46 lines
1.3 KiB
Java
46 lines
1.3 KiB
Java
|
/*
|
||
|
|
* Name: Mike Cifelli
|
||
|
|
* Course: CIS 443 - Programming Languages
|
||
|
|
* Assignment: Lisp Interpreter 1
|
||
|
|
*/
|
||
|
|
|
||
|
|
package eval;
|
||
|
|
|
||
|
|
import parser.*;
|
||
|
|
|
||
|
|
/**
|
||
|
|
* <code>EQ</code> represents the EQ function in Lisp.
|
||
|
|
*/
|
||
|
|
public class EQ extends LispFunction {
|
||
|
|
|
||
|
|
// The number of arguments that EQ takes.
|
||
|
|
private static final int NUM_ARGS = 2;
|
||
|
|
|
||
|
|
public SExpression call(Cons argList) {
|
||
|
|
// retrieve the number of arguments passed to EQ
|
||
|
|
int argListLength = LENGTH.getLength(argList);
|
||
|
|
|
||
|
|
// make sure we have received the proper number of arguments
|
||
|
|
if (argListLength != NUM_ARGS) {
|
||
|
|
Cons originalSExpr = new Cons(new Symbol("EQ"), argList);
|
||
|
|
String errMsg = "too " +
|
||
|
|
((argListLength > NUM_ARGS) ? "many" : "few") +
|
||
|
|
" arguments given to EQ: " + originalSExpr;
|
||
|
|
|
||
|
|
throw new RuntimeException(errMsg);
|
||
|
|
}
|
||
|
|
|
||
|
|
SExpression argOne = argList.getCar(); // first argument
|
||
|
|
Cons cdr = (Cons) argList.getCdr();
|
||
|
|
SExpression argTwo = cdr.getCar(); // second argumnet
|
||
|
|
|
||
|
|
if (argOne.atomp() && argTwo.atomp()) {
|
||
|
|
return ((argOne.toString().equals(argTwo.toString()))
|
||
|
|
? Symbol.T : Nil.getUniqueInstance());
|
||
|
|
}
|
||
|
|
|
||
|
|
return ((argOne == argTwo) ? Symbol.T : Nil.getUniqueInstance());
|
||
|
|
}
|
||
|
|
|
||
|
|
}
|