Homework 4
Interpreter of Straight-line Program  

• Overview
• Assignment
• Files
• Getting Started
• Turn In
• Resources

Overview

Homework 1 implemented an interpreter for a simple language called StraightLine (not iterators, functions, data structures, just assignment, print and compound statements). A parser constructs an Abstract Syntax Tree (AST) from a program's text, from Homework 1 we know that the program can be interpreted while traversing the AST. In Homework 1 StraightLine programs were entered in the intermediate AST representation as below:

Text	AST
37	new NumExp(37)	NumExp(37)
a = 37	new AssignStm("a", new NumExp(37))	AssignStm       /  \    "a"  NumExp(37)
a := 5 + 3 ; print ( a ) ;	new CompoundStm(        new AssignStm( "a",            new OpExp(               new NumExp(5),               OpExp.Plus,               new NumExp(3)            )         ),         new PrintStm(              new LastExpList(                    new IdExp("b")              )          ) );	CompoundStm                    /                 \             AssignStm             PrintStm                /       \                 /          \           "a"    OpExp         LastExpList  IdExp("b")                  /      |       \ NumExp(5) OpExp.Plus NumExp(3)

Interpreting the parser produced AST is essentially the function of scripting languages such as Perl, Python, etc.

Chapter 4 notes discussed concrete and abstract grammars, we will use the abstract grammar transformation of SableCC3. 

Assignment

1. complete the given skeleton of the Interpreter
2. interpret the 2 given StraightLine programs. The skeleton will interpret only the test1 StraightLine program given below.   

Files

Download the following files:

1. Interpreter.java - Interpreter skeleton.
2. Main.java - Calls lexer, parser and interpreter.
3. StraightLine.js - StraightLine grammar.
4. Test 1, 2 - test programs.

Getting Started

• SableCC - Note that SableCC3 must be used for concrete to abstract transformations.
  1. Download StraightLine.js.
  2. To generate the SableCC lexical analyzer:

     Home:    java -jar \sablecc-3-beta.3.altgen.20041114\lib\sablecc.jar StraightLine.js

     IUS:      java -jar v:\common\user\C431\sablecc.jar StraightLine.js
      

  3. Download Main.java and Interpreter.java to the sub-directory named StraightLine.
  4. To delete an older version of the analyzer and compile the Java program in StraightLine enter:

     del StraightLine\*.class

     javac -classpath . StraightLine\*.java
      

  5. To parse and interpret straightline program test1:

     java -cp . StraightLine.Main < test1

Turn In

1. Cover sheet with your name, C431, date, and Homework 4.
2. Print out of Interpreter.
3. Email Interpreter.java to: with subject: HW4 Solution
4. Print out of test results for test1 and test2.

Resources

Chapter 4 - CONCRETE versus ABSTRACT SYNTAX

SableCC3 - Concrete to Abstract tutorial