CPSC 460/560
Project Part 2: mingrammar, minyacc.y, minlex.l
The Parser

Syntactical Analysis

This is the second part of the compiler development project that we are doing this semester. Recall, you are building a compiler for the minl programming language. Minl is a minimal programming language containing just enough high level features to write useful code. (Remember that this is an approach to building a compiler for a full version of a language.) The first part of the project had you construct the lexical analyzer using the Lex tool. This part of the assignment requires you to analyze the syntactical correctness of the input using the Yacc (yet another compiler compiler) tool. Specifically, you are to write a Yacc specification for the grammar of the minl language. The details of the language features are given as a set of separate syntax diagrams. A syntax diagram is a directed graph with one entry and one exit. Each path through the graph defines an allowable sequence of symbols. Rounded boxes denote the tokens seen in the input (as returned by the scanner). Rectangular boxes denote the names of other syntax diagrams. Some additional details of the language include:

The operators $+, -$ and $*$ are left associative.
Multiplication (the $*$ operator) has precedence over the $+$ and $-$ operators.

Approach

First, you should develop a context-free grammar for the minl language specified by the syntax diagrams. Then, you should specify your grammar in Yacc. When you execute yacc to build a parser for the grammar you specified, you must be sure that it reports no conflicts; otherwise, you will need to modify the grammar. To help you convert this later to yacc, use the following rules: instead of writing:

expr -> expr + term | term
term -> DIGIT

use yacc format:

expr : expr + term 
      | term
      ;
term : DIGIT
       ;

Hand this in (typed, so you will have it for your yacc source) by Wednesday, Monday March 26. This will count as a homework.

yacc

use of yacc is similar to lex. Your book gives a simple user's guide on pages 287-297 (the subsection is entitled ``The Parser Generator Yacc''). I have typed figure 4.59 on a web page so you can practice. You can compile this program, then type in expressions such as: 4+5, and the program will tell you 9 (remember, no spaces are allowed and you may only use single digits).

To Hand In

First the grammar. Type this into a text file named grammar. Next, turn in the yacc program: all the code needed to build a fully-functional parser. Note that this necessarily includes a scanner (which you've already built, but it may need to be modified a little). This should be contained in two files: minyacc.y and minlex.l The parser for this assignment should output: 1) An accepted or not accepted answer depending upon whether or not the input matches the grammar specifications or not; and, 2) The series of grammar rules applied for accepting the input. Diagram 1 and Diagram 2

Example Input

program myprog;
int v;
begin
v = 3;
end

Example Output

VARDECLS -> v 
DECL -> int VARDECLS
DECLIST -> DECL ;
TERM -> 3
EXPR -> TERM
ASGNSTMT -> v = EXPR
STMT -> ASGNSTMT
STMTLIST -> STMT ;
start -> program myprog ; DECLIST begin STMTLIST end


Program myprog accepted

To hand in

You will need two files, your lexical analyzer and your parser.

CPSC 460/560 Project Part 2: mingrammar, minyacc.y, minlex.l The Parser