transcendental-lisp/src/function/UserDefinedFunction.java

package function;

import java.util.ArrayList;

import function.builtin.EVAL;
import function.builtin.special.SETF;
import sexpression.*;
import table.SymbolTable;

public class UserDefinedFunction extends LispFunction {

    private String name;
    private Cons body;
    private Cons lambdaExpression;
    private SymbolTable scope;
    private ArrayList<String> formalParameters;
    private ArgumentValidator argumentValidator;

    public UserDefinedFunction(String name, Cons lambdaList, Cons body) {
        this.name = name;
        this.body = body;
        this.lambdaExpression = new Cons(new Symbol(name), new Cons(lambdaList, body));
        this.scope = SETF.getSymbolTable();

        for (this.formalParameters = new ArrayList<>(); lambdaList.consp(); lambdaList = (Cons) lambdaList.getCdr())
            this.formalParameters.add(lambdaList.getCar().toString());

        this.argumentValidator = new ArgumentValidator(this.name);
        this.argumentValidator.setExactNumberOfArguments(this.formalParameters.size());
    }

    public SExpression call(Cons argumentList) {
        argumentValidator.validate(argumentList);

        // bind the values of the arguments to the formal parameter names
        bindParameterValues(argumentList);

        // store the environment of the S-expression that called this function
        // (the current environment)
        SymbolTable callingScope = SETF.getSymbolTable();

        // replace the current environment with the environment of this
        // function
        SETF.setSymbolTable(scope);

        Cons currentSExpression = body;
        SExpression lastValue = null;

        // evaluate all the S-expressions making up this function's body
        while (currentSExpression.consp()) {
            lastValue = EVAL.eval(currentSExpression.getCar());
            currentSExpression = (Cons) currentSExpression.getCdr();
        }

        // replace the environment of the S-expression that called this
        // function
        SETF.setSymbolTable(callingScope);

        // remove the bindings of the arguments to the formal parameter names
        // in the environment of this function
        releaseParameterValues();

        return lastValue;
    }

    private void bindParameterValues(Cons argumentList) {
        scope = new SymbolTable(scope);

        for (String parameter : formalParameters) {
            SExpression currentArg = argumentList.getCar();
            scope.put(parameter, currentArg);
            argumentList = (Cons) argumentList.getCdr();
        }
    }

    private void releaseParameterValues() {
        scope = new SymbolTable(scope.getParent());
    }

    public Cons getLambdaExpression() {
        return lambdaExpression;
    }

}