'm trying to build a C compiler from scratch. Googling took me to the https://craftinginterpreters.com/ site. There are a lot of explanations how source code parsers work in detail. I've reached &...
- 1,899
0
votes
1
answer
844
views
Recursive descent parser - dealing with closing brackets
I'm trying to build a recursive descent parser that builds an AST as it goes. The language is fairly simple;
x >/</= y #x, y can be any letter/number, matched by regex.
Then, AND/OR with ...
- 461
1
vote
1
answer
231
views
StringTokenizer replacement in Java
I'm trying to write a recursive descent parser. I need a method that converts the string to a stream, so I can use a next method. Everywhere I read, it says that StreamTokenizer is outdated and ...
- 461
0
votes
0
answers
70
views
An erroneous successful parsing in a recursive descent parser
I have the following code. It's a recursive descent parser with backtracking.
/*\ /*\
|*|--------------|*|
|*| Grammar: |*|
|*| A -> ( A ) B |*|
|*| | [ A ] B |*|
|*| | n B ...
- 25
2
votes
1
answer
682
views
Parsing nested parentheses in F# using recursive descent
I'm trying to make a recursive descent parser in F#. I looked at http://www.fssnip.net/bM but this type of parser uses a string instead of a list.
I'm struggling with parsing parentheses, and ...
- 45
0
votes
1
answer
103
views
Does a Recursive Predictive Descent Parser NEEDS to construct a complete syntax tree and store in memory?
I've been thinking and a question has arisen. Does this type of compiler really need the complete syntax tree in memory?
- 1
0
votes
1
answer
288
views
Cannot get LL(1) form of grammar for recursive descent parser
I have grammar:
S -> bU | ad | d
U -> Ufab | VSc | bS
V -> fad | f | Ua
To contruct recursive descent parser I need LL(1) form.
Best I got is:
S -> bU | ad | d
U -> fY | bSX
Y -> ...
- 35
1
vote
0
answers
216
views
Eliminating left recursion from function call parsing
First of all, I know there are a lot of answers and resources already available regarding this topic. However, I'm having a really hard time understanding the grammar notation that is often used in ...
- 133
0
votes
1
answer
190
views
How can I simplify a recursive-descent parser?
I have the following simple LL(1) grammar, which describes a language with only three valid sentences: "", "x y" and "z x y":
S -> A x y | ε .
A -> z | ε .
I have ...
- 14.5k
-1
votes
1
answer
59
views
Parsing procedure calls for a toy language
I have a certain toy language that defines, amongst others, procedures and procedure calls, using EBNF syntax:
program = procedure, {procedure} ;
procedure = "procedure", NAME, bracedblock ;
...
- 312
1
vote
2
answers
425
views
Parser/Grammar: 2x parenthesis in nested rules
Despite my limited knowledge about compiling/parsing I dared to build a small recursive-descent parser for OData $filter expressions. The parser only needs to check the expression for correctness and ...
- 384
0
votes
1
answer
808
views
Recursive descent Parser: infix to RPN [2]
this the continuation of me trying to make a recursive descent parser--LL(1)-- that takes in infix expressions and outputs RPN. Here is a link to my first question to which @rici did an amazing job of ...
- 366
0
votes
1
answer
1k
views
Recursive descent: infix to postfix conversion repeating operators
We recently learned about converting infix to postfix using stacks during our programming course at uni. And I have meaning to write my parser for a while, so I decided to it using recursive descent. ...
- 366
0
votes
1
answer
970
views
How does gcc/clang parse c++ if it can't be parsed by a LR(1) parser?
GCC/Clang are handwritten parsers. I read a post saying that C++ can't be parsed by an LR(1) parser (Why can't C++ be parsed with a LR(1) parser?). If so, how come GCC/Clang are handwritten ...
- 3,305
0
votes
0
answers
393
views
LALR parser being slower than recursive descent parser
Recently I wrote a (highly optimized) LALR(1) parser (that could handle ambiguous grammars) and supplied it a very ambiguous grammar. After that, I wrote a recursive descent parser for the same ...
- 3,305
2
votes
0
answers
227
views
How to rewrite this grammar for LL(1) parsing?
I am trying to write a top-down recursive-descent parser for a small language, and I am facing some issues with the assignment statements. Here is the grammar from the language specifications:
<...
- 2,293
0
votes
0
answers
469
views
Writing a recursive descent parser with nested if-conditions
I am writing a recursive descent parser for parsing a specific grammar, and I have to do the nested if/else in that grammar.
The grammar is as follows:
<statement> ::= if <cond> <...
-1
votes
1
answer
276
views
Accepting an Equal Sign using Recursive Descent Parsing in C
I am currently trying to build a recursive descent parser that parses assignment statements such as a = 4 + b. The grammar looks as follows
<stmt> → id = <expr>
<expr> → <term>...
- 356
1
vote
1
answer
134
views
How to write code for part of a recursive descent parser? [duplicate]
I'm looking for an answer to this Stack Overflow question: Can somebody walk me through what this question is trying to ask of me?
It asks to do the following, as the person who replied to it explains:...
user12875544
0
votes
1
answer
59
views
Partition the upper part for the given key
I would like to implant recursive search using python, it will partition the upper part for the given key
example: list[2, 4, 6, 9, 10]
for the key is 6 case, the return index is 3
for the key is 4 ...
1
vote
1
answer
114
views
Can somebody walk me through what this question is trying to ask of me?
The following programming languages question seems really unclear and what it wants me to do is not obvious to me, could somebody help me to understand it?
The question:
Implement part of a ...
- 127
7
votes
1
answer
2k
views
Difference between a PEG and recursive descent parser?
I have recently come across PEG parsers, and Guido van Rossum's article on PEG parsers and how to construct them. That article talks about "PEG" parsers but internally it looks exactly like ...
- 1,157
0
votes
0
answers
176
views
What About Abstract Syntax Tree Recursivity In Javascript?
I am trying to build a compiler in javascript and until now I've managed to build a lexer that creates tokens based on input:
= Test Input (with optional semicolon):
data myVariable = 4
data ...
- 124
2
votes
1
answer
2k
views
Understanding this implemented recursive-descent parser in Haskell
I had an assignment problem were I had to parse a tokenized prefix calculator notation on a pre-defined AST. We were given a pretty complete algorithm for parsing (we had to add some stuff).
The ...
- 47
2
votes
1
answer
557
views
Infinite recursion for parsing arithmetic expressions using a recursive descent parser
I am trying to create my own recursive descent parser in python, but when my parser runs into a rule concerning arithmetic expressions, it surpasses the python recursion limit. Here is the grammar:
...
- 1,157