ITCS$317$ Term Project

Building a Context$-$Free Grammar Parser for a Programming Language

Due: $7$ Dec $2024$

Logo is a simple programming language that was created to help children learn

programming in the $1970$s and $1980$s

The language assumes that there is a drawing area on the screen $($see Figure $1$ right

panel$),$ and a turtle which starts at the center of the screen. The programmer then

enters a set of commands for the turtle to move on this drawing area. The

movements of the turtle leave lines on the screen, and thus create a drawing. The

language has simple programming structures for repetition $($i$.$e$.$ loops$),$ conditional

$($i$.$e$.$ if statements$),$ as well as instructions which control the pen $($or turtle$).$

A sample Logo program might look like this. This program draws a square which is

$100$ high by $100$ pixels wide.

repeat $4\{$

forward $100$;

turn right $90$;

$\}$;

The following is a probable grammar for a simple version of the Logo programming

language.

The terminals in this grammar are shown in bold $($Courier New$).$ Note that NUM

denotes any nonnegative integer number $($i$.$e$.0),$ and ID denotes any identifier

which starts with a letter from the alphabet followed by any sequence of letters or digits. NUM can be denoted by the regular expression $(0+1+2+3+4+5+6+7+8+9)+.$ ID

can be denoted by $($a$...$ z $+$A$...$Z$)+($a$...$z$+$A$...$Z$+0..\mathrm{.}9)*.$

Also note that the language is not case sensitive$,$ and that it is free$-$form so you

should ignore any whitespace in the program

program $$ statement$\_$list

statement$\_$list $$ statement $|$statement statement$\_$list

statement $$ forward expression;

$|$ backward expression;

$|$ turn right expression;

$|$ turn left expression;

$|$ while expression $\{$ statement$\_$list $\}$;

$|$ for ID $=$ expression to expression step NUM

$\{$ statement$\_$list $\}$;

$|$ pen on;

$|$ pen off;

$|$ color expression;

$|$ assignment;

assignment $$ ID $=$ base

base $$ ID $|$ NUM $|-$ NUM $|$ expression

expression $$ term

expression $$ term addOp term

term $$ factor

term $$term multOp factor

factor $$ base

addOp $+|-$

multOp $*|/|^$

Problem:

Use ANTLR to construct the lexical analyzer and parser for the grammar

given above. Then test the ANTLR code on some input with and without syntax

errors. An IDE is available for ANTLR and is called ANTLRWORKS. The IDE has an editor and can show you errors and syntax trees in a separate window. Download ANTLR$+$ANTLRWORKS version $3.$ It is a standalone Java archive that you can use for this project. You can modify the grammar above if it will work better or to eliminate any problems as long as you

keep the language accepted by the grammar the same. Your final project developed by you should be tested by inputing a code in the Logo language given above and it should inform the user whether it contains syntax errors

or not. A syntax tree should be the output for valid programs, and you can view it through ANTLRWorks GUI.

Submit the file grammar.g file after testing it on Blackboard with screenshots of the

parsing trees for an accepted case and another for the syntax error case.