ebnfValidator

A brute force parser for any kind of EBNF grammar that validates whether a partiular code snippet is syntactically valid or not. The parser uses a top-down approach and evaluates all possible productions.

The syntax for EBNF grammar is adjusted to correspond to the one used in the course Introduction to Programming at ETH Zurich.

As the parser could get trapped in infinite recursion, the search for a valid production is stopped after a maximum level of depth, which can lead to incorrect results for heavily nested productions.

For more context and background, see here

Installation

mkdir $HOME/ebnfValidator
curl https://raw.githubusercontent.com/svensglinz/ebnfValidator/master/ebnfValidator.jar > $HOME/ebnfValidator/ebnfValidator.jar
# echo "alias ebnfValidator='java -jar $HOME/ebnfValidator/ebnfValidator.jar' >> ~/.bashrc

Uninstall

rm -r $HOME/ebnfValidator
# remove alias from ~/.bashrc if it was set

Usage

First, create a text file that describes your grammar.

• Each rule name must be wrapped in <>
• Each line consists of one rule in the form of <= RULE DESCRIPTION
• each description can contain: literals, repetition {}, option [] or selection |
• selection has the highest precedence before all other operators
  
  eg: <RULE1> <= a <RULE1> | b is parsed as <RULE1> <= (a <RULE1> ) | b (ie. as a selection between a AND or b
• The entry point into the grammar is always a rule called expression. If you do not have this rule ( or it is not the top-level rule), the results will be incorrect
• If your grammar contains literals that are reserverd characters ()|{}[]<=, you need to wrap them in quotes
• The empty sequence can be specified as ""

LIMITATIONS:

• literals (eg. b in the following) can only be added individually
  
  Eg. If you want a grammar such as <STRING> <= {<CHARACTER>} where <CHARACTER> can be any letter in the alphabet, you will have to list each letter separately ie: <CHARACTER> <= a | b | c | ... | z

For an example, see here

Then evaluate any expression against your grammar in the interactive shell

ebnfValidator grammar.txt

Welcome to the Interactive Shell! Type in any expression and check if matches against the provided Grammar Description Type '.exit' to quit at any time.

a = 100

✔️ valid

b <- 123

✔️ valid

b == 123

❌ invalid

.exit

Goodbye!