4310 CS Programming Exercise Building a Parser
Due Date: Midnight, Monday, Oct 23 Using bison, you are to write a parser for a subset of Pascal. A grammar for this language appears below: start block procdcls procdcl parmlist parms parm variables vardcls vardcl idlist type stype stmtlist stmt writestmt procstmt ifstmt wstmt cmpdstmt astmt optexplist explist exp ::= ::= ::= ::= program ID ; block . variables procdcls cmpdstmt procdcls procdcl | <empty string> procedure ID parmlist ; block ; | function ID parmlist : stype ; block ; ::= ( parms ) | <empty string> ::= parms ; parm | parm ::= var vardcl | vardcl ::= var vardcls | <empty string> ::= vardcls vardcl ; | vardcl ; ::= idlist : type ::= idlist , ID | ID ::= array [ integer_constant .. integer_constant ] of stype | stype ::= integer | char | boolean ::= stmtlist ; stmt | stmt ::= ifstmt | wstmt | astmt | procstmt | cmpdstmt | writestmt ::= writeln ( exp ) ::= ID optexplist ::= if exp then stmt else stmt | if exp then stmt ::= while exp do stmt ::= begin stmtlist end ::= lvalue := exp ::= ( explist ) | <empty string> ::= explist , exp | exp ::= exp + exp | exp - exp | - exp | exp * exp | exp div exp | exp != exp | exp == exp | exp > exp | exp < exp | exp and exp | exp or exp | not exp | ( exp ) | ID ( explist ) | lvalue | constant ::= ID | ID [ exp ] ::= integer_constant | char_constant | true | false
lvalue constant
1
Your project should produce a listing, identify any syntax errors, and print a list of identiers (not including reserved words) and operators encountered during the parse. Please see the demo les and their output for the format of this interface. You must detect the following syntax errors: illegal procedure declaration, illegal parameter, illegal variable declaration, illegal statement, and illegal expression. You can use your judgement in other cases, but every program with illegal syntax should be reported as an error. Error recovery is not an important goal of this project, but your parser should to try continue normal processing at some point after reporting errors. However, you dont need to worry about some errors that are tricky to recover from, for example, a missing END statement for some block constructs. Reporting multiple errors for the same situation is acceptable when reasonable. You must enforce the following precedence and associativity for each operator: Operator Relational operators + - or div and not unaryPrecedence lowest Associativity not associative left associative left associative right associative
highest
A scanner is supplied for your convenience. You will note that not all tokens identied by your scanner are used by the parser.
Getting Started
All the material for this project is in available through the class website. You can create a dummy parser by typing make. For this project you should only need to change the le parse.y. The parse.y provided to you is to illustrate some examples of Yacc/Bison action items. You are not given a part of a working parser, so most likely, you will have to change everything to build a legal parser. All questions regarding the project should be posted in our news group uh.nsm.cosc4310, with a copy to the instructor and/or TA as approp...