G++ Interpreter

Introduction

G++ is a language my professor of Programing Languages course created for educational purposes. This project is an interpreter written for this language with yacc/bison. The properties of the language will be given below as well as some instructions for running the project. With this language you can set variables, change them, do math expressions and create loops.

Properties Of The G++ Language

General Properties

• Lisp-like syntax
• Imperative
• Static Scope
• Static Binding
• Strongly Typed

Lexical Properties

Terminal Symbols

• Keywords: and, or, not, equal, less, nil, list, append, concat, set, for, if, exit, load, disp, true, false, while, defvar.
• Operators: +, -, /, *, (, ), **
• Comments: starts with ;;
• Value: Any combination of digits with no leading zeros. 0 is considered a value.
• Identifier: Any combination of alphabetical characters and digits with no leading digit.

Tokens

Lexer will parse the code into these tokens first: COMMENT, KW_AND, KW_OR, KW_NOT, KW_EQUAL, KW_LESS, KW_NIL, KW_LIST, KW_APPEND, KW_CONCAT, KW_SET, KW_FOR, KW_IF, KW_EXIT, KW_LOAD, KW_DISP, KW_TRUE, KW_FALSE, KW_WHILE, KW_DEFVAR, OP_PLUS, OP_MINUS, OP_DIV, OP_MULT, OP_OP, OP_CP, OP_DBLMULT, OP_COMMA, STRING, OP_Q, IDENTIFIER, VALUE.

Concrete Syntax:

Here are the Backus-Naur form (BNF) rules. Notice that terminal symbols are all uppercase and non terminals are not. Below all the non-token symbols are also defined as non-terminal symbols.

• start -> start input | input.
• input -> expi | explisti | expb | COMMENT.
• listval -> OP_Q OP_OP values OP_CP | OP_OP KW_LIST values OP_CP | OP_Q OP_OP OP_CP | KW_NIL.
• values -> values VALUE | VALUE.
• start -> start input | input.
• input -> expi | explisti | expb | COMMENT.
• listval -> OP_Q OP_OP values OP_CP | OP_OP KW_LIST values OP_CP | OP_Q OP_OP OP_CP | KW_NIL.
• values -> values VALUE | VALUE.
• expi -> VALUE |
      IDENTIFIER |
      OP_MINUS expi |
      OP_OP KW_SET IDENTIFIER expi OP_CP |
      OP_OP OP_PLUS expi expi OP_CP |
      OP_OP OP_MINUS expi expi OP_CP |
      OP_OP OP_DIV expi expi OP_CP |
      OP_OP OP_MULT expi expi OP_CP |
      OP_OP OP_DBLMULT expi expi OP_CP |
      OP_OP KW_IF expb explisti OP_CP |
      OP_OP KW_IF expb expi OP_CP |
      OP_OP KW_IF expb explisti explisti OP_CP |
      OP_OP KW_IF expb expi expi OP_CP |
      OP_OP KW_WHILE OP_OP expb OP_CP explisti OP_CP |
      OP_OP KW_WHILE OP_OP expb OP_CP expi OP_CP |
      OP_OP KW_FOR OP_OP IDENTIFIER expi expi OP_CP explisti OP_CP|
      OP_OP KW_FOR OP_OP IDENTIFIER expi expi OP_CP expi OP_CP |
      OP_OP KW_DISP expi OP_CP |
      OP_OP KW_DISP explisti OP_CP |
      OP_OP KW_LOAD STRING OP_CP |
      OP_OP KW_EXIT OP_CP.
• expb -> OP_OP KW_AND expb expb OP_CP |
      OP_OP KW_OR expb expb OP_CP |
      OP_OP KW_NOT expb OP_CP |
      OP_OP KW_EQUAL expb expb OP_CP |
      OP_OP KW_EQUAL expi expi OP_CP |
      OP_OP KW_LESS expi expi OP_CP |
      KW_TRUE |
      KW_FALSE.
• explisti -> OP_OP KW_CONCAT explisti explisti OP_CP | OP_OP KW_APPEND expi explisti OP_CP | listval.

How To Compile and Run

To compile

flex gpp_lexer.l
yacc -d gpp_interpreter.y
cc lex.yy.c y.tab.c

To run

./a.out

Screenshots