/*
 *  Copyright (c) 1999-2003, Gene Cooperman; Rights to copy and distribute
 *  for non-commercial purposes only are freely granted, but only as
 *  long as this copyright statement remains.  No warranty is implied.
 */
import java.util.ArrayList;
import java.io.*;

/**
 * Read <a href=
 *     "http://java.sun.com/j2se/1.4.2/docs/api/java/io/StreamTokenizer.html">
 * http://java.sun.com/j2se/1.4.2/docs/api/java/io/StreamTokenizer.html</a>
 * for a description of basic concepts.
 */
class SchemeReader extends StreamTokenizer {
    SchemeReader( InputStream in ) {
	this( new BufferedReader( new InputStreamReader( in ) ) );
    }
    SchemeReader( Reader r ) { super(r); init(); }
    void init() {
	// Lower than '!' is whitespace by default.
	whitespaceChars(' ', ' ');
	whitespaceChars('\t', '\t');
	whitespaceChars('\n', '\n');
	whitespaceChars('\r', '\r');
	wordChars( '!', '~' );
	commentChar(';');
	slashSlashComments( false ); // should be default anyway
	slashStarComments( false ); // should be default anyway
	quoteChar('"');
	lowerCaseMode( true );
	ordinaryChar('('); // token by itself, not word, et al.
	ordinaryChar(')'); // token by itself, not word, et al.
	ordinaryChar('\''); // token by itself, not word, et al.
	ordinaryChar('\\'); // token by itself, not word, et al.
	parseNumbers(); // If it works as a number, do it.
	// Problem for 3 char symbol:  a\ b
	// 1abc is a word in Scheme;  Does this do the same thing?
    }
    public int nextToken() throws IOException {
	int tokenType = super.nextToken();
	// if ( ttype == '\' ) Get next character.
	return tokenType;
	// TT_NUMBER, nval
	// TT_WORD, sval
	// string, sval set, and ttype = '"'
	// single character token ('), ttype
	// TT_EOF
	// escape character (\) ???
    }
    /**
     * @param void
     * @return SchemeObject or else #f if it saw only ")"
     */
    public SchemeObject nextExpression( ) throws IOException {
	SchemeObject result = nextExpression2();
	if (result == null) {
	    System.err.println("Scheme:  Unmatched parenthesis returned");
	    return Symbol.schemeFalse;
	}
	else
	    return result;
    }
    SchemeObject make_list_from_sequence(ArrayList al) {
	SchemeObject expr = Symbol.schemeNil;
	for (int i = al.size() - 1; i >= 0; i--)
	    expr = new Cons( (SchemeObject)al.get(i), expr );
	return expr;
    }
    /**
     * @param void
     * @return SchemeObject or else null if it saw only ")"
     */
    public SchemeObject nextExpression2() throws IOException {
	while( true ) {
	    switch ( this.nextToken() ) {
	    case ')': /* end of list */
	        return null;
	    case '(': /* Read list */
		ArrayList al = new ArrayList();
		SchemeObject expr = null;
		while( (expr = nextExpression2()) != null )
		    al.add(expr);
		return make_list_from_sequence(al);
	    case '\'': /* 'x => (quote x) */
	        return new Cons( SchemeInterpreter.obArray.get("quote"),
			      new Cons( nextExpression(), Symbol.schemeNil ) );
	    case '"': /* "string" */
		// Should have been SchemeString, if it were implemented
		return new Symbol(sval);
	    case TT_WORD:
		// StreamTokenizer defines sval when nextToken() is called.
		return SchemeInterpreter.obArray.getOrAdd( this.sval );
        case '-':
                //StreamTokenizer bug: - yields '-', not TT_WORD (cf. wordChars)
                return SchemeInterpreter.obArray.getOrAdd( "-" );
	    case TT_NUMBER:
		// Should distinguish betwene Fixnum and SchemeFloat,
		//   if it were implemented.
		return new Fixnum( (int)this.nval );
	    case TT_EOL:
		System.exit(1);
	    }
	}
    }
}