From lliao@ren.eecis.udel.edu Mon Oct 28 22:56:52 2002
Date: Mon, 28 Oct 2002 22:55:23 -0500 (EST)
From: Li Liao <lliao@ren.eecis.udel.edu>
Subject: Re: hw3 sample solution





On Mon, 28 Oct 2002, Greg Forte wrote:

> On Mon, 28 Oct 2002, Li Liao wrote:
>
> > Attached please find the sample solution to homework 3.
> > It may be helpful for you to prepare for tomorrow's midterm.
> > Good luck. See you tomorrow.
>
> I think there's a problem with the solution to problem 2.  As I
> understand it (and as shown in Harper's "Programming in Standard ML"),
> the expression "_exp1_ andalso _exp2_" is shorthand for

as one way of implementing short-circuit evaluation

> "if _exp1_ then _exp2_ else false", which would mean that the
> two functions presented in the solution are in fact identical ...

Syntactically, without short-circuit effect, the sample solution
should be fine. But you certainly made a very good point here.
Your solution below is better, for which you should earn extra credits.

Thanks for your comments.

Li


>
> If my solution was correct, the non-tail-recursive version should
> have the arguments reversed, i.e.
>
> isord (t2::ts) andalso (t1 <= t2)
>
> Is that correct?
>
> -g
>
>
>