/**
	 * Returns <code>true</code> if the given expression represents constant value.
	 * This value can be a boolean or integer.
	 * @param e the expression to test
	 * @return <code>true</code> if the given expression represents constant value
	 */
	private boolean isConstant(Expression e) {
		if(e instanceof IntegerExpression)
			return true;
		if(e instanceof VnameExpression) {
			VnameExpression vname = (VnameExpression)e;
			if(vname.V instanceof SimpleVname)
				if(((SimpleVname)vname.V).I.spelling.equals(StdEnvironment.trueDecl.I.spelling) 
						|| ((SimpleVname)vname.V).I.spelling.equals(StdEnvironment.falseDecl.I.spelling))
					return true;
		}
		return false;
	}
	
	/**
	 * Returns the boolean value of the given expression that represents a boolean value.
	 * @param e a boolean value
	 * @return the boolean value of the given expression that represents a boolean value
	 */
	private boolean parseBoolean(Expression e) {
		if(e instanceof VnameExpression) {
			VnameExpression vname = (VnameExpression)e;
			if(vname.V instanceof SimpleVname)
				if(((SimpleVname)vname.V).I.spelling.equals(StdEnvironment.trueDecl.I.spelling))
					return true;
				if(((SimpleVname)vname.V).I.spelling.equals(StdEnvironment.falseDecl.I.spelling))
					return false;
		}
		throw new RuntimeException();
	}
	
	/**
	 * Returns an expression representing the given boolean value.
	 * @param val the boolean value that will be represented by the returned expression
	 * @return an expression representing the given boolean value
	 */
	private Expression createBoolean(boolean val) {
		Identifier iAST = new Identifier(val ? "true" : "false", new SourcePosition());
		iAST.decl = val ? StdEnvironment.trueDecl : StdEnvironment.falseDecl;
		SimpleVname vAST = new SimpleVname(iAST, new SourcePosition());
		vAST.type = StdEnvironment.booleanType;
		VnameExpression boolExpression = new VnameExpression(vAST, new SourcePosition());
		return boolExpression;
	}