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PlantUML is a component that allows to quickly write : * sequence diagram, * use case diagram, * class diagram, * activity diagram, * component diagram, * state diagram * object diagram

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package net.sourceforge.plantuml.jasic;


import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.Reader;
import java.nio.charset.Charset;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

/**
 * This defines a single class that contains an entire interpreter for a
 * language very similar to the original BASIC. Everything is here (albeit in
 * very simplified form): tokenizing, parsing, and interpretation. The file is
 * organized in phases, with each appearing roughly in the order that they
 * occur when a program is run. You should be able to read this top-down to walk
 * through the entire process of loading and running a program.
 * 
 * Jasic language syntax
 * ---------------------
 * 
 * Comments start with ' and proceed to the end of the line:
 * 
 *     print "hi there" ' this is a comment
 * 
 * Numbers and strings are supported. Strings should be in "double quotes", and
 * only positive integers can be parsed (though numbers are double internally).
 * 
 * Variables are identified by name which must start with a letter and can
 * contain letters or numbers. Case is significant for names and keywords.
 * 
 * Each statement is on its own line. Optionally, a line may have a label before
 * the statement. A label is a name that ends with a colon:
 * 
 *     foo:
 * 
 * 
 * The following statements are supported:
 * 
 *  = 
 *     Evaluates the expression and assigns the result to the given named 
 *     variable. All variables are globally scoped.
 *     
 *     pi = (314159 / 10000)
 *     
 * print 
 *     Evaluates the expression and prints the result.
 * 
 *     print "hello, " + "world"
 * 
 * input 
 *     Reads in a line of input from the user and stores it in the variable with
 *     the given name.
 *     
 *     input guess
 *     
 * goto 
 *     Jumps to the statement after the label with the given name.
 * 
 *     goto loop
 * 
 * if  then 
 *     Evaluates the expression. If it evaluates to a non-zero number, then
 *     jumps to the statement after the given label.
 * 
 *     if a < b then dosomething
 * 
 * 
 * The following expressions are supported:
 * 
 *  = 
 *     Evaluates to 1 if the two expressions are equal, 0 otherwise.
 * 
 *  + 
 *     If the left-hand expression is a number, then adds the two expressions,
 *     otherwise concatenates the two strings.
 * 
 *  - 
 *  * 
 *  / 
 *  < 
 *  > 
 *     You can figure it out.
 * 
 * 
 *     A name in an expression simply returns the value of the variable with
 *     that name. If the variable was never set, it defaults to 0.
 * 
 * All binary operators have the same precedence. Sorry, I had to cut corners
 * somewhere.
 * 
 * To keep things simple, I've omitted some stuff or hacked things a bit. When
 * possible, I'll leave a "HACK" note there explaining what and why. If you
 * make your own interpreter, you'll want to address those.
 * 
 * @author Bob Nystrom
 */
public class Jasic {

    /**
     * Runs the interpreter as a command-line app. Takes one argument: a path
     * to a script file to load and run. The script should contain one
     * statement per line.
     * 
     * @param args Command-line arguments.
     */
    public static void main(String[] args) {
        // Just show the usage and quit if a script wasn't provided.
        if (args.length != 1) {
            System.out.println("Usage: jasic