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5 Closureクラス

Closureクラスは，Procedureクラスのサブクラスで， Evalの中で，lambda式がきたところでインスタンスが作られています．


package jscheme;

/** A closure is a user-defined procedure.
 *  It is "closed" over the
 * environment in which it was created.
 *  To apply the procedure, bind
 * the parameters to the passed in variables,
 * and evaluate the body.
 * @author Peter Norvig,
 * peter@norvig.com http://www.norvig.com 
 * Copyright 1998 Peter Norvig,
 * see http://www.norvig.com/license.html **/

public class Closure extends Procedure {

    Object parms;
    Object body;
    Environment env;
    
    /** Make a closure from a parameter list,
     * body, and environment. **/
    public Closure (Object parms,
                    Object body,
                    Environment env) {
        this.parms = parms;
        this.env = env;
        this.body =
           (body instanceof Pair &&
              rest(body) == null)
           ? first(body)
           : cons("begin", body);
    }

    /** Apply a closure to a list
     * of arguments.  **/
    public Object apply(Scheme interpreter,
                        Object args) {
        return interpreter.eval(body,
                    new Environment(parms,
                                    args, env));
    }
}

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