1. HW3

Homework: 12. Neither Algol 60 nore Algol 68 employs short-circuit evaluation for Boolean expressions. In both languages, however, an if...then...else construct can be used as an expression. Show how to use if...then...else to achieve the effect of short-circuit evaluations.

I believe the right answer should be (just as the one we discussed at class; talk to me if you still do not understand): 
(1) A and then B
    if A then B else false 
(2) A or else B
    if A then true else B

2. There will be a midterm exam.

3. Lab1 will be in Scheme which has not been assigned yet. Will use MzScheme to grade your lab. 

4. DrScheme is a programming env. for Scheme; you may find it very helpful. You can download it from here.

5. The language manual for MzScheme. http://download.plt-scheme.org/doc/372/pdf/mzscheme.pdf

6. Run your own program with MzScheme

Step 1: Save your code as *.scm file. You can do this with any text editor or the programming env. DrScheme.
Step 2: Copy your file *.scm to the directory where you would like to run MzScheme
Step 3: On the prompt, after you type mzscheme, type (load "*.scm")

Play with the fac example:
test 1: type fac on your prompt, you should see the following line
reference to undefined identifier: fac

Now, Save the folllowing fac function as fac.scm and put/upload it to your working directory.
(define fac
        (lambda (x) (if (= x 0) 1 (* x (fac (- x 1))))))

test 2: type (load "fac.scm"), then type fac, you should see
#<procedure:fac>
and (fac 4) should give you 24

7. Let and its variants (next recitation)