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1b (Smalltalk).

Here are four marks of homework. You only need to get 3 marks for full amrks (so 1 is extra).

You will need my Smalltalk tools.

1b1. Number collector (0.5 marks)

Write a Magic subclass called Num that is equivalent to the following.

 function num(txt)  
     return {n=0, mu=0, m2=0, sd=0, id = id(), 
             lo=10^32, hi=-1*10^32, txt=txt,
             w=1}
 end

 function numInc(t,x,    d) 
   if x == "?" then return x end
   t.n  = t.n + 1
   d    = x - t.mu
   t.mu = t.mu + d/t.n
   t.m2 = t.m2 + d*(x - t.mu)
   if x > t.hi then t.hi = x end
   if x < t.lo then t.lo = x end
   if (t.n>=2) then 
     t.sd = (t.m2/(t.n - 1 + 10^-32))^0.5 end
   return x  
 end

 function numDec(t,x,    d) 
   if (x == "?") then return x end
   if (t.n == 1) then return x end
   t.n  = t.n - 1
   d    = x - t.mu
   t.mu = t.mu - d/t.n
   t.m2 = t.m2 - d*(x- t.mu)
   if (t.n>=2) then
     t.sd = (t.m2/(t.n - 1 + 10^-32))^0.5 end
   return x
 end

When that works, it should do the following:

 FileStream fileIn: 'my.st' "mytricks" !
 FileStream fileIn: 'num.st' "yourcode" !

 | num |
 num := Num new.
 num nextPutAll: #( 2 3 4 4 4 4 5 5 6 7 7
                  8 9 9 9 9 10 11 12 12).
 num sd oo. "==> 3.06"
 num mu oo. "==> 7"
 num n  oo. "==> 20" !

1b2. Iterators (0.5 marks)

Go to /usr/share/gnu-smalltak/kernel and browse the Collection.st class. Reflect on the methods reject: and select: methods.

Write your own reject: method called eject: that does the same thing as reject: but do so calling select.

e.g.

 #(1 2 3) eject: [:x | x > 1.5]

 (1)

IMPORTANT: do not edit anything in that kernel directory.

HINT: the solution is two lines long.

1b3. Iterators (0.5 marks)

Write an iterator b4Now: that pass the i-th and (i+1)-th item to a alist:

e.g.

FileStream fileIn: 'my.st' !

#(10 21 32 43 54) b4Now: [:b4 :now|
     ((now-b4)/b4) asFloat oo] !x!

1.1
0.5238095238095238
0.34375
0.2558139534883721

1b4. Polymorphism (1.5 marks)

My Magic class has a method called visit that walks a block across all instance variables. Write more methods (not in Magic) such that you can write a generic visit that walks across anything in Smalltalk (exception, the C* classes that talk to C structs.

Magic sub: #Employee has: 'name age shoesize'

! Employee methods !
init
  self name: 'freda';
       age:  21;
       shoesize:  0 !

printOn: aStream
  aStream 
     nextPutAll: 'Emp(';
     nextPutAll: ':name ',name s;
     nextPutAll: ' :age ',age s;
     nextPutAll: ' :shoesize ',shoesize s;
     nextPutAll: ')' !
!

! Magic methods !
visit: aBlock
  "To heck with encapulation. Walk over the instance vars."
  | num |
  num := self class instSize + self basicSize.
  1 to: num do: [:i | 
     (self instVarAt: i) visit: aBlock ] !
!

! Object class methodsFor: 'testing' !
goodVisit
    |x y z w|
    x := (Employee new)  name: 'tammy'.
    y := (Employee new)  name: 'tammy'.
    z := (Employee new)  name: 'Huy'; age: 18.
    w := {1. 2. #abc z. {x. x. x. {y.}.}. 4. {{{5.}.}.}.}.
    w visit:[:a| a oo] !
!

Output:

1
2
#abc
'Huy'
18
0
'tammy'
21
0
'tammy'
21
0
'tammy'
21
0
'tammy'
21
0
4
5

Important: make sure #abc is printed as #abc and not:

$a
$b
$c

To test this one, run

FileStream fileIn: 'my.st'.
FileStream fileIn: 'yourcode.st'.
Object goodVisit.

Then you should see something like the above (and don't worry if you see stuff that is a little difference).

1b5. 1 marks.

This is the extra mark one. Its a little tricky since you'll need to hunt around looking for some magic methods.

For each of the following, include a litte test script showing off what can be done.

My file my.st hows an exampe of class methods contain tests in the category 'testing'. Write some test cases for your classes using the same category (and call all those methods goodX, just like I did). Write Smalltalk code to

  • iterate through all classes (hint allSubclasses)
  • iterate through all methods of class methods categories called 'testing'
  • run all class methods in category testing (hint methodDictionary and perform:) count how pass,fails you get
  • run methods such that if any one test method fails, the result gets recorded as "fail" and the test carries on to the next method.
  • Hint: see Gnu Smaltalk manual and on:do:.