Introduction to Simple Language Programs
1
AspectJ Assignment
2
The simple language
•
Tiny program
y=2;
x=2+y*3;
z=x+y*2;
–
A program is a sequence of assignments;
–
Expressions on the right hand side of assignment statements are arithmetic
expressions;
–
Assume variables are always of integer types;
–
Arithmatic operators include +, -, *, and /. There are no other operators.
–
Assume input is always correct.
3
Parsing
•
The parser creates an abstract syntax tree represented in Program class
public class UseParser {public static void main(String[] args) {try {File inputFile = new File("calc.tiny");Calc2Parser parser = new Calc2Parser(new Calc2Scanner(
new FileReader(inputFile)));
Program pm = (Program) parser.parse().value;
System.out.println(pm.toString());
} catch (Exception e) {e.printStackTrace();
}
}
}
4
Parsing result for z=x+y*2
<?xml version="1.0" encoding="UTF-8" ?>
-
<
program
>
-
<
assignment
>
<
lhs
>
z
</
lhs
>
-
<
rhs
>
-
<
expr
>
<
op
>
+
</
op
>
-
<
left
>
-
<
expr
>
<
primitive
>
x
</
primitive
>
</
expr
>
</
left
>
-
<
right
>
-
<
expr
>
<
op
>
*
</
op
>
-
<
left
>
-
<
expr
>
<
primitive
>
y
</
primitive
>
</
expr
>
</
left
>
-
<
right
>
-
<
expr
>
<
primitive
>
2
</
primitive
>
</
expr
>
</
right
>
</
expr
>
</
right
>
</
expr
>
</
rhs
>
</
assignment
>
… …
Program.java
Assignment.java
Expr.java
5
Program class consists of a vector of statements
public class Program {private Vector <Statement> statements;
public static Hashtable<String, Expr> varTable=new Hashtable<String, Expr>();
public Program(Statement s) {statements = new Vector <Statement>();
statements.add(s);
}
public Program(Statement s, Program p) {statements = p.getStatements();
statements.add(s);
}
public String toString(){ …}
}
6
Assignment class
public class Assignment extends Statement{private String lhs; private Expr rhs;
public Assignment(String l, Expr r){lhs=l;
rhs=r;
Program.varTable.put(l, r);
}
public String getLHS(){ return lhs;}public Expr getRHS() {return rhs; }}
7
Your output
Assignment 0 is: y=2
2==> ?
2==>2
Assignment 1 is: x=(2+(y*3))
(2+(y*3))==> ?
2==> ?
2==>2
(y*3)==> ?
y==> ?
2==> ?
2==>2
2==>2
3==> ?
3==>3
(2*3)==>6
(2+(2*3))==>8
Assignment 2 is: z=(x+(y*2))
(x+(y*2))==> ?
x==> ?
(2+(2*3))==> ?
2==> ?
2==>2
(2*3)==> ?
2==> ?
2==>2
3==> ?
3==>3
(2*3)==>6
(2+(2*3))==>8
8==>8
(y*2)==> ?
y==> ?
2==> ?
2==>2
2==>2
2==> ?
2==>2
(2*2)==>4
(8+(2*2))==>12
Number of Expressions:11
8
Print out the program
•
Print out the parsed program
y = 2;
x = (2+(y*3));
z = (x+(y*2));
•
Suppress printout in the parser by
skipping calls to
System.out.println(..) in UseParser
void around() : call(* *..print*(..))
&& !within(A2) { }Note that
call(* System.out.println(..))
Won’t work
public class UseParser {public static void main(String[] args) throws Exception{File inputFile = new File("calc.tiny");Calc2Parser parser = new Calc2Parser
(new Calc2Scanner(
new FileReader(inputFile)));
Program pm = (Program) parser.parse().value;
System.out.println(pm.toString());
}
}
9
Print out the parsed program
•
Define your own print method in classes such as
Expr, Assignment.
•
Note that the method will be added inside the
Expr class.
public String
Expr.print(){String result="";
if (this.isPrimitive() && this.getValue() != null) {return this.getValue().toString();
} else if (this.isPrimitive() && this.getID() != null) {result=this.getID();
} else {String op = this.getOp();
Expr left = this.getLeft();
Expr right = this.getRight();
result= "("+left.print()+op+right.print()+")";}
return result;
}
public class Expr {private Integer value;
private boolean primitive = false;
private String id;
private Expr left;
private Expr right;
private String op;
public Expr() {super();
}
public Expr(Expr l, Expr r, String o) {left = l;
right = r;
op = o;
}
public Expr(Integer i) {value = i;
primitive = true;
}
… …
}
10
Print out the total number of expressions in this program
•
count calls to constructors
static int Expr.exprCount=0;
after(Expr e): execution( Expr.new(..)) && this(e) {e.exprCount++;
}
11
Evaluate the program
y===>2
x===>8
z===>12
•
add evaluation method into Expr class
public Integer Expr.evaluate() {Integer val;
if (this.isPrimitive() && this.getValue() != null) {return this.getValue();
} else if (this.isPrimitive() && this.getID() != null) {val = Program.varTable.get(this.getID()).evaluate();
} else {String op = this.getOp();
Expr left = this.getLeft();
Expr right = this.getRight();
if (op.equals("+")) {val = left.evaluate() + right.evaluate();
} else if (op.equals("*")) {val = left.evaluate() * right.evaluate();
…
public class Expr {private Integer value;
private boolean primitive = false;
private String id;
private Expr left;
private Expr right;
private String op;
public Expr() { super(); }public Expr(Expr l, Expr r, String o) {left = l;
right = r;
op = o;
}
public Expr(Integer i) {value = i;
primitive = true;
} …
}
12
Print indented trace of the evaluation process
–
check JoinPointTraceAspect in account example
–
Count the nested level
before(): call(* *.evaluate()){indentLevel++;
Expr exp = (Expr) thisJoinPoint.getTarget();
for (int i = 0, sp = indentLevel * 3; i < sp; i++)
System.out.print(" ");System.out.println(exp.print() + "==> ?");
}
In this content, you will explore the basics of writing programs in a simple language, focusing on assignments, arithmetic expressions, parsing, and creating abstract syntax trees. The examples provided demonstrate how to work with variables, operators, and sequences of assignments. Learn about the structure of programs, parsing results, and the implementation of classes like Program and Assignment. Enhance your understanding of programming concepts through practical examples and explanations.
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Presentation Transcript
The simple language Tiny program y=2; x=2+y*3; z=x+y*2; A program is a sequence of assignments; Expressions on the right hand side of assignment statements are arithmetic expressions; Assume variables are always of integer types; Arithmatic operators include +, -, *, and /. There are no other operators. Assume input is always correct. 2
Parsing The parser creates an abstract syntax tree represented in Program class public class UseParser { public static void main(String[] args) { try { File inputFile = new File("calc.tiny"); Calc2Parser parser = new Calc2Parser(new Calc2Scanner( new FileReader(inputFile))); Program pm = (Program) parser.parse().value; System.out.println(pm.toString()); } catch (Exception e) { e.printStackTrace(); } } } 3
Parsing result for z=x+y*2 <?xml version="1.0" encoding="UTF-8" ?> - <program> - <assignment> <lhs>z</lhs> - <rhs> - <expr> <op>+</op> - <left> - <expr> <primitive>x</primitive> </expr> </left> - <right> - <expr> <op>*</op> - <left> - <expr> <primitive>y</primitive> </expr> </left> - <right> - <expr> <primitive>2</primitive> </expr> </right> </expr> </right> </expr> </rhs> </assignment> Program.java Assignment.java Expr.java 4
Program class consists of a vector of statements public class Program { private Vector <Statement> statements; public static Hashtable<String, Expr> varTable=new Hashtable<String, Expr>(); public Program(Statement s) { statements = new Vector <Statement>(); statements.add(s); } public Program(Statement s, Program p) { statements = p.getStatements(); statements.add(s); } public String toString(){ } } 5
Assignment class public class Assignment extends Statement{ private String lhs; private Expr rhs; public Assignment(String l, Expr r){ lhs=l; rhs=r; Program.varTable.put(l, r); } public String getLHS(){ return lhs;} public Expr getRHS() {return rhs; } } 6
Assignment 2 is: z=(x+(y*2)) (x+(y*2))==> ? x==> ? (2+(2*3))==> ? 2==> ? 2==>2 (2*3)==> ? 2==> ? 2==>2 3==> ? 3==>3 (2*3)==>6 (2+(2*3))==>8 8==>8 (y*2)==> ? y==> ? 2==> ? 2==>2 2==>2 2==> ? 2==>2 (2*2)==>4 (8+(2*2))==>12 Your output Assignment 0 is: y=2 2==> ? 2==>2 Assignment 1 is: x=(2+(y*3)) (2+(y*3))==> ? 2==> ? 2==>2 (y*3)==> ? y==> ? 2==> ? 2==>2 2==>2 3==> ? 3==>3 (2*3)==>6 (2+(2*3))==>8 Number of Expressions:11 7
Print out the program Print out the parsed program y = 2; x = (2+(y*3)); z = (x+(y*2)); public class UseParser { public static void main(String[] args) throws Exception{ File inputFile = new File("calc.tiny"); Calc2Parser parser = new Calc2Parser (new Calc2Scanner( new FileReader(inputFile))); Suppress printout in the parser by skipping calls to System.out.println(..) in UseParser Program pm = (Program) parser.parse().value; System.out.println(pm.toString()); } } void around() : call(* *..print*(..)) && !within(A2) { } Note that call(* System.out.println(..)) Won t work 8
Print out the parsed program public class Expr { private Integer value; private boolean primitive = false; private String id; private Expr left; private Expr right; private String op; public Expr() { super(); } public Expr(Expr l, Expr r, String o) { left = l; right = r; op = o; } Define your own print method in classes such as Expr, Assignment. Note that the method will be added inside the Expr class. public String Expr.print(){ String result=""; if (this.isPrimitive() && this.getValue() != null) { return this.getValue().toString(); } else if (this.isPrimitive() && this.getID() != null) { result=this.getID(); } else { String op = this.getOp(); Expr left = this.getLeft(); Expr right = this.getRight(); result= "("+left.print()+op+right.print()+")"; } return result; } public Expr(Integer i) { value = i; primitive = true; } } 9
Print out the total number of expressions in this program count calls to constructors static int Expr.exprCount=0; after(Expr e): execution( Expr.new(..)) && this(e) { e.exprCount++; } 10
Evaluate the program y===>2 x===>8 z===>12 public Integer Expr.evaluate() { Integer val; if (this.isPrimitive() && this.getValue() != null) { return this.getValue(); } else if (this.isPrimitive() && this.getID() != null) { val = Program.varTable.get(this.getID()).evaluate(); } else { String op = this.getOp(); Expr left = this.getLeft(); Expr right = this.getRight(); if (op.equals("+")) { val = left.evaluate() + right.evaluate(); } else if (op.equals("*")) { val = left.evaluate() * right.evaluate(); add evaluation method into Expr class public class Expr { private Integer value; private boolean primitive = false; private String id; private Expr left; private Expr right; private String op; public Expr() { super(); } public Expr(Expr l, Expr r, String o) { left = l; right = r; op = o; } } public Expr(Integer i) { value = i; primitive = true; } 11
Print indented trace of the evaluation process check JoinPointTraceAspect in account example Count the nested level before(): call(* *.evaluate()){ indentLevel++; Expr exp = (Expr) thisJoinPoint.getTarget(); for (int i = 0, sp = indentLevel * 3; i < sp; i++) System.out.print(" "); System.out.println(exp.print() + "==> ?"); } 12
