Raise exceptions in built-in functions

[julianhyde]

The specifications of built-in functions String.sub, String.extract, String.concat, String.concatWith, List.hd, List.tl, List.last, List.nth, List.take, List.tabulate require them to throw exceptions Empty, Subscript, Size. (See, for example, the String structure in Standard ML basis library.)

Change the implementations of those functions to raise exceptions. The exception is printed on the console, for example

String.sub("abc", ~1);
uncaught exception Subscript [subscript out of bounds]

This change does not allow the user to define, raise or handle exceptions (keywords exception, raise, handle).

[julianhyde]

Fixed in 0cedd58 (release 0.3).