Using JFlex and Byacc/J, write a parser that can determine valid English sentences according to the grammar below.

sentence -> nphrase VERB ending

| nphrase VERB vmodifier ending

| nphrase VERB nphrase ending

;

ending -> PUNCT END

;

nphrase -> modifiednoun

| ARTICLE modifiednoun

;

modifiednoun -> NOUN

| nmodifier modifiednoun

;

nmodifier -> ADJECTIVE

| ADVERB nmodifier

;

vmodifier -> ADVERB

| ADVERB vmodifier

| PREPOSITION nphrase

;

The only allowed tokens are ARTICLE VERB NOUN ADJECTIVE ADVERB PREPOSITION END PUNCT

END = newline

PUNCT = period, comma, exclamation, question mark

ARTICLE = the, The, an, An, a, A (both lower, upper case for first character only)

VERB = study, sleep, play, throw, write, eat

NOUN = book, laptop, candy, pen, box

ADJECTIVE = cute, clever, smart, witty, tired, blue, red

ADVERB = willfully, abruptly, endlessly, delightfully, lightly, beautifully

PREPOSITION = before, into, on, above, by, along

JFLEX STARTING CODE:

%% %class Scanner %unicode %line %column %byaccj %{ /* return the current line number.*/ public int getLine() { return yyline; } public int getColumn() { return yycolumn; } %} %% b { return Parser.b; } c { return Parser.c; } . { System.out.println("No match: "+yytext()); } 

BYACC STARTING CODE:

%{ import java.io.*; import java.util.*; /* All of the below productions that do not have associated actions are using the DEFAULT action -- $$ = $1 */ %} %token b c %start S %% S: B C { System.out.println("Prod1"); } ; B: b B { System.out.println("Prod2"); } | b { System.out.println("Prod3"); } ; C: c { System.out.println("Prod4"); } ; %% /* Byacc/J expects a member method int yylex(). We need to provide one through this mechanism. See the jflex manual for more information. */ /* reference to the lexer object */ private Scanner lexer; /* interface to the lexer */ private int yylex() { int retVal = -1; try { retVal = lexer.yylex(); } catch (IOException e) { System.err.println("IO Error:" + e); } return retVal; } /* error reporting */ public void yyerror (String error) { System.err.println("Error : " + error + " at line " + lexer.getLine() + " column: " + lexer.getColumn()); } /* constructor taking in File Input */ public Parser (Reader r) { lexer = new Scanner (r); } public static void main (String [] args) throws IOException { Parser yyparser = new Parser(new FileReader(args[0])); yyparser.yyparse(); }