LOLCODE

The goal of this assignment is to implement a LL1 Parser for a subset of the esoteric language called LOLCODE. This language is simple enough that you will not need advanced lookahead. Your parser will use the ANTLR4 lexer to generate a token stream, which can then be used to generate an AST. You must also create an interpreter for LOLCODE by walking your AST using a visitor pattern.

Your parser must do basic error detection, but it need not do error recovery, i.e. it does not need to try to continue parsing once an error is encountered. While your ANTLR4 grammar file only needs lexical rules defined, you may find it helpful to also write the parser rules that you will implement. You are allowed to use any internal AST representation that you wish. It does not need to be persisted, since the in-memory representation is all that is needed for the interpreter.

The canonical “Hello World” program in LOLCODE is:

HAI  BTW Our first program!
    VISIBLE "Hello Wurld, LOL!"
KTHXBYE

This snippet reveals important basic principles of the language:

LOLCODE is imperative (statement oriented)
LOLCODE is block structured as seen by the HAI/KTHXBYE bracketing.
white space is not important, except that newline is used as a statement terminator

As a more interesting example, the following LOLCODE program implements the simple “Guessing Game”:

HAI
    I HAS A answer ITZ 42
    I HAS A guess
    VISIBLE "Has guess?"

    OBTW infinite loop TLDR
    IM IN YR loop
       GIMMEH guess                  BTW input is a string
       MAEK guess A NUMBR            BTW cast

       BOTH SAEM guess AN answer, O RLY?
          YA RLY
              VISIBLE "Score!"
              GTFO                   BTW break
          MEBBE BOTH SAEM guess AN SMALLR OF guess AN answer
              VISIBLE "Moar!"
          NO WAI                     BTW else
              VISIBLE "2 Much!"
       OIC
    IM OUTTA YR loop
 KTHXBYE

Our simplified version of LOLCODE has integer and string variables, conditionals, loops, I/O, and various integer expressions. The full version of LOLCODE has file I/O, functions, and more advanced expressions and operations. We provide the simplified spec in this document, however, it is derived from the full spec at <https://lolcode.org>, which you may find adds additional context.

Language Specification

Implementation