Introduction

This programming project implements a simple parser for an EBNF (Extended Backus-Naur Form) grammar.

The first objective is to provide a simple example of EBNF grammar and a parser, so that students may understand the concept. The second objective is to reuse this code to do the parsing stage in the BARES programming project.

Information on EBNF grammar may be found here.

Information on recursive descendent parsing may be found here.

The Grammar

The gramar we want to parse represents arithmetic expressions with addition and subtraction of integers.

<expr>            := ("("),<term>,{ ("+"|"-"|"*"|"/"|"%"|"^"),<term>,(")") };
<term>            := <integer>;
<integer>         := 0 | ["-"],<natural_number>;
<natural_number>  := <digit_excl_zero>,{<digit>};
<digit_excl_zero> := "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9";
<digit>           := "0"| <digit_excl_zero>;

This grammar accepts expressions like:

• "13 + 39 - 0 + -14 / 2"
• " 19"
• "-11 % -8"
• " -54"
• "-21 * (23 + 1234)"
• "3 + 3 * 3 % 4"
• "(3^5) % 10"

And rejects expressions like:

• "01 + 3"
• " - 3 + 4"
• "2 + "
• " "
• "(+2 + 5"
• "2 + 4)"
• "2/0"
• "1000000000 - 1"
• ""

Compiling

To compiling this project is necessary access, in terminal, the repository. After that write, in terminal, the command :

make

Running

To execute is necessary write the follow command :

./parser archive_list_of_expression_name.* .

The char '*' refer to a text type of an expression archive.

Limitations

This BARES don't accept more than one unary '-'. Only numbers and final results of expression beetwen the range [−32,768, +32,767] are accepted (The types has been defined in bares.cpp and main.cpp).

Authorship

Program developed by Erick de Oliveira Silva ([email protected]), graduation student of IT in UFRN.

Contributors

In Parser and Token codes has some contribuiton of Selan ([email protected]) and students from LP1, 2017.1 with the codes writed in LP1 classes.

© IMD/UFRN 2017.1